Chemistry - A Molecular Science

9.14

EXERCISES 1.

What are the signs of

HΔ

o and

SΔ

o for the evaporation of water?

2. What are the signs of

HΔ

o and

SΔ

o for cooling liquid water?

3. A system gives off 600 J of heat while 200 J of work are done on it. What

are

E, Δ

EΔ

sur

, and

EΔ

univ

?

4. A system does 400 J of work and absorbs 150 J of heat. What are

E, Δ

EΔ

(^) sur
and
EΔ
univ
?

5. What is the difference between

H and Δ

E? Why is Δ

H used more Δ

frequently by chemists than

E? Δ

6. What are the standard states of a gas and a solute? 7. When is the entropy change of a

reaction expected to be significant?

8.

Indicate whether each of the following

is true, false, or cannot be

determined for a non-extensive reaction at constant pressure and temperature that is proceeding spon

taneously to consume gas molecules.

a)

G < 0 Δ

b)

SΔ

o ~ 0

c)

GΔ

o < 0

d)

EΔ

univ

= 0

e)

HΔ

o < 0

f) the extent of reaction increases with T

9.

Indicate whether each of the following

is true, false, or cannot be

determined for an extensive endothermic reaction that is at equilibrium at constant pressure and temperature.

a)

G < 0 Δ

b)

HΔ

o < 0

c)

GΔ

o < 0

d)

SΔ

univ

> 0

e)

SΔ

o > 0

f) the extent of reaction increases with T

10.

The enthalpy of combustion of propane gas, C

H 3

(g), is -2,220 kJ/mol. 8

a) Write the balanced equation for the combustion reaction. b) Propane is often used for gas grills, which usually have a propane tank

with 20 pounds of propane. How much heat can be obtained by burning all of the propane in a 20 lb tank? (1 lb = 454 g)

c) What is the enthalpy change for 6CO

(g) + 8H 2

O(l) 2

→

2C

H 3

(g) + 8

10O

(g)? 2

11.

Combustion of 0.150 g of C

H 2

OH(l) (grain alcohol) 5

releases 4.47 kJ of

heat.

a) What is the enthalpy of combustion of C

H 2

OH(l)? 5

b)

Write the chemical equation for the combustion reaction.

c) What is

ΔH

o for 4CO

(g) + 6H 2

O(l) 2

→

2C

H 2

OH(l) + 6O 5

(g)? 2

12.

Use the data in Table 9.2 to estimate the enthalpies of the following reactions: a)

H

CBr 2

(g) + F 2

(g) 2

→

H

CF 2

(g) + Br 2

(g) 2

b) H

CI(g) + H 3

O(g) 2

→

H

COH(g) + HI(g) 3

c) HC

≡CH(g) + 2H

(g) 2

→

H

C-CH 3

(g) 3

d) CH

(g) 4

→

C(g) + 2H

(g) 2

13.

Use Table 9.2 to estimate the enthalpies of the following reactions: a)

H

C=CH 2

(g) + 3O 2

(g) 2

→

2CO

(g) + 2H 2

O(g) 2

b) 4CH

NH 3

(g) + 9O 2

(g) 2

→

4CO

(g) + 10H 2

O(g) + 2N 2

(g) 2

c) CCl

(g) + O 4

(g) 2

→

CO

(g) + 2Cl 2

(g) 2

d) 4HC

≡N(g) + 5O

(g) 2

→

4CO

(g) + 2H 2

O(g) + 2N 2

(g) 2

14.

Indicate

ΔS

o > 0,

ΔS

o ~ 0, or

ΔS

o < 0 for each of the following reactions:

a) 2H

(g) + O 2

(g) 2

→

2H

O(l) 2

b) HF(aq) + NO

1-(aq) 2

→

1- F

(aq) + HNO

(aq) 2

c) H

(g) + I 2

(g) 2

→

2HI(g)

d) CaCO

(s) 3

→

CaO(s) + CO

(g) 2

15.

Indicate

ΔS

o > 0,

ΔS

o ~ 0, or

ΔS

o < 0 for each of the following reactions:

a) H

CI(aq) + OH 3

1-(aq)

→

H

COH(aq) + I 3

1-(aq)

b) CCl

(l) 4

→

CCl

(g) 4

c) C

H 2

(g) + 2H 2

(g) 2

→

C

H 2

(g) 6

d) H

(g) + CO 2

(g) 2

→

H

O(g) + CO(g) 2

16.

Indicate the sign of

ΔG

o at low and high temperatures for each of the

following processes: a) NH

(g) + HCl(g) 3

→

NH

Cl(s) 4

Δ

oH

< 0

b) CaCO

(s) 3

→

CaO(s) + CO

(g) 2

Δ

oH

> 0

c) CH

OH(l) 3

→

CH

OH(g) 3

ΔH

o > 0

d) 2Cl

(g) + 7O 2

(g) 2

→

2Cl

O 2

(l) 7

ΔH

o > 0

Chapter 9 Reaction Energetics

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State

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