Chapter 8

Balancing Chemical Equations

8.1 Chemical Equations

Chemical equations represent, with symbols and formulas, the reactants and products in a chemical reaction. reactants products

Requirements for all chemical equations: must show all reactants and products formulas must be correct Law of Conservation of Mass must be satisfied (equation

must be balanced)

Chemical Equations

Balanced Equations – use coefficients H2 + Cl2 2 HCl

Hydrogen reacts with chlorine to yield hydrochloric acid

Symbols used in equations 2NaCl(s) 2Na(s) + Cl2(g)

NaCl(aq) - solution of sodium chloride in water

H2O(l) – liquid water

g or ↑ = gas

Chemical Equations

More symbols = one way reactions ↔ = reversible reaction ΔH = heat cat = catalyst (a substance that speeds up a

reaction without being used up in the reaction) S or ppt or ↓ = precipitate (solid - only found on

products side)

Chemical Equations

Significance of chemical equations H2(g) + Cl2(g) 2 HCl (g) means…

Atoms: 2 atoms of hydrogen gas react with 2 atoms of chlorine gas and yields 2 atoms of hydrogen, 2 atoms of chlorine

Molecules: 1 molecule of hydrogen gas reacts with 1 molecule of chlorine gas and yields 2 molecules of hydrochloric acid

Molar mass: H = 2.0; Cl = 71.0; HCl = 73.0

Balancing Chemical Equations

Helpful hints to balancing…. 1 atom at a time Balance atoms that appear only 1X per side first Balance polyatomic ions as whole units Balance diatomic elements last Save H + O for last

Balancing Chemical Equations

Examples __H2O(l) __ H2(g) +__O2(g)

__(NH4)2CO3 (aq)+__CaCl2(s) __CaCO3(s) +__NH4Cl(aq)

Balancing Chemical Reactions

__Al(s) + __Br2(g) __AlBr3(s)

__C2H5OH(g) + __O2(g) __CO2(g) +__H2O(l)

NOT IN PACKET!!

_C3H6 + _ O2 _ CO2 + _H2O

Balancing Chemical Reactions

Balancing Chemical Equations

Tin (IV) oxide + Carbon Tin + Carbon monoxide

SnO2(aq) + C(s) Sn(s) + CO(g)

SnO2(aq) + 2C(s) Sn(s) + 2CO(g)

Balancing Chemical Equations

Aqueous Iron (III) Chlorate reacts with solid calcium to yield calcium chlorate and solid iron

Fe(ClO3)3(aq) + Ca (s) Ca(ClO3)2(aq) + Fe(s)

2Fe(ClO3)3(aq) + 3Ca (s) 3Ca(ClO3)2(aq) + 2Fe(s)

8.2 Types of Chemical Reactions

5 types synthesis decomposition combustion single replacement double replacement

Remember: You must first find the correct products, then balance the equation!

Types of Chemical Reactions

Synthesis (direct combination) - needs

energy to happen (usually heat) General formula

A + B ---> AB

2H2 + O2 → 2H2O

Types of Chemical Reactions

Synthesis Examples Ba + S

Mg + Cl2

Al + Cl2

Na + O2

REMEMBER TO BALANCE!!!!!!!!!!

BaS

MgCl2

AlCl3

Na2O

Types of Chemical Reactions

Decomposition (analysis) - needs energy to happen (usually heat or electricity) general formula

AB ---> A + B

2H2O → 2H2 + O2

Types of Chemical Reactions

Examples FeCl3

HgO

CuSO4 · 5 H2O

Fe + Cl2

Hg + O2

CuSO4(s) + H2O(g)

Types of Chemical Reactions

Combustion - the reaction of hydrocarbons and oxygen General Formula

CxH y + O2 CO2 + H2O

Types of Chemical Reactions

CH4 + O2 → CO2 + H2O

C3H8 + O2 → CO2 + H2O

C4H10 + O2 → CO2 + H2O

C2H5OH + O2 → CO2 + H2O

Types of Chemical Reactions

Single replacement - take place in aqueous

solutions - need very little energy to happen Two Types

Positive Ions Switch AB + M MB + A

Negative Ions Switch MB + X MX + B

Types of Chemical Reactions

Positive Ions Switch HI(aq) + Mg(s)

AlCl3(aq) + Ca(s)

Ca(s) + HOH(l)

MgI2(aq) + I2(s)

CaCl2(aq) + Al(s)

Ca(OH)2(aq) + H2(g)

Types of Chemical Reactions

Negative Ions Switch NaCl + F2

BaS + O2

NaF + Cl2

BaO + S

Types of Chemical Reactions

Double Replacement - aqueous solution - little energy - usually forms one soluble ionic product (aka - aqueous) and either a ppt, water, or a

gas that bubbles out of water General Formula (molecule + molecule)

AB + CD CB +AD

AgNO3 + NaCl → AgCl + NaNO3

Types of Chemical Reactions

FeCl3 + NaOH

H2SO4 + NaOH

NH4Cl + NaOH

Fe(OH)3 + NaCl

HOH + Na2SO4

NH4OH + NaCl

8.3 Activity Series of the Elements

Another Lie!! : ) Some reactions happen and some don’t!

Assume all synthesis, decomposition, and combustions happen

Not all single or double displacement occur Single Replacement

Use activity series Double Replacement

Use solubility table

Activity Series of the Elements

Rules for the single replacement activity series: Any single element above an element in a

compound will replace it. The top 5 elements react with water. Metals above H react with acids (molecules

that start with H – not water). The nonmetal reactivity series is F> Cl >

Br...

Activity Series of the Elements

Ca + H2O →

Al + H2O →

Al + HI →

Ca(OH)2 + H2

No Rxn

AlI3 + H2

Activity Series of the Elements

Cu + HI

NaCl + F2

NaF + Cl2 →

No Rxn

NaF + Cl2

No Rxn

Solubility Table of the Elements

Rules for double replacement reactions using a solubility table: If one of the products formed is water, the

reaction happens. If a gas is formed, the reaction happens. If an insoluble product forms (I or Ss), the

reaction happens

Solubility Table of the Elements

Na2CrO4 + KCl →

FeCl3 + KOH →

HCl + NaOH →

No Rxn

Fe(OH)3(ppt) + KCl(aq)

H2O(l) + NaCl(s)

Solubility Trends

Cations very soluble - Na, K, ammonium very insoluble- Ag, Pb, Hg, transitions

Anions - very soluble – nitrate for monatomics- F>Cl>Br .... very insoluble - carbonate, hydroxide, phosphate, sulfate sulfides - decompose

General trend - As size decreases, solubility increases OR Heavier stuff doesn’t dissolve well

Showing Energy Changes in Equations

endothermic - A + B + heat

C ΔH is positive

exothermic - A + B C + heat

ΔH is negative

Some helpful notes on writing phases in chemical reactions

Metals are solids (except Hg, Br) SR and DR reactions, reactants that are compounds are

always aqueous. SR and DR reactions, products that are compounds

should have their phases identified using a solubility chart (aqueous vs. precipitate)

S and D reactions, ionic compounds are solids. In C reactions, the water, CO2, and O2 are gases. The

hydrocarbon is hard to tell, but is usually a liquid after C=6 or higher.

Most other covalent compounds are gases. Acids (chemicals starting with hydrogen) are always

aqueous