Chemical ReactionsPOPS Chemistry Unit 4

• What is a chemical reaction• What are the different types

chemical reactions• How to balance a chemical

reaction • Oxidation/ Reduction

Reactions• Acid and bases reactions• Applications

What is a chemical Reaction? • What is a chemical reaction• What are the different types chemical reactions• How to balance a chemical reaction • Oxidation/ Reduction Reactions• Acid and bases reactions• Applications

Chemical ReactionsOccur when bonds are formed

and broken causing substances to recombine into different substances◦Reactants = starting substances◦Products = ending substances◦Arrow always points to the products Ex: H2 + O2 2H2O

Some Reactions in Progress!

Example of Chemical Reactions

Zn + 2 HCl → ZnCl2 + H2

What are the reactants?Zn and HCl

What are the products?ZnCl2 and H2

How do you know when a chemical reaction takes

place?

Color Change Precipitate Formation

A chemical change: any change in which a new substance is formed.

Evidence of a Chemical Change: Release of energy as heat Release of energy as light Change in color Formation of a gas Change in odor…

Chemical Reactions

Meanings of some symbols

What is a chemical Reaction? • What is a chemical reaction

• What are the different types chemical reactions

• How to balance a chemical reaction • Oxidation/ Reduction Reactions• Acid and bases reactions• Applications

Type of Reaction

Definition Equation

Synthesis

Decomposition

Single Replacement

Double Replacement

Watch the movie and then complete the chart.

A = Red B = Blue C = Green D = Yellow

A + B → AB

AB → A + B

AB + C → AC + B

AB + CD → AC + BD

Two or more elements or compounds combine to make a more complex

substance

Compounds break down into simpler substances

Occurs when one element replaces another one in a

compound

Occurs when different atoms in two different

compounds trade places

Identifying Chemical Reactions

____ P + O2 → P4O10 ____ Mg + O2 → MgO

____ HgO → Hg + O2 ____ Al2O3 → Al + O2

____ Cl2 + NaBr → NaCl + Br2 ____ H2 + N2 → NH3

2. Use colored pencils to circle the common atoms or compounds in each equation to help you determine the type of reaction it illustrates. Use the code below to classify each reaction.

S = Synthesis D = Decomposition SR = Single Replacement DR = Double Replacement

 

____ Na + Br2 → NaBr ____ CuCl2 + H2S → CuS + HCl 

____ HgO + Cl2 → HgCl + O2 ____ C + H2 → CH4

 

____ KClO3  →   KCl  +  O2  ____ S8 + F2 → SF6

 

____ BaCl2   +   Na2 SO4 →     NaCl   +   BaSO4

What is a combustion A combustion reaction is a type of reaction in which a

combustible material combines and generates heat (exothermic reaction).

The reactants are almost always a hydrocarbon and oxygen and the products are almost always carbon dioxide and water

General Form of a Combustion Reaction hydrocarbon + oxygen → carbon dioxide + water

ExampleC10H8 + 12 O2 → 10 CO2 + 4 H2O

You Try 1. methane (CH4) + oxygen

2. ethane (C2H6) + oxygen

 3. propane (C3H8) + oxygen

4. butane (C4H10) + oxygen

Chemical Reactions • What is a chemical reaction• What are the different types chemical reactions

• How to balance a chemical reaction

• Oxidation/ Reduction Reactions• Acid and bases reactions• Applications

Law of conservation of Matter

States the matter cannot be created nor destroyed.

This means that the number of atoms of each type must be the same in the products and the reactants.

This means that chemical equations must be balanced.

Balancing Equations

i.Subscript: # of atoms in that molecule (small #) – cannot change to balance equation

ii.Coefficient: # of molecules you have (large #)1.Ex: 2H2 + O2 2H2O

Subscript

Coefficient

So there are 2 molecules of 2 hydrogens reacting with 1 molecule of two oxygen to form 2 molecules of water.

-Notice that the atoms and the number of atoms are the exact same on both sides.

Steps to Balancing an Equation

1. Write all reactants on the left and all products on the right side of the equation arrow. Make sure you write the correct formula for each element.

2. Make a list below both the reactants and the products and list all of the atoms in each element in the equation. Determine if the equation is balanced or not. If it is a balanced equation, it has the same number of atoms of each element on both sides of the arrow. If the equation does not have the same number of atoms of element on both sides of the arrow, then it is not balanced.

3. Use coefficients in front of each formula to balance the number of atoms on each side. Be sure to change the number of atoms in the list below.

4. Multiply the coefficient of each element by the subscript of the element to count the atoms. Then list the number of atoms of each element on each side.

5. It is often easiest to start balancing with an element that appears only once on each side of the arrow. These elements must have the same coefficient. Next balance elements that appear only once on each side but have different numbers of atoms. Finally balance elements that are in two formulas in the same side.

Example of how to balance an equation

Start with an equation.

Mg + O2 MgO

Then all you do is list the atoms that are involved on each side of the arrow

Mg + O2 MgOMgO

MgO

[1] Just count up the atoms on each side

Then start balancing:

Mg + O2 MgOMg

O

1

1

1

2

[2] The numbers aren’t balanced so then add “BIG” numbers to make up for any shortages

And adjust totals

Mg + O2 MgOMg

O

1

1

1

2

2

2

2

Mg + O2 MgOMg

O

1

2

2

2

2

But the numbers still aren’t equal, so add another “BIG” number

2

And adjust totals again

NOW BOTH SIDES HAVE EQUAL NUMBERS OF ATOMS

WE SAY THAT THE EQUATION IS BALANCED!!

2

Try to balance these equations using the same method:

[1] Na + Cl2 NaCl

[2] CH4 + O2 CO2 + H2O

[4] Al + O2 Al2O3

[3] Li + HNO3 LiNO3 + H2

How did you get on??

[1] 2 Na + Cl2 2 NaCl

[2] CH4 + 2 O2 CO2 + 2 H2O

[4] 4 Al + 3 O2 2 Al2O3

[3] 2 Li + 2 HNO3 2 LiNO3 + H2

Here are the answers:

Chemical Reactions • What is a chemical reaction• What are the different types chemical reactions• How to balance a chemical reaction

• Oxidation/ Reduction Reactions

• Acid and bases reactions• Applications

25

Oxidation reactions are always accompanied by a reduction reaction

Oxidation -    originally meant combining with oxygen-    iron rusting (iron + oxygen)  Reduction -    originally meant the loss of oxygen from a compoundremoving iron from iron ore ( iron II oxide)

26

20.2 Electron Transfer in Redox Reactions  Today

OXIDATION means:-    a complete or partial LOSS of ELECTRONS REDUCTION means:-    a complete or partial GAIN of ELECTRONS Memory Device :

LEO the lion says GER or OIL RIG

27

The substance that donates electrons in a redox reaction is the REDUCING AGENT 

The substance that takes electrons in a redox reaction is the OXIDIZING AGENT

28

Oxidation is…

– the loss of electrons

– an increase in oxidation state

– the addition of oxygen

– the loss of hydrogen

2 Mg + O2 ® 2 MgO

notice the magnesium is losing electrons

Reduction is…

– the gain of electrons

– a decrease in oxidation state

– the loss of oxygen

– the addition of hydrogen

MgO + H2 ® Mg + H2O

notice the Mg2+ in MgO is gaining electrons

1) 2 Na + FeCl2 2 NaCl + Fe   2) 2 C2H2 + 5 O2 4 CO2 + 2 H2O  

 3) 2 PbS + 3 O2 2 SO2 + 2 PbO 

Let’s Practice

How did you do? 1) 2 Na + FeCl2 2 NaCl + Fe

 Sodium is oxidized, going from a 0 to +1 oxidation state.Iron is reduced, going from a +2 to 0 oxidation state.  2) 2 C2H2 + 5 O2 4 CO2 + 2 H2O

 Carbon is oxidized, going from a –1 to +4 oxidation state.Oxygen is reduced, going from a 0 to –2 oxidation state.  3) 2 PbS + 3 O2 2 SO2 + 2 PbO

 Sulfur is oxidized, going from a –2 to +4 oxidation state.Oxygen is reduced, going from a 0 to –2 oxidation state. 

Chemical Reactions • What is a chemical reaction• What are the different types chemical reactions• How to balance a chemical reaction • Oxidation/ Reduction Reactions

• Acid and bases reactions• Applications

What is an acid?An acid is a solution that has an

excess of H+ ions. It comes from the Latin word acidus that means "sharp" or "sour".

The more H + ions, the more acidic the solution.

Properties of an AcidTastes SourConduct ElectricityCorrosive, which means

they break down certain substances. Many acids can corrode fabric, skin, and paper

Some acids react strongly with metals

Turns blue litmus paper red

Picture from BBC Revision Bites http://www.bbc.co.uk/schools/ks3bitesize/science/chemistry/acids_bases_1.shtml

Uses of Acids Acetic Acid = VinegarCitric Acid = lemons,

limes, & oranges. It is in many sour candies such as lemonhead & sour patch.

Ascorbic acid = Vitamin C which your body needs to function.

Sulfuric acid is used in the production of fertilizers, steel, paints, and plastics.

Car batteries

What is a base?A base is a solution

that has an excess of OH- ions.

Another word for base is alkali.

Bases are substances that can accept hydrogen ions

Properties of a BaseFeel SlipperyTaste BitterCorrosiveCan conduct

electricity. (Think alkaline batteries.)

Do not react with metals.

Turns red litmus paper blue.

Uses of BasesBases give soaps,

ammonia, and many other cleaning products some of their useful properties.

The OH- ions interact strongly with certain substances, such as dirt and grease.

Chalk and oven cleaner are examples of familiar products that contain bases.

Your blood is a basic solution.

pH ScalepH is a measure of how

acidic or basic a solution is.• The pH scale ranges from 0

to 14. Acidic solutions have pH

values below 7A solution with a pH of 0 is

very acidic.A solution with a pH of 7 is

neutral.• Pure water has a pH of 7. • Basic solutions have pH

values above 7.

pH Scale

• A change of 1 pH unit represents a tenfold change in the acidity of the solution.

• For example, if one solution has a pH of 1 and a second solution has a pH of 2, the first solution is not twice as acidic as the second—it is ten times more acidic.

Acid – Base Reactions

A reaction between an acid and a base is called neutralization. An acid-base mixture is not as acidic or basic as the individual starting solutions.

Neutralization Reactions An acid base reaction often

produces water and salt. The general form of a acid base reaction is

Acid + Base Salt +water

Example

HCl + NaOH NaCl + H20

Each salt listed in this table can be formed by the reaction between an acid and a base. Can you guess which acids and bases were the reactants?

Chemical Reactions • What is a chemical reaction• What are the different types chemical reactions• How to balance a chemical reaction • Oxidation/ Reduction Reactions• Acid and bases reactions

• Applications

Some Important Equations To Know

Equation for Photosynthesis6CO2 + 6H2O Light

Chlorophyll C6H12O6 +6O2

Equation for Cell RespirationC6H12O6 +6O2 6CO2 + 6H2O +Energy +Heat

Chemical reactions happen when

a car is startedtarnish is removed from silverfertilizer is added to help plants

growfood is digestedelectricity is produced from

burning natural gasrust is formed on iron nails

Everything in our lives from materials to life involve chemistry

glass (SiO2)n

metal alloyschemically treated waterplastics and polymersbaking soda, NaHCO3

foods fertilizers and pesticidesliving beings

Chemicals in Toothpaste

Chemistry is Cool!