HOMEWORK for UNIT 4. Reactions
Balancing equations (text section 11.1)
1. Using this chemical equation, 2 NO (g) + O
2
(g)

2 NO
2
(g) a. explain the difference between a subscript and a coefficient and give an example. b. Draw a circle picture to illustrate the molecules in this balanced chemical equation.
2. Balance each equation in lowest terms & list the coefficients. a. Cr
2
O
3
(s) + C (s)

Cr (s) + CO (g) b. Na (s) + H
2
O (l)

NaOH (aq) + H
2
(g) c. C
5
H
12
(l) + O
2
(g)

CO
2 d. NH
3
(g) + O
2
(g)

(g) + H
2
O (g)
NO (g) + H e. Ag (s) + H
2
S (g) + O
2
(g

Ag
2
O (g)
2
S (s) + H
2
O (l) f. AgNO
3
(aq) + Cu (s)

Cu(NO
3
)
2
(aq) + Ag (s) g. C
2
H
5
OH (l) + O
2
(g)

CO
2
(g) + H
2
O (g) h. FeS
2
(s) + O
2
(g)

SO
2
(g) + Fe
2
O
3
(s)
Stoichiometry (text pg 359–362)
3. What is the mole ratio of O
2
to NO in this balanced chemical equation? Include units.
4 NH
3
(g) + 5 O
2
(g)

4 NO (g) + 6 H
2
O (l)
4. How many moles of oxygen gas are needed to react with 0.875 moles of NH
3
?
4 NH
3
(g) + 5 O
2
(g)

4 NO (g) + 6 H
2
O (l)
5. How many grams of water form when 0 .
18 moles of NH
3
form?
2 NO
2
(g) + 7 H
2
(g)

2 NH
3
(g) + 4 H
2
O (l)
6. How many moles of CO gas are needed to react with 10.0 g of Fe
2
O
3
?
Fe
2
O
3
(s) + 3 CO (g)

2 Fe (l) + 3 CO
2
(g)
7. How many grams of carbon dioxide gas form when 703 g C
8
H
18
(one liter of octane) burns?
2 C
8
H
18
(l) + 25 O
2
(g)

16 CO
2
(g) + 18 H
2
O (g)
8. How many grams of NaHCO
3
(baking soda) are needed to produce 4.40 g carbon dioxide gas by this reaction?
H
2
SO
4
(aq) + 2 NaHCO
3
(s)

2 H
2
O (l) + 2 CO
2
(g) + Na
2
SO
4
(aq)
9. How grams of hydrogen gas are produced when 1.2 g of Al react in this reaction?
2 Al (s) + 6 HCl (aq)

2 AlCl
3
(aq) + 3 H
2
(g)
Thermochemical equations and stoichiometry
10. Identify each reaction as exothermic or endothermic. a. C
3
H
6
O (l) + 4 O
2
(g)

3 CO
2
(g) + 3 H
2
O (l) + 1790 kJ b. 178 kJ + CaCO
3
(s)

CaO (s) + CO
2
(g) c. 41.2 kJ + CO
2
(g) + H
2
(g)

CO (g) + H
2
O (g) d. 2 SO
2
(g) + O
2
(g)

2 SO
3
(g) + 197.8 kJ
11. How much energy is released when 283 g Ca(OH)
2
are produced in this reaction:

CaO (s) + H
2
O (l)

Ca(OH)
2
(s) + 65.2 kJ
12. How many grams of SO
2
can be produced if 125 kJ of energy are available to do this reaction:
197.8 kJ + 2 SO
3
(g)

2 SO
2
(g) + O
2
(g)
13. How much energy is needed to produce 7.50 g NO in this reaction:
181 kJ + N
2
(g) + O
2
(g)

2 NO (g)
14. How many grams of Al must react to produce 275 kJ in this reaction:
Fe
2
O
3
(s) + 2 Al

Al
2
O
3
(s) + 2 Fe (s) + 852 kJ
ANSWERS to stoichiometry problems
4. 1.09 mol O
2
5. 6.5 g H
2
O
6. 0.188 mol CO
7. 2.17x10
3
g CO
2
8. 8.40 g NaHCO
3
9. 0.13 g H
2
11. 249 kJ
12. 81.0 g SO
2
13. 22.6 kJ
14. 17.4 g Al

Extra stuff
Reaction types (text section 11.2)
3. Write balanced chemical equations for the following reactions
[Hint: hydrogen, nitrogen, oxygen, and all halogens are diatomic elements, so hydrogen is H
2
, not H]:
(pp 330-336) a. The synthesis of aluminum chloride (AlCl
3
) from its elements. b. The combustion of propane gas (C
3
H
8
). c. Ammonium nitrate (NH
4
NO
3
) decomposes to nitrogen, oxygen, and water. b. Nitrogen and oxygen combine to form dinitrogen pentoxide. d. Sodium hydrogen carbonate (NaHCO
3
) decomposes to sodium oxide, carbon dioxide, and water. e. The combustion of butanol (C
4
H
9
OH)
4. Complete and balance these single replacement reactions. a. Zn (s) + CuCl
2
(aq)
 b. Br
2
(aq) + KI (aq)
 c. Mg (s) + HCl (aq)

(pp 330-336)
5. Complete and balance these double replacement precipitation reactions. a. AgNO
3
(aq) + NaCl (aq)
 b. BaCl
2
(aq) + K
2
CO
3
(aq)
 c. Sr(NO
3
)
2
(aq) + Na
2
SO
4
(aq)

(pp 330-336)
6. Identify each reaction by type: synthesis (S), decomposition (D), combustion (C), single replacement
(SR), or double replacement–pptn (DR). The reactions are already balanced. a. Fe (s) + CuSO
4
(aq) b. 2 H
2
O
2
(aq)

2 H
2

FeSO
O (l) + O
4
2
(aq) + Cu (s)
(g) c. Br
2
(aq) + 2 KI (aq)

2 KBr (aq) + I
2
(aq) d. 2 Ba (s) + O
2
(g)

2 BaO (s) e. Ba(NO
3
)
2
(aq) + K
2
SO
4
(aq)

BaSO
4
(s) + 2 KNO
3
(aq) f. 2 C
4
H
10
(l) + 13 O
2
(g)

8 CO
2
+ 10 H
2
O (l)
(pp 330-336)

HOMEWORK for UNIT 4. Reactions
Answers a. 0.0207 mol b. 0.128 g c. 58.0 g d. 0.378 g
14. Balance each chemical equation, identify the type of reaction, and solve the stoichiometry problem: a. How many moles of KCl form when 2.16 g BaCl
2
react?
BaCl
2
+ K
2
SO
4

BaSO
4
+ KCl b. How many grams of H
2
are produced when 0.127 mol HCl react?
Zn + HCl

ZnCl
2
+ H
2 c. How many grams of CO
2
form when 26.4 g C
3
H
7
OH react?
C
3
H
7
OH + O
2

CO
2
+ H
2
O d. How many grams of KClO
3
are needed to produce 0.148 g O
2
?
KClO
3

KCl + O
2

HOMEWORK for UNIT 4. Reactions
Answers 15a. 5.66 g 15b. 85.0 g 17a. 34 kJ 17b. 5.23 kJ
15. Balance each chemical equation, identify the type of reaction, and solve the stoichiometry problem: a. How many grams of Ag
2
CrO
4
form when 0.0341 mol AgNO
3
react?
AgNO
3
(aq) + K
2
CrO
4
(aq)

Ag
2
CrO
4
(s) + KNO
3 b. How many grams of CO
2
are produced when 35.8 g (C
2
H
5
)
2
O react?
(C
2
H
5
)
2
O + O
2

CO
2
+ H
2
O
16. Describe the difference between heat and temperature. Include an example.
17. Use the relationship q = mc∆T and c water
= 4.184 J/g °C to solve these problems: a. Calculate the energy needed, in kJ, to heat 245 g water from 4 °C to 37 °C. b. If 50 .
0 g of water at 30 .
0 °C cool to 5
.
0 °C, how many kilojoules of energy did the water lose?

HOMEWORK for UNIT 4. Reactions
Answers 18b. –1.4 x 10
3
kJ/mol 19a. 24 kJ/mol 20b. 23.4 x 10
3
kJ 20c. 1390 g CO
2
Useful information: q = mc∆T and c water
= 4.184 J/g °C
18. A student finds that when 0 .
65 g of ethanol (C
2
H
5
OH) burns, the temperature of 235 g of water increases from 18 .
2 °C to 37 .
8 °C. The reaction is C
2
H
5
OH (l) + O
2
(g)

CO
2
(g) + H
2
O (l) a. Balance the chemical equation. b. Calculate the heat of combustion of ethanol, in kJ per mole C
2
H
5
OH. c. Draw a simple enthalpy diagram to illustrate the enthalpy change in this reaction. Is the reaction exothermic or endothermic?
19. A student adds 13 .
7 g potassium iodide to 100 .
0 g water initially at 18 .
4 °C. As the salt dissolves, the temperature decreases to 14 .
9 °C. The reaction is KI (s)

KI (aq) a. Calculate the heat of solution of potassium iodide, in kJ per mole KI, using the same assumptions you used in your lab. b. Put the energy into the balanced equation. c. Draw a simple diagram to illustrate the enthalpy change in this reaction. Is the reaction exothermic or endothermic?
20. Propane, C
3
H
8
, is the fuel used in gas barbeques. ∆H for the combustion of propane is –2220 kJ/mol. a. Balance the equation for the combustion reaction and put the energy into the equation:
C
3
H
8
(l) + O
2
(g)

CO
2
(g) + H
2
O (l)
Is the reaction exothermic or endothermic? b. The propane canister for a small portable barbeque contains 465 g C
3
H
8
. How many kJ of heat energy are produced when all of the propane in the canister burns? c. How many grams of CO
2
are produced when all the propane in the canister burns?

9. A student adds 1.82 g Zn to 100.0 mL of dilute HCl solution at 20.3 °C. As the Zn reacts with the
HCl, the temperature rises to 30.5 °C. The reaction is Zn (s) + 2 HCl (aq) 
ZnCl
2
(aq) + H
2
(g) a. Calculate the heat of reaction, in kJ per mole of Zn [hint: assume the density of the HCl solution is
1.00 g/mL, and use c = 4.184 J/g °C; the Zn dissolves, so add its mass to the HCl solution mass] b. Draw a simple enthalpy diagram to illustrate the enthalpy change in this reaction. Is the reaction exothermic or endothermic?