Page 167 - Theory and Problems of BEGINNING CHEMISTRY

156 STOICHIOMETRY [CHAP. 10

Ans. (a) 2 Na + Cl 2 −→ 2 NaCl

1 mol Cl 2
1.22 mol Na = 0.610 mol Cl 2 reacts
2 mol Na
(b) We calculated in part (a) that 0.610 mol of Cl 2 is needed to react. As long as we have at least
0.610 mol present, 0.610 mol Cl 2 will react.
(c) Since we have more Cl 2 than that, the Na is in limiting quantity.

10.38. What mass of CO 2 can be produced by the complete combustion of 2.00 kg of octane, C 8 H 18 , a major
component of gasoline, in 8.00 kg of oxygen?

Ans. 2C 8 H 18 + 25 O 2 −→ 16 CO 2 + 18 H 2 O

1000 g 1 mol C 8 H 18
2.00 kg C 8 H 18 = 17.5 mol C 8 H 18 present
1kg
114gC H 18
8
1000 g 1 mol O 2

8.00 kg O 2 = 250 mol O 2 present
1kg 32.0gO 2

25 mol O 2
17.5 mol C 8 H 18 = 219 mol O 2 required
2 mol C 8 H 18
Since 219 mol of O 2 is required and 250 mol O 2 is present, C 8 H 18 is in limiting quantity.

16 mol CO 2 44.0gCO 2
17.5 mol C 8 H 18 = 6160 g = 6.16 kg CO produced
2
2 mol C 8 H 18 1 mol CO 2
10.39. If you were treating two chemicals, one very cheap and one expensive, to produce a product, which
chemical would you use in excess, if one had to be in excess?
Ans. Economically, it would be advisable to use the cheap one in excess, since more product could be obtained
per dollar by using up all the expensive reactant.
CALCULATIONS BASED ON NET IONIC EQUATIONS
10.40. What mass of each of the following silver salts would be required to react completely with a solution
containing 35.5 g of chloride ion to form (insoluble) silver chloride? (a) AgNO 3 ,(b)Ag 2 SO 4 , and
(c) AgC 2 H 3 O 2 .
1 mol Cl − 1 mol Ag +

Ans. 35.5gCl − = 1.00 mol Ag +
35.5gCl − 1 mol Cl −
1 mol AgNO 169.9 g AgNO

(a)1.00 mol Ag + 3 3 = 170 g AgNO
1 mol Ag + 1 mol AgNO 3 3

1 mol Ag SO 4 311.8gAg SO 4
2
2
(b) 1.00 mol Ag + = 156 Ag SO 4
2
2 mol Ag + 1 mol Ag SO 4
2

1 mol AgC H 3 O 2 166.9 g AgC H 3 O 2
2
2
(c) 1.00 mol Ag + = 167 g AgC H 3 O 2
2
1 mol Ag + 1 mol AgC H 3 O 2
2
HEAT CAPACITY AND HEAT OF REACTION
10.41. The student political science society decides to take a trip to Washington, D.C. The hostel rate is $20 per
student each night. How much will it cost for 23 students to stay for three nights?
20 dollars
Ans. 23 students 3 nights = 1380 dollars
student · night
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10.42. A system is initially at 15 C. What will be the final temperature if the system (a) is warmed 35 C and
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(b) is warmed to 35 C? (c) What is the difference between final temperature and temperature change?
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Ans. (a)50 C (b)35 C (c) The temperature difference is the final temperature minus the initial temperature.
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The final temperature is merely a single temperature. Be sure to read the problems carefully so that you do
not mistake temperature change for initial or final temperature.