Balancing Chemical ReactionsConsider the reaction: magnesium burns in oxygen (in the air) to produce magnesium oxide powder:

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

Look at the total number of "O" atoms on the reactant side compared to the total number of "O" atoms on the product side. As it stands now, it looks like we DESTROYED an "O" atom. Yet: A chemical reaction cannot create or destroy atoms!

THE LAW OF CONSERVATION OF MASS:Matter cannot be created or destroyed in a chemical reaction; thus the total mass of the reactants is ALWAYS equal to the total mass of the products.

So far, our reactions have been UNBALANCED; we have just written the skeleton equations - "bare bones" chemical equations with the CORRECT formulas, but the AMOUNTS of atoms are unbalanced.

We must BALANCE our skeleton equations to make them obey the law of conservation of mass.Key Ideas:

- reactants are on the left of the arrow; products on the right.- Watch out for the "7-Up" diatomic elements. When you see a substance described as

"oxygen", with no other element in that substance, then it is "O2", not just "O". The "7-Up club" are: nitrogen (N2), oxygen (O2), fluorine (F2), chlorine (Cl2), bromine (Br2), iodine (I2), and hydrogen (H2). Also watch out for just "sulfur" which is "S8" and "phosphorus" which is "P4". Also remember that when these elements are with another element in a compound, we go by the name of the compound to write the formula. So "nickel(III) fluoride" is NiF3, which is different from just "fluorine", which is "F2".

- For the states of chemicals, a chemical is:- a solid, (s), for the common descriptive words as powder, precipitate, foil. "Metal"

implies a solid, under usual lab conditions.- a gas, (g) for the common descriptive word of vapour.- an aqueous solution, (aq), for the descriptive words of solution, dissolved

If there is no description of the state of the chemical, the state can be omitted- "yields" means "produces".

BALANCING CHEMICAL REACTIONSStep 1: If not given, write a skeleton equation - the correct formulas.Step 2: Look for ONE element in the equation that is UNBALANCED between left and right;

BALANCE it by PLACING A NUMBER IN FRONT of the WHOLE FORMULA; thenRECHECK the balance until ALL atoms are balanced.(Helpful hint: Watch out for polyatomic ions. If they stay together as a group between the left and right side, balance the polyatomic ions as a group.)Final note: MAKE SURE YOUR BALANCING IS IN LOWEST TERMS.

Write a complete balanced equation for the following.

(a) _____Al(s) + _____KCl(s) _____AlCl3(s) + _____K(s)

(b) _____CoCl3(aq) + _____AgNO3(aq) _____AgCl(s) + _____Co(NO3)3(aq)

(c) _____H2O2(aq) _____O2(g) + _____H2O(l)

Balancing Chemical Equations, Sheet 2

ANSWER KEY

From Word Equations to Balanced Chemical Equations"Word Equations" Review

Practice Problems: Write balanced chemical equations for each of the following.

(a) iron(III) bromide solution + oxygen gas iron(III) oxide precipitate + bromine liquid

(b) potassium metal + iodine vapour potassium iodide powder

(c) lead(II) nitrate solution + sodium fluoride solution lead(II) fluoride precipitate+ aqueous sodium nitrate

(d) When heated, zinc metal reacts with phosphorus powder to produce solid zinc phosphide.

(e) Sulfur reacts with chlorine gas to produce sulfur dichloride liquid.

(f) Hydrogen peroxide solution decomposes into liquid water and oxygen gas in the presence of MnO2 catalyst.

Answers(a) 4 FeBr3(aq) + 3 O2(g) 2 Fe2O3(s) + 6 Br2(l)(b) 2 K(s) + I2(g) 2KI(s)(c) Pb(NO3)2(aq) + 2 NaF(aq) PbF2(s) + 2 NaNO3(aq)

(d) 6 Zn(s) + P4(s) 2 Zn3P2(s)(e) S8(s) + 8 Cl2(g) 8 SCl2(l)

MnO2

(f) 2 H2O2(aq) 2 H2O(l) + O2(g)

Our goal: Given a chemical reaction, expressed in the names of the chemical reactants and products, we want to:

- write the chemical formula of each substance first;- balance the chemical reaction.

Write complete balanced chemical equations for each of the following. If descriptions of the states of matter ( (s), (l), (g), (aq) ) are included, then included the states of matter. Otherwise the states of matter are not required.Sample Problem:Write balanced chemical equations for each of the following:(a) magnesium metal + oxygen gas magnesium oxide powder

(b) Copper(II) chloride solution reacts with aluminum foil to yield a solution of aluminum chloride and copper powder precipitate.

1. Solid zinc metal + lead(II) nitrate solution produces zinc nitrate solution + lead metal

2. aluminum bromide powder + chlorine gas produces aluminum chloride powder + bromine liquid

3. aqueous sodium phosphate + aqueous calcium chloride yield calcium phosphate precipitate+ sodium chloride solution

4. solid potassium chlorate, when heated, yields solid potassium chloride and oxygen gas

5. aluminum metal + hydrochloric acid (HCl(aq)) yield aqueous aluminum chloride and hydrogen gas

6. calcium hydroxide + phosphoric acid (H3PO4(aq)) yield calcium phosphate + water

7. copper + sulfuric acid (H2SO4(aq)) produces copper(II) sulfate + water + sulfur dioxide

8. hydrogen gas + nitrogen monoxide gas form liquid water and nitrogen gas

Page 80Topic 2-12 Reaction Types 1:

Simple Combination and Simple Decomposition Reactions

A simple combination (SC) reaction is also known as a simple composition reaction or even a formation reaction.

In this type of reaction, a compound is formed from its individual elements, as in:

Sample Problem 1:Magnesium metal burns in oxygen in the air to produce magnesium oxide powder.Write a word equation and a balanced chemical equation for the process.

Word Equation:

Balanced Chemical Equation(Note: Write the chemical formulas for each chemical first, then balance the equation last.)

A simple decomposition (SD) reaction

is essentially the opposite of the sim

ple combination reaction which we hav

e just seen.

In a simple decomposition reaction, a compound breaks into its individual elements, as in:

Sample Problem 2:When aluminum thiosulfate powder is heated, it decomposes into its elements. Write a word equation and a balanced chemical equation for the process.

Word Equation

Balanced Chemical Equation(Again, remember to write the chemical formulas first and balance the equation last.)

Sample Problem 3Given the reactions below, first classify the reaction type as either simple combination (SC) or simple decomposition (SD); then balance the reaction.

(a) Type: ______ _____ N2O4(g) _____ N2(g) + _____ O2(g)

(b) Type: ______ _____ Fe(s) + _____ N2(g) _____ FeN(s)

Worksheet 2-12a Reaction Types 1:Simple Combination and Simple Decomposition Reactions

For each reaction given, first classify the reaction type as either simple combination (SC) or simple decomposition (SD). If necessary, write the chemical formulas of any missing chemicals. Lastly, balance the reaction.

Type

1. ______ Sulfur dioxide is produced by burning sulfur:

_____ S8(s) + _____ O2(g) _____ SO2(g)

2. ______ In 1774, Joseph Priestly discovered pure oxygen gas from the reaction:

_____ HgO(s) _____ Hg(l) + _____ O2(g)

3. ______ Molten table salt is industrially transformed into molten sodium.

_____ NaCl(l) _____ Na(l) + _____ Cl2(g)

4. ______ Nitrogen from the air reacts with hydrogen to produce ammonia for fertilizers.

_____ N2(g) + _____ H2(g) _____ NH3(g)

5. ______ Hydrogen is used as a rocket fuel to propel a satellite into space.

_____ H2(g) + _____ O2(g) _____ H2O(g)

6. ______ Copper ore (CuO(s)) is decomposed to remove the copper metal.

_____ CuO(s) _____ Cu(s) + _____ O2(g)

7. ______ Barbecue charcoal (C(s)) undergoes incomplete combustion to produce deadlycarbon monoxide gas.

_____ C(s) + _____ O2(g)

8. ______ Freshly cut lithium metal reacts with nitrogen from the air, producing lithiumnitride powder.

_____ + _____ _____ Li3N(s)

Topic 2-13 Reaction Types 2:Single and Double Replacement Reactions

Single Replacement (SR) ReactionsIn a single replacement (SR) reaction, an element reacts to replace another element within a reactant compound.

Sample Problem 1In the blank provided under each chemical, identify "element" and "compound" chemicals. Then, balance each single replacement reaction.

(a) _____ Zn(s) + ____ HF(aq) _____H2(g) + _____ ZnF2(aq)

______________ _____________ ____________ _____________

(b) _____ FeCl3(aq) + ____ I2(s) _____FeI3(aq) + _____ Cl2(g)

______________ _____________ __________ ___________

Double Replacement (DR) ReactionsIn a double replacement (DR) reaction, two ionic compounds react to form two new ionic compounds, as the "+" and "-" ions 'change partners'.Balance the double replacement reaction below.

_____ Na2S(aq) + ____ AgNO3(aq) _____Ag2S(s) + _____ NaNO3(aq)

Identify each reaction below as being either single replacement (SR) or double replacement (DR). Then, balance the reaction.

Type

(a) ___ K2CO3(aq) + ____ CaCl2(aq) ____KCl(aq) + ____ CaCO3(s)

(b) ___ Ni(NO3)2(aq) + ____ Li(s) ____Ni(s) + ____ LiNO3(aq)

(c) ___ Na(s) + ____ H2O(l) ____ NaOH(aq) + ____ H2(g)

Worksheet 2-13a Reaction Types 2:Single and Double Replacement Reactions

Identify each reaction below as being either single replacement (SR) or double replacement (DR).Then, balance the reaction.

Type

(a) ___ Na(s) + ____ HCl(aq) ____ NaCl(aq) + ____ H2(g)

(b) ___ Fe(NO3)3(aq) + ____ Mg(s) ____Fe(s) + ____ Mg(NO3)2(aq)

(c) ___ CsBr(aq) + ____ F2(g) ____ CsF(aq) + ____ Br2(l)

(d) ___ K2O(aq) + ____ CuCl2(aq) ____CuO(s) + ____ KCl(aq)

(e) ___ Li(s) + ____ H2O(l) ____ LiOH(aq) + ____ H2(g)

(f) ___ Sc(s) + ____ BeSO4(aq) ____ Sc2(SO4)3(aq) + ____ Be(s)

(g) ___ AgNO3(aq) + ____ NaCl(aq) ____ AgCl(s) + ____ NaNO3(aq)

(h) ___ K(s) + ____ GaF3(aq) ____Ga(s) + ____ KF(aq)

(i) ___ MgBr2(aq) + ____ F2(aq) ____MgF2(aq) + ____ Br2(l)

(j) ___ H2S(aq) + ____ Zn(aq) ____ZnS(s) + ____ H2(g)

(k) ___ Na3PO4(aq) + __ Ni(ClO4)2(aq) ____Ni3(PO4)2(s) + ____NaClO4(aq)

(l) ___ Ba(OH)2(aq) + ____ HBr(aq) ____BaBr2(aq) + ____ H2O(l)

(m) ___ H2SO4(aq) + ____ LiOH(aq) ____Li2SO4(aq) + ____ H2O(l)

Hydrocarbon and Carbohydrate Complete Combustion

Hydrocarbons contain two atoms only: _________________________

Carbohydrates contain three atoms: ___________________________

Hydrocarbons are common fuels:

C3H8(g): ________________________

C4H10(g): ________________________

C8H18(l): ________________________

C25H52(s): ________________________

"Combustion" means "burning". When hydrocarbons undergo complete combustion, there are only 2 compounds produced: CO2(g) and H2O(g).

STRATEGY: Balancing Hydrocarbon (CxHy) Complete Combustion ReactionsStep 1: Balance the C and H atoms first.

Step 2: Get the total oxygen atoms, for the right side of the equation.Two possible scenarios will occur now.

If this total oxygen atoms is an even number, then balance the O2(g) on the reactant side. Done.

orIf this total oxygen atoms is an odd number, then double up every balancing number except the O2(g), then balance the O2(g) last.

Sample ProblemEach reactant given undergoes complete hydrocarbon combustion. Write the chemical equation for the complete combustion and balance the equation.

(a) C5H12(l)

(b) C4H10(g)

Practice ProblemsBalance each complete combustion reaction.

(a) _____ C6H12(g) + _____ O2(g) _____ CO2(g) + _____ H2O(g)

(b) _____ C6H14(g) + _____ O2(g) _____ CO2(g) + _____ H2O(g)

(c) _____ C6H12O6(s) + _____ O2(g) _____ CO2(g) + _____ H2O(g)

(d) _____ C7H16(g) + _____ O2(g) _____ CO2(g) + _____ H2O(g)

(e) _____ C2H6(g) + _____ O2(g) _____ CO2(g) + _____ H2O(g)

The Five Main Reaction Types

Classify each reaction as one of the five main reaction types: simple combination (sc), simple decomposition (sd), single replacement (sr), double replacement (dr), or complete hydrocarbon combustion (hc) in the blank to the left of the question number. If a reaction does not fit any of these types, then classify it as "other" (o). Then, balance the chemical reaction.

Type

1. ___ Cu(s) + ____ O2(g) ____ CuO(s)

2. ___ H2O(l) ____ H2(g) + ____ O2(g)

3. ___ Fe(s) + ___ H2O(l) ____ H2(g) + ____ Fe3O4(s)

4. ___ AsCl3(aq) + ___ H2S(aq) ____ As2S3(s) + _____HCl(aq)

5. ___ CuSO4(s) ____ Cu(s) + ____ S8(s) + ____ O2(g)

6. ___ Fe2O3(s) + ___ H2(g) ____ Fe(s) + ____ H2O(l)

7. ___ CaCO3(s) ____ CaO(s) + ____ CO2(g)

8. ___ Fe(s) + ___ S8(s) ____ FeS(s)

9. ___ H2S(s) + ___ KOH(aq) ____ HOH(l) + ____ K2S(aq)

10. ___ NaCl(s) ____ Na(s) + ____ Cl2(g)

11. ___ Al(s) + ___ H2SO4(aq) ____ H2(g) + _____Al2(SO4)3(aq)

12. ___ H3PO4(aq) + ___ NH4OH(aq) ____ HOH(l) + ____ (NH4)3PO4(aq)

13. ____ C3H8(g) + _____ O2(g) _____ CO2(g) + _____ H2O(g)

14. ___ Al(s) + ___ O2(g) ____ Al2O3(s)

15. ____ CH4(g) + _____ O2(g) _____ CO2(g) + _____ H2O(g).