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Chemical Reactions Notes Jan 10

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January 10, 2019

Chemical Reactions

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Table of Contents: Chemical Reactions

• Balancing Equations

Click on the topic to go to that section

• Types of Chemical Reactions

• OxidationReduction Reactions

• Chemical Equations

• Types of OxidationReduction Reactions• AcidBase Reactions

• Precipitation Reactions

• Identifying Reaction Types: Summary

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Chemical Equations

Chemical Reactions

A chemical reaction is a process in which substance(s) are transformed into new substances .Chemical reactions include:

* breaking and forming chemical bonds

* changing positions of electrons

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Chemical EquationsChemical equations are representations of

chemical reactions using formulas,words, or models.

+ +⇒

CH4(g) + 2O2(g) > CO2(g) + 2H2O(g)

>

Reactant: The starting substance(s)

shows the direction of the reaction and means "forms" or "yields"

Product: The newly formed substance(s) ; the result of the chemical reaction.

To write a word equation1. write the names of the reactants to the left of the arrow

separated by plus signs.

2. Write the names of the products to the right of the arrow, also separated by plus signs.

Reactant + Reactant Product + Product

Chemical Equations

Symbols used in chemical equations Skeleton equationsA skeleton equation is a chemical equation that isn't balanced. (It does not indicate the relative amounts of the reactants and products.)

Here is the equation for rusting:Metallic Iron reacts with oxygen to produce iron (III) oxide (rust).

Iron( s) + Oxygen

( g) ⇒ iron (III) oxide

( s) (word equation)

Fe + O2 à Fe2O3 ( skeleton chemical equation)


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Facts to Remember when Writing Chemical Equations

1. Ionic compounds must be written as neutral formulas.

2. Diatomic elements exist as two atom molecules when in the pure state: H2 N2 O2 F2 Cl2 Br2 I2

1 In the reaction CH4 (g) + O2 (g) à H2O (g) + CO2 (g) the products are:

A oxygen and water B carbon dioxide and water C oxygen and methane D methane and carbon dioxide E I don't know the answer to this.

answ

er2 In the reaction CH4 (g) + O2 (g) à H2O (g) + CO2 (g)

the products are:

A solidsB liquidsC gasesD dissolved in water (aqueous)

E cannot be determined

F I don't know how to answer this.

answ

er

Word equations to Chemical equations

Solid potasium chlorate decomposes in air to produce solid potassium chloride and oxygen gas.

The word equation is:

potasium chlorate (s) > potassium chloride (s) + oxygen (g)

The unbalanced "skeleton" equation is:

KClO3(s) KCl(s) + O2(g)


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Write the word equation, then the skeleton equation Aluminum sulfate reacts with calcium chloride to produce calcium sulfate and aluminum chloride

Al2(SO4)3 + CaCl2 > Ca(SO4) + AlCl3

Word equations to Chemical equations

Aluminum sulfate + calcium chloride > calcium sulfate + aluminum chlorideSlide for Word equation

Slide for Skeleton equation


Balancing Equations

Law of Conservation of Mass (Matter)

“We may lay it down as an incontestable axiom that, in all the operations of art and nature, nothing is created; an equal amount of matter exists both before and after the experiment. Upon this principle, the whole art of performing chemical experiments depends.”

Antoine Lavoisier, 1789

Law of Conservation of MassLaw of Conservation of Mass (Matter): Matter cannot be created or destroyed in a chemical reaction. Atoms can only be rearranged to produce new substances as products.

We MUST balance chemical reactions in order to follow this law. The number and type of atoms must be equal on both sides of a chemical equation.


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Subscripts and Coefficients

Subscripts tell the number of atoms of each element in a molecule. These are part of the formula. Subscripts are never changed or added when balancing an equation.

Coefficients tell the number of representative particles (atoms, molecules, or formula units).

3 How many oxygen atoms are in one formula unit of calcium nitrate? (First, write the formula for calcium nitrate.)

A 2B 3C 5D 6E I don't know how to answer this.

answ

er

4 How many nitrogen atoms are in one formula unit of ammonium sulfate?

answ

er

2

2

1

1 2 2

2 2

H2 + Cl2 à HCl H2 + Cl2 à 2HCl

Balancing chemical equations

unbalanced balanced


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chlorine + sodium bromide à bromine + sodium chloride

Steps to balancing chemical equations

1. First write a skeleton equation(remember diatomic molecules and write neutral ionic formulas)

Cl2 + NaBr à Br2 + NaCl


2. Then, count up the number of each type of element on each side of the reaction


Reactants Products Cl: 2 Cl: 1

Na: 1 Na: 1

Br: 1 Br: 2

Balancing chemical equations3. Next, identify one element that is not balanced.


Reactants ProductsCl: 2 Cl: 1

Na: 1 Na: 1

Br: 1 Br: 2


3. Identify the side that needs more of that particular element and add a coefficient in front of the formula containing the element you are balancing so you have equal atoms of that element on both sides.


Cl2 + NaBr > Br2 + 2NaCl


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Balancing chemical equations4. Continue with these steps until all the elements are balanced.

When all the elements exist in equal amounts on both sides of the equation, you have a balanced chemical equation.

Cl: 2

Na: 1

Br: 1

Cl2 + 2NaBr à Br2 + 2NaClReactants Products

Cl: 2 Cl: 1 2

Na: 1 2 Na: 1 2

Br: 1 2 Br: 2


NOTE: Make sure that when you are calculating amounts of each element, you include that element that may be present in more

than one reactant or product.

CH3OH + O2 à CO2+ H2O


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Special Case: Balancing Combustion of Hydrocarbon Reactions

Hydrocarbons are compounds that contain both C and H. Often times these reactions are difficult to balance; you end up balancing the C and O, but can't balance the Oxygen. Here is how to make this easier.

C3H7 + O2 à CO2+ H2O

1. Balance the C and H.2. Temporarily use a fraction in front of the O2 to balance it.3. Multiply ALL the coefficients by a number (usually a 2 because you will usually have a #1/2 in front of the oxygen) to make all the coefficients a whole number.

Coefficients in a balanced equations must be in the lowest whole number ratio.

In the following example you would have to divideall the coefficients by 2 to be correct:

4 Na + 2 Cl2 > 4 NaCl

Corrected : 2 Na + Cl2 > 2 NaCl

If you are having trouble balancing an equation...

1. check that all your ionic formulas are writtencorrectly (They must be neutral)

2. be sure you have your diatomic elements written correctly (H2 etc)


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5 When the following equation is balanced, the coefficients are:

A 1, 1, 1 B 1, 2, 4

C 4, 1, 2

D 2, 2, 1

E 4, 1, 4

Na + O2 à Na2O

answ

er6 When the following equation is balanced, the

coefficients are

HgO à Hg + O2

A 1, 1, 1

B 1, 2, 4

C 4, 1, 2 D 2, 2, 1

E 4, 1, 4

answ

er

7 When the following equation is balanced, the coefficients are

Al + ZnCl2 à Zn + AlCl3

A. 1,1,1,1

B. 4,7,4,6

C. 2,3,2,3,

D. 1,3,1,2

E. 2,3,3,2


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January 10, 2019


A 1, 1, 1, 1

B 3, 2, 2, 3

C 2, 3, 2, 3

D 1, 3, 1, 2

E 2, 1, 2, 1

NaCl + CaI2 à NaI + CaCl2


NH3 + O2 à NO2 + H2O

A 1, 1, 1, 1 B 3, 2, 2, 3 C 2, 3, 2, 3

E answ

er

D 1,3,1,2 E 4,3,4,3

10 When the following equation is balanced, the coefficients are Al(NO3)3 + Na2S à Al2S3 + NaNO3

answ

er

A. 2, 3, 1, 6

B. 2, 1, 3, 2

C. 1, 1, 1, 1

D. 4, 6, 3, 2

E. 2, 3, 2, 3


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Reaction Types

Precipitation: formation of insoluble product out of aqueous solutions

Oxidation/Reduction: exchange of electrons between atoms/ions

Acid/Base: reaction between acids and bases

Most reactions can be classified as one of the following:


Precipitation Reactions

Precipitation ReactionsThe giant clam's shell is made from the precipitation of CaCO3

Precipitation reactions involve the reaction of water soluble ionic compounds to form a water insoluble product called a precipitate. Because precipitates are NOT soluble, when they form, they make the solution cloudy, and will eventually settle to the bottom.

AgNO3(aq) + NaCl(aq) > AgCl(s) + NaNO3(aq)

AgCl precipitate


The insoluble product is labeled with the subscript (s) for solid.


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What happens when substances dissolve in water?

Ionic substances dissociate when dissolved in water. This means that the water pulls the ions apart, and the ions exist independently, surrounded by water molecules in the solution.

Molecular substances dissolve, but do not dissociate.What this means is that the molecules (say of sugar) separate from other molecules of sugar and become surrounded by water molecules (dissolved).The sugar molecules stay as single sugar molecules.

Use your solubililty table to determine which ionic compounds are water soluble and which are not. It is the insoluble ones that form

precipitates! Some general rules apply:

ALWAYS SOLUBLE

SOMETIMES SOLUBLE

INSOLUBLE

(unless paired with a soluble ion)

Precipitates are insoluble

NH4+, C2H3O2, ClO3, Group 1 A metal ions, NO3

Cl,Br, I except when combined with Ag+, Hg+, and Pb2+

SO42 except when combined with Ag+, Hg+, Pb2+, Ca2+, Sr2+, Ba2+

CO32, PO43, OH, S2, F, O2

Solubility Chart

Note that S on this chart means that the compound is soluble. When you write a chemical equation, label solubel substances with (aq) aqueous.

Insoluble compounds are shown with the letter I. When you write a chemical equation, the insoluble substance is labeled (s) solid.


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11 Which one of the following would be INSOLUBLE in water?

answ

er

A. Na2CO3

B. NH4NO3

C. AgNO3

D. Mg(OH)2E. KCl

12 Which of the following would be MOST SOLUBLE in water?

answ

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A. CaS

B. PbCl2C. PbI2D. Cu(OH)2E. CuSO4

Double Displacement Reactions

Precipitation reactions are often called "double replacement" or "double displacement" reactions because it appears as if the ions switch partners with each other.

NaCl(aq) + AgNO3(aq) > AgCl(s) + NaNO3(aq)

Na+ and Ag+ switch places


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Precipitation ReactionsSome examples of precipitation reactions....

Pb(NO3)2(aq) + 2 KI(aq) à PbI2(s) + 2 KNO3(aq)

AgNO3(aq) + KCl(aq) à AgCl(s) + KNO3(aq)

The formation of an insoluble precipitate is the driving force of these reactions (meaning makes the reaction occur). If no precipitate forms, then the ions stay dissociated in the solution and no reaction has occurred.


A precipitation reaction will NOT occur if both products are water soluble....

2NaNO3(aq) + MgCl2(aq) > 2NaCl(aq) + Mg(NO3)2(aq)

Since both products are soluble, no reaction occurs

To predict the products of a double replacement reaction:1. Identify the cation and anion in each reactant.2. Look up their charges.3. Switch cation and anion pairs and write the formulas for neutral

ionic compounds that would form.4. Check solubility chart and identify states of the products.

K3PO4 (aq) + MgCl2 (aq) > KCl + Mg3(PO4)2


Now, write the phases of the products as subscriptsand balance the equation.

Answer

2K3PO4 (aq) + 3MgCl2 (aq) > 6KCl(aq) + Mg3(PO4)2(s)

Predict the products of this reaction:

CaF2 (aq) + Na2SO4 (aq) > NaF + Ca(SO4)(s)


Next add phases of the products and balance the equation.

CaF2 (aq) + Na2SO4 (aq) > 2NaF (aq) + Ca(SO4)(s)

Answer

Answer


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January 10, 2019

13 Which of the following would be products from the reaction of aqueous Mg(C2H3O2)2 with aqueous Na3PO4?

answ

er

A Mg3(PO4)2(aq) + NaC2H3O2(aq)B Mg3(PO4)2(s) + NaC2H3O2(aq)C Mg3(PO4)2(aq) + NaC2H3O2(s)D Mg3(PO4)2(s) + NaC2H3O2(s)E Mg3(PO4)2(s) + NaC2H3O2(s)

14 One of the products of a reaction between silver nitrate and potassium carbonate will be:

answ

erA. silver potassium (aq)

B. potassium carbonate (aq)

C. nitrate carbonate (aq)

D. potassium nitrate (aq)

E. potassium carbonate (s)

15 Which of the following aqueous solutions could be used to form a precipitate with MgSO4?

answ

er

A. NaCl

B. NH4NO3

C. BaI2D. KC2H3O2

E. LIClO3


OxidationReduction Reactions


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Oxidation/Reduction Reactions

These reactions, often called REDOX reactions, involve a transfer of electrons from one element to another.

4Al(s) + 3O2(g) 2Al2O3

Charge 0 0 +3 2

Each Al loses 3 electrons Each O gains 2 electrons

Oxidation

element loses electronsReduction

element gains electrons

Determining Oxidation StatesIn order to determine if a reaction is an oxidation/reduction reaction and which element got oxidized or reduced, one must be able to track the charges (oxidation states) of elements throughout the reaction.

Zn + 2H+ > Zn2+ + H2

0 +1 +2 0Oxidation States

Since the charges on both the zinc and hydrogen change, this is definitely a redox reaction.

Determining Oxidation States

Substance Oxidation State

H2(g) 0

Ca(s) 0

Na+(aq) +1

F(aq) 1

1. All elements in their standard (neutral) state, have an oxidation state of zero.

2. If the element has a charge listed, this is it's oxidation state. The charges of all the elements in the compound have to add up

to the charge of the compound. Example: ZnO The compound is neutral so...

Charge of Zn + Charge of O = 0

Example: NO3 The compound has a charge of 1 so...

Charge of N + charge of O = 1

Determining Oxidation StatesIf the element is combined with others, the oxidation state will have to be deduced using the periodic table, your knowledge of ionic compounds, and some mathematics. Here are some general guidelines...


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Additional Guidelines:

Alkali metals will always have an oxidation state of +1Alkaline Earth metals will always have an oxidation state of +2Aluminum group will always have an oxidation state of +3The oxidation state of H is +1 when bonded to nonmetals and 1

when bonded to metalsThe oxidation state of oxygen is usually always 2Flourine's oxidation state is always 1Other halogens have an oxidation state of 1 except when they are

bonded to oxygen in polyatomic ions, in which case their oxidationstates are positive.

You must calculate the oxidation state of elements not listed here.

Guideline 1: The charges of all the elements in the compound have to

add up to the charge of the compound.

Example: ZnO ...we know O has a usual ox. state of +2

Zn + O = 0 Zn + 2 = 0 Zn = +2 Zinc has a +2 oxidation state!


Another Example: NO31 So.. N + 3O = 1

we know the oxidations state of Oxygen is 2, so enter that and calculate the oxidation state of N

N + (3 x 2) = 1 N 6 = 1 N = +5

Oxidation States: N = +5 O = 2


Find the oxidation states of Cr and O in Cr2O72

2Cr + 7O = 2 we know the oxid. state of O is 2 2 Cr + (7 x 2) = 2

2Cr = +12 Cr = +6

the oxidation state of Cr is +6!

Oxidation states: Cr = +6 O = 2



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Determine the oxidation states of elements in HS1

H + S = 1 H is with a nonmetal, thus it is acting like a metal

and must have an oxidation state of +1 H = +1, S = 2

Determining Oxidation StatesAnother Example: N2O4

2N + 4O = 0 we know O is 2, solve for N

so.... N = +4, O = 2


Move for answer

Determine the oxidation states of elements in Na2S2O3


.Na =+1, S =+2, and O = 2

16 In which of the following substances would zinc have an oxidation state of 0?

answ

erA. ZnS

B. Zn

C. Zn2+

D. ZnSO4

E. ZnCl2


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17 What is the oxidation state of P in the phosphate ion PO43?

answ

er

A. 0

B. +1

C. +3

D. +5

E. 3

answ

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18 What is the oxidation state of Cl in ClO21?

A. 0

B. 1

C. +1

D. +3

E. +5

Example: KMnO4

charges

K Mn Ox4 KMnO4

+1 ? 2(4)=8 0

1 + 7 8 = 0

So... K = +1, Mn = +7, and O = 2

Determining Oxidation Statesansw

er19 What is the oxidation state of each element in K2TeO4?

A. K = +1 Te = +6 O = 2

B. K = +2 Te = +4 O = 2

C. K = +1 Te = +4 O = 2

D. K = +1 Te = +2 O = 2

E. K = +1 Te = +8 O = 2


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January 10, 2019

20 In which of the following substances would S have an oxidation state of +4?

answ

er

A. Na2SO4

B. Na2SO3

C. Na2S

D. S8

E. SO3

21 In the following equation, the oxidation state of O changes from....

2KClO3 > 2KCl + 3O2

A. 2 to 2

B. 6 to 2

C. 6 to 0

D. 2 to 0

E. 1 to 0

answ

er22 In the following equation, the oxidation state of Cl changes from....

2KClO3 > 2KCl + 3O2

A. 1 to 1

B. 0 to 1

C. +3 to +5

D. +5 to 1

E. +5 to 0

answ

er

Which atom/ion got oxidized/reduced?

To determine which particle in a reaction got oxidized or reduced,

one must know what it means to be oxidized and reduced.Oxidation = Loss of electronsNa > Na+ + e

0 > +1

Notice that an element becomes more positive when it gets oxidized.

Reduction = Gain of electronsMg2+ + 2e > Mg

+2 > 0

Notice that an element becomes less + when it gets reduced.


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Tips for remembering oxidation / reduction:

OIL RIG Oxidation is losing (electrons)Reduction is gaining (electrons)

LEO GER Losing electrons is oxidationGaining electrons is reduction

Which particle got oxidized/reduced?

Which element got oxidized and which got reduced in the following reaction?

2KClO3 > 2KCl + 3O2

Find Ox. States +1,+5, 2 +1,1 0

Oxygen went from 2 > 0 becoming more + so it must have lost electrons

Chlorine went from +5 > 1 becoming less + so it must have gained electrons

reduced oxidized

Which particle got oxidized/reduced?

Which of the following elements got oxidized and reduced in the following reaction?

2F(aq) + Cl2(g) > 2Cl(aq) + F2(g)

1 0 1 0

Flourine went from 1 to 0 becoming more + meaning electrons were lost = oxidation!

Chlorine went from 0 to 1 becoming more meaning electrons were gained = reduction!

Real World Application

Antioxidants like carotenoids found in veggies have many electrons to lose so they help reduced the radicals so the molecules in your body don't get harmed!!! So...eat your veggies!!!

[ ]2

carotenoid >

free radical singlet O >

An oxidant is a chemical species that wants to be reduced so it causes something else to get oxidized. Free radical species like singlet oxygen are oxidants and not good for you as they will get electrons from molecules in your body that need them!

O + 2e > O


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23 Which of the following represents a reduction?

A An elements charge going from 3 > 2B An elements charge going from 2 >3C An elements charge going from 0 > +2D An elements charge going from +1 > +3E None of these

answ

er

24 Which of the following represents an oxidation?

A Al3+(aq) > Al(s)B F2(g) > 2F(aq) C Mn7+ > Mn2+D Fe2+(aq) > Fe3+(aq)E O(aq) > O2(aq)

answ

er25 In which of the following equations does O get oxidized?

A 2H2O2 2H2O + O2

B 2H2O > 2H2 + O2

C CH4 + 2O2 > CO2 + 2H2OD 3Fe + 3O2 > 2Fe2O3

E None of these

answ

er

26 Which of the following is NOT an oxidation/reduction reaction?

A Ca + 2H+ > Ca2+ + H2

B H2 + Cl2 >2HClC 4Al + 3O2 > 2Al2O3

D CaO + CO2 > CaCO3

E Mg3N2 > 3Mg + N2

answ

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January 10, 2019


Types of OxidationReduction Reactions

Types of Oxidation/Reduction Reactions

There are essentially five types of Redox reactions:1. Synthesis or Combination two or more substances combine

2Mg(s) + O2(g) > 2MgO(s)

2. Decomposition a substance breaks into two or more compounds

2LiClO3(s) > 2LiCl(s) + 3O2(g)

3. Combustion a substance reacts with oxygen.

C(s) + O2(g) > CO2(g)

CH4(g) + 2O2(g) > CO2(g) + 2H2O(g)

4. Disproportionation the same material gets both oxidized and reduced

Hg2Cl2 → Hg + HgCl2

5. Single Replacement Reaction: when an single element takes the

place of an element in a compound.

Mg + 2HCl > MgCl2 + 2H2(g)

Types of Oxidation/Reduction Reactions


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Combination/Synthesis Reactions

Examples:

• 2 Mg (s) + O2 (g) 2 MgO (s)• N2 (g) + 3 H2 (g) 2 NH3 (g)• C3H6 (g) + Br2 (l) C3H6Br2 (l)

Identify by pattern of two or more reactants form one product.

Mg O2 MgO

27 Which of the following is a combination reaction?

A H2O > H2 +O2

B Na + Cl2 > NaCl C AgNO3 + BaSO4 > Ag2SO4 + Ba(NO3)2

D C3H8 + O2 > H2O + CO2

E CaCO3 > CaO + CO2

answ

erDecomposition Reactions

Examples:

CaCO3 (s) CaO (s) + CO2 (g)

2 KClO3 (s) 2 KCl (s) + 3 O2 (g)

2 NaN3 (s) 2 Na (s) + 3 N2 (g)

à +

2 H2O à O2 + 2 H2

Identify by the one reactant breaking down to form two or more products.

28 Which of the following is a decomposition reaction?

A H2O > H2 +O2

B Na + Cl2 > NaCl

C AgNO3 + BaSO4 > Ag2SO4 + Ba(NO3)2D C3H8 + O2 > H2O + CO2

E Ca2+(aq) + SO4

2(aq) > CaSO(s)

answ

er


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January 10, 2019

Combustion Reactions

Examples:CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (g)

C3H8 (g) + 5 O2 (g) 3 CO2 (g) + 4 H2O (g)

These are generally rapid reactions that produce a flame.O2 is always one of the reactants.

Hydrocarbons react with oxygen in the air to produce CO2 and H2O.

Combustion ReactionsCombustion reactions are easily identified by oxygen as a reactant. However, the products of combustion of a hydrocarbon may vary depending on how much oxygen is available.

Complete combustion

products are carbon dioxide and water

Incomplete combustion

products are carbon monoxide and water

Combustion Reactions

Note: substances other than hydrocarbons may also undergo combustion:

Mg (s) + O2 (g) > MgO (s)N2 (g) + 2 O2 (g) > 2 NO2 (g)

These may also be classified as combination reactions.

29 Which of the following is a combustion reaction?

A H2O > H2 +O2

B Na + Cl2 > NaCl

C AgNO3 + BaSO4 > Ag2SO4 + Ba(NO3)2

D C3H8 + O2 > H2O + CO2

E Ca2+ + SO42 > CaSO4(s)

answ

er


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January 10, 2019

Single Replacement Reactions

Characteristics:* a single, uncombined element replaces another

element that is part of a compound* reactants are always an element and a compound

Single Replacement Reactions

Examples: Mg + CuSO4 à MgSO4 + Cu

Cl2 + 2KI à 2 KCl + I2

IF the pure element is more active..... Cations formed from the pure element will replace cations in the compound or.... Anions produced by the pure element will replace anions in the compound.

* a more “active” element will replace a “less active” element in a compound

Predicting Single Replacement Reactions Using the Activity Series

An activity series is a list of substances ranked in order of relative reactivity.


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1. Identify the two metals or two halogens in the given reactants.(one will be an element and one will be in a compound)

2. Look up the activity of each. If the single element is more active than it will replace the element in the compound, and a reaction will occur.

If the single element is less active, then no reaction will occur.

3. Write a skeleton equation a. write ionic formula’s correctly (neutral)

b. if a transition metal’s charge is not told to you, assume that it has the same charge as the ion it replaces.

4. Balance the equation.

Predicting and Writing Equations for Single Replacement Rxns Predict whether silver solid will react with a Nickel II chloride solution.

Write the equation to show the reaction , or write the reactants followed by "no reaction".


AcidBase Reactions Acid = H+ ion donor Base = H+ acceptor

H+ acceptor H+ donor

BronstedLowry Definition of Acids and Bases


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Acid = electron pair acceptor Base = electron pair donor

** unless otherwise noted, we will be using the bronsted/lowry definition of acids and bases throughout the rest of the presentation.

Lewis Definition of Acids and Bases Acid/Base Reactions

Bronsted/Lowry Acid/Base reactions involve the transfer of H+ ions from one an acid (H+ donor) to a base (H+ acceptor)

Example: HC2H3O2(aq) + CO32(aq) > HCO3(aq) + C2H3O2(aq)

HC2H3O2(aq) gave away it's H+ = acid

CO32(aq) accepted an H+ = base

Acid/Base Reactions

Identify the acid and base in the following reaction:

CN + H2O > HCN + OH

CN accepted an H+ so it is a base

H2O donated an H+ so it is an acid

Identify the acid and base in the following reaction:

HCO3 + HF > F + H2CO3

HCO3 accepted an H+ so it was a base

HF donated an H+ so it was an acid

move for answer

Acid/Base Reactions


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January 10, 2019

Neutralization reactions are a special type of acid/base reaction in which an acid and base react to produce water.

Example: HF + OH > H2O + F

Neutralization Reactions 32 Which of the following acid/base reactions represent a neutralization reaction?

A H+ + CN > HCNB HNO2 + OH > H2O + NO2C HCN + NH3 > NH4+ + CND HCO3 + H2O > CO32 + H3O+E none of these

answ

er

The classic childhood reaction of vinegar (HC2H3O2) and baking soda (HCO3) is an acid/base

reaction.

Which molecule is the conjugate base of acetic acid (HC2H3O2)?

C2H3O2answer

Real World Application

HC2H3O2(aq) + HCO31(aq) > C2H3O2

1(aq) + CO2(g) + H2O(l)


Identifying Reaction Types


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January 10, 2019

Identifying what kind of reaction it is?

1) Does the reaction produce an insoluble solid? Precipitation Reaction

2) Are H+ ions are being transferred? Acid/base reaction

3) Do you have only 1 reactant? Decomposition Reaction

4) Is there only 1 product? Combination / Synthesis Reaction

5) Is O2 a reactant? Combustion Reaction

6) Does an element react with a compound? Single Replacement Rxn

7) Check oxidation states..Is the same element being oxidized AND reduced? Disproportionation Reaction.

What kind of reaction it is?What kind of reaction is the following?

C4H8(s) + O2(g) > CO2(g) + H2O(g)

33 Which of the following would be an example of an oxidation/reduction reaction?

A CH3COOH + NH3 > NH4+ + CH3COOB AlCl3(s) > Al3+(aq) + 3Cl(aq)C 2Ag+(aq) + Cu(s) > Cu2+(aq) + 2Ag(s)D H+(aq) + OH(aq) > H2O(l)E Zn2+(aq) + CO32(aq) > ZnCO3(s)

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Mg2+(aq) + 2OH(aq) > Mg(OH)2(s)

1. Are you forming a precipitate? Yes .... Precipitationmove for answer

What kind of reaction it is?


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34 Which of the following is NOT an acid/base reaction?

A H2O + CN > OH + HCNB 2CuO >2Cu + O2

C NH3 + HSO4 > NH4+ + SO42

D H+ + OH > H2OE All of these are acid/base reactions

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Predicting Products and Completing Equations

Precipitation Reactions: switch the cation anion partners in the reactants to form two ionic products.

* be sure to write neutral formulas.

Ex: AgNO3 (aq) + BaCl2 (aq) > AgCl(s) + BaNO3(aq)

Predicting Products of Synthesis Reactions

For a combination of a metal with a nonmetal: determine the common ions of the elements and write a neutral formula for an ionic compound.

Ex: Ca + 2F > CaF2

Ca2+ F1

Predicting Products of Synthesis Reactions

For a reaction between two nonmetals: Remember that

atoms want a full octet and will make one bond for every electron they need.

N2 + 3H2 > 2NH3


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Predicting Products of Combustion Reactions

Combustion of a hydrocarbon always produces CO2 and H2O.

C2H4 + 3O2 > 2CO2 + 2H2O

Predicting Products of Decomposition Reactions

Products of decomposition reactions can be considered to be the component pure elements if not told otherwise.

2H2O > 2H2 + O2

Characteristics of Chemical Reactions

The Collision theory of chemical reactions states that the energy needed to break bonds to initiate a chemical reaction comes from the kinetic energy of the reactant particles as they collide with each other.

• Not all collisions result in a chemical reaction. If the colliding particles do not have enough KE to break the bonds, the original molecules simply bounce off one another and maintain their original form.

Energy in Chemical Reactions


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Activation Energy

Activation Energy, Ea , is the minimum amount of energy needed to be input in order for a reaction to occur.

• It comes from the collision of particles.

• For an individual collision to result in a reaction, the particles must collide effectively in that they must1. Have enough kinetic energy (greater than the

activation energy, Ea)2. Collide in the proper orientation

• The rate of a reaction depends on the frequency of effective collisions

Law of Conservation of Energy: Energy is neither created or destroyed, just transferred from one form to another during a chemical reaction. Total energy in a system is conserved…Any energy lost by reactants is absorbed by the surroundings.

Energy absorbed by reactants is taken from the surroundings.

Law of Conservation of Energy Exothermic and Endothermic Reactions

Exothermic reactions: release energy (often heat) to the surroundings.

* the container will feel warm

* the products will have less stored energy (chemical potential energy) than the reactants.


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Exothermic and Endothermic Reactions

Endothermic reactions: absorb energy (often heat) from the surroundings.

* the container will feel cool

* the products will have more stored energy (chemical potential energy) than the reactants.

• In an endothermic reaction, the reacting molecules absorb energy causing the products to have a higher chemical potential energy than the reactants.

• In an exothermic reaction, the reacting molecules release energy to the surroundings, causing products with a lower chemical potential energy compared to the original reactant molecules.

Six conditions affect the rate of a reactionThe rate (or speed) of a reaction depends on:

1. The reactants themselves

2. Temperature

3. Presence of a catalyst

4. Concentration of reactants and products

5. Pressure of a gaseous reactant

6. Size of the particles

Effect of type of substance and Temperature on Reaction Rate

1. Nature of the reactants – how a substance reacts is part of its chemical properties.

2. Temperature – Raising temperature will generally increase the rate of the chemical reaction due to the increased rate of KE of the particles leading to increased number of collisions.

• Generally a 10oC rise in temperature will approximately double the rate of the reaction


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Effect of a Catalyst on Reaction RateCatalysts increase the rate of reaction without being used up. They do this by lowering the activation energy needed. With a catalyst, more collisions result in a reaction, so the rate of reaction increases. Different reactions need different catalysts.

Effect of Concentration on Reaction RateIncreasing concentration of reactants in solution will increase the rate of reaction.

Decreasing concentration of reactants in solution will slow the rate of reaction.

Effect of particle size on reaction rateWhen a solid reacts with a gas or a substance in solution, collisions occur only at the surface of the solid. If you increase surface area by making the solid particles smaller, you will increase the rate of the reaction.


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An alarming example of the effect of particle size is a coal dust explosion in a mine. The small sized coal dust, set off by a spark, reacts almost instantly with oxygen. Lump coal will burn slowly and must be kindles to get it to start burning in the first place.

Coal dust vs Lump Coal Reaction

https://www.youtube.com/watch?v=Vkqj8aLQ8EM

Chemical EquilibriumMany chemical reactions are reversible, and the forward and backward reactions can occur at the same time. When the rate of the forward reaction is equal to the rate of the backward reaction, we call that a dynamic equilibrium.

• The rate of change forward and backwards are the same, but the concentrations of the reactants and products are NOT necessarily equal.

https://www.youtube.com/watch?v=Vkqj8aLQ8EM


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Chemical EquilibriumLe Chatelier's Principle

Le Chatlier's principle (also known as "Chatelier's principle" or "The Equilibrium Law") states that when a system experiences a disturbance (such as concentration, temperature, or pressure changes), it will respond to restore a new equilibrium state. For example, if more reactants are added to a system, Le Chatlier's principle predicts that the reaction will generate more products to offset the change and restore equilibrium.

• Adding more reactants will cause an increase in the forward reaction.

• Adding more product will cause an increase in the reverse reaction.

• Removing product will cause an increase in the forward reaction.

Le Chatelier's Principle


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table of contents: chemical reactions - gcit.enschool.org · chemical reactions notes jan 10 3...

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