Chemistry

Answers to Chapter 10 Study Questions

 

1. a) reactants

20

H = -20 kJ products

0

b) exothermic

c) Reactants have greater heat content.

d) Heat is released.

 

2. a) exothermic b) exothermic c) endothermic

d) exothermic e) exothermic f) endothermic

 

3. a) C10H8(s) + 12 O2(g) 10 CO2(g) + 4 H2O(l) H = - 5159 kJ

b) exothermic

c)

d)

 

4. (i) Pb(s) + 0.5 O2(g) PbO(s) H = -217.9 kJ

(ii) 3 Pb(s) + 2 O2(g) Pb3O4(s) H = -734.7 kJ; therefore:

2 x (ii) = 6 Pb(s) + 4 O2(g) 2 Pb3O4(s) H = 2(-734.7) = -1469 kJ

-6 x (i) = 6 PbO(s) 6 Pb(s) + 3 O2(g) H = -6(-217.9) = +1307 kJ

overall reaction = 6 PbO(s) + O2(g) 2 Pb3O4(s) H = -1469 + 1307 = -162 kJ

Exothermic

 

5. Q (J) = specific heat (J/g C) x mass (g) x T (C); T = 90.0 - 25.0 = 65.0C

392 J = specific heat x 48.0 g x 65.0C

 

6. a) T = 19.23 - 24.78 = -5.55 C

b) Water got colder, so heat was used up and the process is endothermic.

c) Q (J) = specific heat (J/g C) x mass (g) x T (C)

Q = 4.18 J/g C x 60.0 g x -5.55 C = -1390 J = 1390 J (used up)

d) molar mass (NH4Cl) = 14.0 + 4.0 + 35.5 = 53.5 g/mole

e)