1 ib topic 1: quantitative chemistry 1.3: chemical equations 1.3.1 deduce chemical equations when...

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IB Topic 1: Quantitative Chemistry1.3: Chemical Equations

1.3.1 Deduce chemical equations when all reactants and products are given

1.3.2 Identify the mole ratio of any two species in a chemical reaction.

1.3.3 Apply the state symbols (s), (l), (g) and (aq)

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1.3.1 Deduce chemical equations when all reactants and products are given.

What is a chemical reaction?Rearrangement of atoms forming new substancesReactants Products

Some reactions are desirable…Glucose + oxygen Carbon dioxide + water

…some are not.Iron + oxygen iron (III) oxide

(a.k.a. rust)

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Chemical Reactions

A few ways to determine whether a chemical reaction has taken place: Heat is absorbed or given off Change in color Change in odor Production of a gas or solid

(precipitate) Not easily reversible (it won’t

recreate the reactants)

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Chemical formulas are easier and more informative to use in equations than words.

A skeleton equation is a chemical equation that shows what reactants and products are involved. It does not necessarily indicate the relative amounts of reactants and products.

Fe + O2 Fe2O3

Sometimes the skeleton equation is balanced (all coefficients = 1).

SnO2(s) Sn(s) + O2(g)

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Identify types of chemical reactions

Types of Chemical Reactions

1) Synthesis or Combination Reaction: Two or more substances combine to form a single substance.

2Na(s) + Cl2(g) 2NaCl(s) CaO(s) + H2O(l) Ca(OH)2(aq) 2H2(g) + O2(g) 2H2O (l) 4Fe(s) + 3O2(g) 2Fe2O3(s) N2(g) + 3H2(g) 2NH3(g)

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2) Decomposition Reactions: A single substance is broken down into two or more substances.

CaCO3(s) CaO(s) + CO2(g) 2H2O(l) 2H2(g) + O2(g) 2H2O2(aq) 2H2O(l) + O2(g)

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3) Single-Replacement Reactions: One element replaces another in a compound.

Mg(s) + Zn(NO3)2(aq) Mg(NO3)2(aq) + Zn(s) 2K(s) + 2H2O(l) 2KOH (aq) + H2(g) Cu(s) + 2AgNO3(aq) Cu(NO3)2(aq) + 2Ag(s) 2Al(s) + Fe2O3(s) Al2O3(s) + 2Fe(s) Cl2(g) + 2NaBr(aq) 2NaCl(aq) + Br2(g)

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4) Double-Replacement Reactions: Ions of two reacting compounds trade places.

Na2CO3(aq) + CaCl2(aq) CaCO3(s) + 2NaCl(aq) Na2S(aq) + Cd(NO3)2(aq) CdS(s) + 2NaNO3(aq) NaOH(aq) + HCl(aq) NaCl(aq) + H2O(l) H2SO4(aq) + 2NaCN(aq) Na2SO4(aq) +

2HCN(g)

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5) Combustion Reactions: A compound reacts with oxygen. Products are usually carbon dioxide and water.

CH4(g) + O2(g) CO2(g) + H2O(g) C3H8(g) + 5O2(g) 3CO2(g) + 4H2O(g) 2C8H18(l) + 25O2(g) 16CO2(g) + 18H2O(g) C2H5OH(l) + 3O2(g) 2CO2(g) + 3H2O(g)

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Balancing chemical equations

The Law of Conservation of Matter: In a chemical (non-nuclear) reaction, atoms are neither created nor destroyed.

For an equation to be balanced the number of atoms of each element is the same on both sides of the equation.H2(g) + O2(g) H2O (l) (unbalanced)2H2(g) + O2(g) 2H2O (l) (balanced)

K(s) + H20(l) KOH (aq) + H2(g) (unbalanced)2K(s) + 2H20(l) 2KOH (aq) + H2(g) (balanced)

C6H12O6 + O2 CO2 + H2O (unbalanced)C6H12O6 + 6O2 6CO2 + 6H2O (balanced)

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Counting Atoms

Subscripts indicate how many of a specific atom is present in a compound This is the small number to the bottom right of an

element in a compound. Ex. H2O… 2 is the subscript

Coefficients tell us how many units of the compound we have Ex. 3 H2O means that we have 3 water molecules So, how many hydrogen atoms do we have?

Oxygen atoms? Let’s practice

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Rules for Balancing Equations

1) Write the correct formulas for the reactants on the left side of the yield sign and products on the right side.

2) Count the number of atoms of each element in the products and the reactants.

3) Balance the elements one at a time by using coefficients. Do not change the subscripts in the chemical formulas.

4) Check each atom or polyatomic ion to make sure the equation is balanced.

5) Make sure all coefficients are in the lowest possible ratio.

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N2 + H2 NH3

1) Formulas given

2) Reactants Products2N 2H 1N 3H

3) Balance N by putting 2 in front of NH3

N2 + H2 2NH3

Balance H by putting 3 in front of H2

N2 + 3H2 2NH3

4) 2N 6H 2N 6H

5) Lowest ratio of coefficients

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KClO3 KCl + O2

1) Formulas given2) Reactants Products

1K 1Cl 3O 1K 1Cl 2O3) Balance O by putting 2 in front

of KClO3

and 3 in front of O2

2KClO3 KCl + 3O2

Balance K & Cl by putting 2 in front of KCl

2KClO3 2KCl + 3O2

4) 2K 2Cl 6O 2K 2Cl 6O5) Lowest ratio of coefficients

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Balance the following equations

Fe(s) + O2(g) Fe2O3(s)

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

Al(s) + Fe2O3(s) Al2O3(s) + Fe(s)

H2SO4(aq) + NaCN(aq) Na2SO4(aq) + HCN(g)

C2H5OH(l) + O2(g) CO2(g) + H2O(g)

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Balance the following equations

4Fe(s) + 3O2(g) 2Fe2O3(s)

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

2Al(s) + Fe2O3(s) Al2O3(s) + 2Fe(s)

H2SO4(aq) + 2NaCN(aq) Na2SO4(aq) + 2HCN(g)

C2H5OH(l) + 3O2(g) 2CO2(g) + 3H2O(g)

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Aluminum bromide + chlorine yield aluminum chloride + bromine

2AlBr3 + 3Cl2 2AlCl3 + 3Br2

Seven elements are diatomic: H2, N2, O2, F2, Cl2, Br2, I2

Copper + oxygen produces copper(I) oxide4Cu + O2 2Cu2O

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Sodium chlorate decomposes to sodium chloride and oxygen gas

Aluminum nitrate plus sodium hydroxide yields aluminum hydroxide plus sodium nitrate

Ethane (C2H6) burns in oxygen to produce

carbon dioxide and water vapor

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Sodium chlorate decomposes to sodium chloride and oxygen gas

2NaClO3 2NaCl + 3O2

Aluminum nitrate plus sodium hydroxide yields aluminum hydroxide plus sodium nitrate

Al(NO3)3 + 3NaOH Al(OH)3 + 3NaNO3

Ethane (C2H6) burns in oxygen to produce

carbon dioxide and water vapor2C2H6 + 7O2 4CO2 + 6H2O

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Symbols used in chemical reactions

+ Used to separate two reactants or products

A “Yields” arrow () separates products from reactants Used in place of for reversible reactions(s) Designates a solid reactant or product(l) Designates a liquid reactant or product(g) Designates a gaseous reactant or product(aq) Designates an aqueous reactant or product Indicates that heat is supplied to the reaction

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(s) Designates a solid reactant or product(l) Designates a liquid reactant or product(g) Designates a gaseous reactant or product(aq) Designates an aqueous reactant or product

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Rule 1. All compounds of Group IA elements (the alkali metals) are soluble.

For example, NaNO3, KCl, and LiOH are all soluble compounds. This means that an aqueous solution of KCl really contains the predominant species K+ and Cl- and, because KCl is soluble, no KCl is present as a solid compound in aqueous solution:KCl(s) => K+

(aq.) + Cl-(aq.)

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Rule 2. All ammonium salts (salts of NH4+)

are soluble.

For example, NH4OH is a soluble compound. Molecules of NH4OH completely dissociate to give ions of NH4

+ and OH- in aqueous solution.

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Rule 3. All nitrate (NO3-), chlorate (ClO3

-), perchlorate (ClO4

-), and acetate (CH3COO- or C2H3O2

- are soluble.

For example, KNO3 would be classified as completely soluble by rules 1 and 3. Thus, KNO3 could be expected to dissociate completely in aqueous solution into K+ and NO3

- ions: KNO3 => K+(aq.) + NO3-

(aq.)

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Rule 4. All chloride (Cl-), bromide (Br-), and iodide (I-) salts are soluble except for those of Ag+, Pb2+, and Hg2

2+.

For example, AgCl is a classic insoluble chloride salt: AgCl(s) <=> Ag+

(aq.) + Cl-(aq.)

(Ksp = 1.8 x 10-10).

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Rule 5. All sulfate ( SO4=) compounds are soluble

except those of Ba2+, Sr2+, Ca2+, Pb2+, Hg22+, and

Hg2+. Ca2+ and Ag+ sulfates are only moderately soluble.

For example, BaSO4 is insoluble (only soluble to a very small extent):BaSO4(s) <=> Ba2+

(aq.) + SO42-

(aq.)

(Ksp = 1.1 x 10-10). Na2SO4 is completely soluble:Na2SO4(s) => 2 Na+

(aq.) + SO42-

(aq.).

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Rule 6. All hydroxide (OH-) compounds are insoluble except those of Group I-A (alkali metals) and Ba2+, Ca2+, and Sr2+.

For example, Mg(OH)2 is insoluble

(Ksp = 7.1 x 10-12)NaOH and Ba(OH)2 are soluble, completely dissociating in aqueous solution:NaOH(s) => Na+(aq.) + OH- (aq.), a strong baseBa(OH)2(s) => Ba2+ (aq.) + 2OH- (aq.)

(Ksp = 3 x 10-4)

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Rule 7. All sulfide (S2-) compounds are insoluble except those of Groups I-A and II-A (alkali metals and alkali earths).

For example, Na2S(s) <=> 2Na+ (aq.) + S2- (aq.)MnS is insoluble (Ksp = 3 x 10-11).

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Rule 8. All sulfites (SO32-), carbonates

(CO32-), chromates (CrO4

2-), and phosphates (PO4

3-) are insoluble except for those of NH4

+ and Group I-A (alkali metals)(see rules 1 and 2).

For example, calcite, CaCO3 (s) <=> Ca2+ (aq.) + CO3

2- (aq.)

(Ksp = 4.5 x 10-9).

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OR... Use a Solubility Chart Let’s use the following reactions to apply this

assessment statement

1. Hydrogen peroxide decomposes into water and oxygen gas

2. Potassium phosphate reacts with magnesium chloride to form magnesium phosphate and potassium chloride

3. Iron reacts with copper (II) sulfate to form iron (II) sulfate and copper

4. Sulfuric acid (hydrogen sulfate) reacts with copper (II) oxide to produce copper (II) sulfate and water

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1. Hydrogen peroxide decomposes into water and oxygen gas

2 H2O2(aq) 2 H2O(l) + O2(g) 2. Potassium phosphate reacts with magnesium chloride

to form magnesium phosphate and potassium chloride

2K3PO4 (aq) + 3MgCl2 (aq) Mg3(PO4)2 (s) + 6KCl (aq)3. Iron reacts with copper (II) sulfate to form iron (II)

sulfate and copperFe(s) + CuSO4(aq) FeSO4(aq) + Cu(s)

4. Sulfuric acid (hydrogen sulfate) reacts with copper (II) oxide to produce copper (II) sulfate and waterH2SO4 (aq) + CuO (s) CuSO4 (aq) + H2O (l)

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Cookies and Chemistry…Huh!?!? Just like chocolate chip

cookies have recipes, chemists have recipes as well

Instead of calling them recipes, we call them reaction equations

Furthermore, instead of using cups and teaspoons, we use moles

Lastly, instead of eggs, butter, sugar, etc. we use chemical compounds as ingredients

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Coefficients are in particles or in moles2 f.u. NaClO3 2 f.u. NaCl + 3 molecules O2

2 mol NaClO3 2 mol NaCl + 3 mol O2

We will use moles because we measure moles in grams

The coefficients give us mole ratios

Mole ratio NaClO3:NaCl is 2:2

Mole ratio NaCl:O2 is 2:3

Mole ratio O2:NaCl is 3:2

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Consider the following equation2K2Cr2O7 + 2H2O + 3S 4KOH + 2Cr2O3 + 3SO2

What is the KOH:S mole ratio?What is the K2Cr2O7:Cr2O3 mole ratio?

What is the mole ratio between sulfur dioxide and water?

What species will give mole ratios of 4:2?

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Consider the following equation2K2Cr2O7 + 2H2O + 3S 4KOH + 2Cr2O3 + 3SO2

What is the KOH:S mole ratio? 4:3What is the K2Cr2O7:Cr2O3 2:2What is the mole ratio between sulfur dioxide and water?

3:2What species will give mole ratios of 4:2?

KOH:K2Cr2O7 KOH:H2O KOH:Cr2O3

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Looking at a reaction tells us how much of something you need to react with something else to get a product (like the cookie recipe)

Be sure you have a balanced reaction before you start!

Example: 2 Na + Cl2 2 NaCl This reaction tells us that by mixing 2 moles of

sodium with 1 mole of chlorine we will get 2 moles of sodium chloride

What if we wanted 4 moles of NaCl? 10 moles? 50 moles?

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These mole ratios can be used to calculate the moles of one chemical from the given amount of a different chemical

Example: How many moles of chlorine is needed to react with 5 moles of sodium (without any sodium left over)?

2 Na + Cl2 2 NaCl

5 moles Na 1 mol Cl2

2 mol Na= 2.5 moles Cl2

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Looking at a reaction tells us how much of something you need to react with something else to get a product (like the cookie recipe)

Be sure you have a balanced reaction before you start!

Example: 2 Na + Cl2 2 NaCl This reaction tells us that by mixing 2 moles of

sodium with 1 mole of chlorine we will get 2 moles of sodium chloride

What if we wanted 4 moles of NaCl? 10 moles? 50 moles?

How many moles of sodium chloride will be produced if you react 2.6 moles of chlorine gas with an excess (more than you need) of sodium metal?

2 Na + Cl2 2 NaCl

2.6 moles Cl2 2 mol NaCl

1 mol Cl2= 5.2 moles NaCl


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1.3.2 Practice Write the balanced reaction for hydrogen gas

reacting with oxygen gas. 2 H2 + O2 2 H2O

How many moles of reactants are needed? What if we wanted 4 moles of water? What if we had 3 moles of oxygen, how much hydrogen

would we need to react and how much water would we get?

What if we had 50 moles of hydrogen, how much oxygen would we need and how much water produced?

2 mol H2 1 mol O2

4 mol H2

2 mol O2

6 mol H2, 6 mol H2O

25 mol O2, 50 mol H2O

1 ib topic 1: quantitative chemistry 1.3: chemical equations 1.3.1 deduce chemical equations when...

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