UNIT 3 SELF-QUIZ
(Page 412)
1. False: A physical change usually involves a larger enthalpy change than does a chemical change.
2. True
3. False: The potential energy of the products is smaller than the potential energy of the reactants in an exothermic change. 4. True
5. False: An endothermic reaction absorbs heat from the surroundings.
6. True
7. True
8. False: Three-quarters of a radioisotope will have changed after two half-lives.
9. False: In an endothermic reaction, only the potential energy of the chemical system increases.
10. True
11. (b)
12. (c)
13. (e)
14. (a)
15. (e)
16. (c)
17. (b)
18. (d)
19. (b)
20. (e)
21. (b)
22. (a)
23. (c)
24. (c)
25. (e)
26. (c)
27. (b)
28. (d)
29. (c)
30. (d)

UNIT 3 REVIEW
(Page 414)

Understanding Concepts
1. qwater = mc∆T
= 1500 g ϫ 4.18 J/(g•ºC) ϫ (75 – 20)ºC qwater = 340 kJ
2. MCl = 70.9 g/mol
2
1 mol nCl = 2250 g ϫ ᎏᎏ
2
70.9 g nCl = 31.7 mol
2

∆H = nCl ∆Hvap
2

= 31.7 mol ϫ 20.7 kJ/mol
∆H = 657 kJ

218

Unit 3

Copyright © 2003 Nelson

3. (a) qwater = mc∆T
= 100.0 g ϫ 4.18 J/(g•ºC) ϫ 5.6ºC qwater = 2341 J nNaOH = MV
= 0.700 mol/L ϫ 0.600 L nNaOH = 0.420 mol

n∆Hneut = qwater qwater ∆Hneut = ᎏᎏ n 2341 J
= ᎏᎏ
0.420 mol
∆Hneut = 5573 J/mol, or 5.57 kJ/mol
Because the reaction is exothermic, ∆Hneut = –5.57 kJ/mol.
(b) The assumption is that the reaction went to completion and that all heat from the reaction was absorbed by the water in the calorimeter and not by the calorimeter or surroundings.
3
4. (a) 2 C(s) + ᎏᎏ H2(g) + 1/2 Cl2(g) + 37.3 kJ → C2H3Cl(g)
2
3
(b) 2 C(s) + ᎏᎏ H2(g) + 1/2 Cl2(g) → C2H3Cl(g)
∆H = +37.3 kJ
2
5. (a) S(s) + O2(g) → SO2(g)
∆H = –296.8 kJ
(b)

Potential Energy Diagram of the
Formation of Sulfur Dioxide

enthalpy of
S(g) + O2(g)

Ep

∆H = –296.8 kJ enthalpy of SO2(g)

Reaction Progress

(c) MSO =