1. Chemistry B11
Chapter 5
Chemical Reactions

2. Chemical Reactions
Chemical transformation or change = Chemical reaction
Substance(s) is used up (disappear / re-arrange)
New substance(s) is formed.
Different physical and chemical properties.

3. Chemical Reactions

4. A + B  AB or C + D Chemical Reactions Reactants Product or Products
Elements are not
created nor destroyed
Chemical Equation

5. Chemical Reactions 1. A + B  AB 2. AB  A + B 3. A + BC  AC + B 4.
Synthesis reaction (combination)
2H2 + O2  2H2O
AB  A + B 2.
Decomposition
2NaCl  2Na + Cl2
A + BC  AC + B 3.
Single replacement reaction
Fe + CuSO4  FeSO4 + Cu
AB + CD  AD + CB 4.
Double replacement reaction
NaCl + AgNO3  NaNO3 + AgCl

6. Physical state irrelevant
Chemical Reactions 5.
AB + xO2  yCO2 + zH2O
Combustion
“Burning”
C3H8 + 5O2  3CO2 + 4H2O
Physical state irrelevant
Solid (s)
Liquid (l)
Gas (g)
Aqueous (aq)
Ca(OH)2(s) + 2HCl(g)  CaCl2(s) + H2O(l)

7. Chemical reactions and heat
Chemical reactions speed up
With increased heat
This is due to several reasons:
Activation energy
Increased energy
Quicker motion more interactions

8. Balance a chemical equation
Why balancing?

9. Balance a chemical equation
Law of conservation of mass
Atoms are neither destroyed nor created.
They shift from one substance to another.
“Fruit Salad”

10. Balance a chemical equation
Begin with atoms that appear in only one compound on the left and right.
If an atom occurs as a free element, balance it last.
Change only coefficients (not formulas).
C3H8(g) + O2(g)  CO2(g) + H2O(g)
begin
last

11. Formula and Molecule Formula Weight of NaCl:
Ionic & covalent compounds  Formula formula of NaCl
Covalent compounds  Molecule molecule of H2O
Formula Weight of NaCl:
23 amu Na amu Cl = 58.5 amu NaCl
Molecular Weight of H2O:
2 (1 amu H) + 16 amu O = 18 amu H2O

12. Mole Mole (mol): formula weight of a substance (in gram).
12g of C = 1 mol C
23g of Na = 1 mol Na
58.5 g of NaCl = 1 mol NaCl
18 g of H2O = 1 mol of H2O

13. Avogadro’s number (6.02×1023): number of formula units in one mole.
1 mole of apples = 6.02×1023 apples
1 mole of A atoms = 6.02×1023 atoms of A
1 mole of A molecules = 6.02×1023 molecules of A
1 mole of A ions = 6.02×1023 ions of A
Molar mass (g/mol): mass of 1 mole of substance (in gram)
(Formula weight)
molar mass of Na = 23 g/mol
molar mass of H2O = 18 g/mol

14. 2H2O(l)  2H2(g) + O2(g) Stoichiometry 2 2 1 2 moles 2 moles 1 mole
Relationships between amounts of substances in a chemical reaction.
Look at the Coefficients!
2H2O(l)  2H2(g) + O2(g) 2 2 1
2 moles
2 moles
1 mole
2 liters
2 liters
1 liter
2 particles
2 particles
1 particle
2 grams
1 gram

15. 1 step: use coefficient in the balanced equation.
mole B
mass
volume
Particle
(atom)
(molecule)
(ion)
1 step: use coefficient in the balanced equation.
CH4 + 2O2  CO2 + 2H2O

16. STP: 1 mole of substance (gas) = 22.4 L = 22400 cc (cm3 or mL)
CH4 + 2O2  CO2 + 2H2O
2 moles H2O
23 mole CH4 = ? moles H2O
23 mole CH4 (
) = 46 moles H2O
1 mole CH4
10 cc O2 = ? cc CO2
10 cc O2 (
1 cc CO2
2 cc O2
) = 5 cc CO2
32 g CH4 = ? moles CO2
32 g CH4 (
1 mole CH4
16 g CH4
) = 2 mole CO2
1 mole CO2 )(
40 g CH4 = ? L CH4
40 g CH4 (
1 mole CH4
16 g CH4
) = 56 L CH4
22.4 L CH4 )(
STP: 1 mole of substance (gas) = 22.4 L = cc (cm3 or mL)

17. Limiting Reagents N2(g) + O2(g)  2NO(g) Stoichiometry: 1 mole 1 mole
2 moles
Before reaction:
1 mole
4 moles
After reaction:
0 mole
3 moles
2 moles

18. Limiting Reagents N2(g) + O2(g)  2NO(g) Stoichiometry: 1 mole 1 mole
2 moles
Before reaction:
1 mole
4 moles
Left over
After reaction:
0 mole
3 moles
2 moles
Used up first

19. Limiting Reagents N2(g) + O2(g)  2NO(g) Limiting reagent
Stoichiometry:
1 mole
1 mole
2 moles
Before reaction:
1 mole
4 moles
Left over
After reaction:
0 mole
3 moles
2 moles
Used up first

20. Limiting Reagents N2(g) + O2(g)  2NO(g)
Limiting reagent: is the reactant that is used up first.
Limiting reagents can control a reaction:
N2(g) + O2(g)  2NO(g)

21. Limiting Reagents C(s) + O2(g)  CO2(g) Example:
12g of C
64g of O2
? Limiting reagent
? g of CO2 will be formed
Make sure that the chemical equation is balanced.
C(s) + O2(g)  CO2(g)
1 mol
12g C (
1 mole C
12g C
) = 1 mole C
64g O2 (
1 mole O2
32g O2
) = 2 mole O2
C is the limiting reagent.

22. Limiting Reagents A B C(s) + O2(g)  CO2(g) ? g of CO2 will be formed:
We should use the mass of the limiting reagent.
(because it controls our reaction).
12g C (
1 mole C
12g C )(
1 mole CO2
44g CO2
) = 44g CO2

23. Percent Yield actual yield Percent yield = × 100 theoretical yield
actual yield: mass of product formed (experimental)
theoretical yield: mass of product that should form
(according to stoichiometry)
N2(g) + O2(g)  2NO(g)
theoretical yield = 40g NO
actual yield = 37g NO
Percent yield =
37g NO
40g NO
× 100 = 92.5%
7.5% error or lost

24. Aqueous Solution (ionic compounds)
H2O
NaCl(s) Na+(aq) + Cl-(aq)
Dissociation (Ionization)
aqueous solution: solvent is water
AgNO3(s) Ag+(aq) + NO3-(aq)
H2O
NaCl
AgNO3
NaCl(aq) + AgNO3(aq)  AgCl(s) + NaNO3(aq)

25. total charge on left side = total charge on right side
Molecular equation:
NaCl(aq) + AgNO3(aq)  AgCl(s) + NaNO3(aq)
Ionic equation:
Na+(aq) + Ag+(aq) + Cl-(aq) + NO3-(aq)  AgCl(s) + Na+(aq) + NO3-(aq)
Net ionic equation:
Na+(aq) + Ag+(aq) + Cl-(aq) + NO3-(aq)  AgCl(s) + Na+(aq) + NO3-(aq)
Spectator ions
Ag+(aq) + Cl-(aq)  AgCl(s)
2As3+(aq) + 3s2-(aq)  As2S3(s)
total charge on left side = total charge on right side

26. oxidation: is the loss of electrons.
Oxidation and Reduction reactions (redox)
oxidation: is the loss of electrons.
reduction: is the gain of electrons.
Zn(s) + Cu2+(aq)  Zn2+(aq) + Cu(s)
redox reaction
Zn(s)  Zn2+(aq) + 2e- Zn is oxidized (reducing agent)
Cu2+(aq) + 2e-  Cu(s) Cu2+ is reduced (oxidizing agent)

27. double replacement reactions  non redox
Oxidation and Reduction reactions (redox)
oxidation: is the gain of oxygen / loss of hydrogen.
reduction: is the loss of oxygen / gain of hydrogen.
CH4(s) + 2O2(g)  CO2(g) + 2H2O(g)
redox reaction
C gains O and loses H
is oxidized
(reducing agent)
O gains H
Is reduced
(oxidizing agent)
single replacement reactions and combustion reactions  redox reactions
double replacement reactions  non redox

28. 2HgO(s) + heat (energy)  2Hg(l) + O2(g)
Heat of reaction
2HgO(s) + heat (energy)  2Hg(l) + O2(g)
Endothermic reaction
C3H8(s) + 5O2(g)  3CO2 + 4H2O + heat (energy)
Exothermic reaction
All combustion reactions are exothermic.