Download Chem 1010 Tutorials Tutorial 9A – Heat and Work Fall 2013

Chem 1010 Tutorials
Tutorial 9A – Heat and Work
Fall 2013
1.
A gas expands and does 287 J of work on its surroundings. At the same time, it absorbs 216 J of
heat from the surroundings. What is the change in the internal energy of the system?
2.
A system absorbs 272 kJ of heat and the surroundings do 125 kJ of work on the system. What is
the change in internal energy of the system?
3.
105 kJ of work is performed on a system during compression as it releases 625 kJ of heat. What
is the change in internal energy of the system?
4.
How much work is done on a balloon that is compressed from 6 L to half its original volume at
atmospheric pressure?
5.
During a breath, the average human lung expands by about 0.50 L. If this expansion occurs
against an external pressure of 1.00 bar, how much work is done during the expansion?
6.
A sample of an ideal gas in the cylinder of an engine is compressed from 400. mL to 50.0 mL
against a constant pressure of 8.00 bar. At the same time, 140 J of energy is transferred from
the gas to the surroundings as heat. What is the total change in internal energy of the gas?
7.
A sample of an ideal gas is allowed to expand from an initial volume of 0.200 L to a final volume
of 3.50 L against a constant pressure of 0.982 bar. At the same time, 117 J of heat is transferred
from the surroundings to the gas. What is the total change in internal energy of the gas?
8.
A gas is compressed from an initial volume of 5.55 L to a final volume of 1.22 L by an external
pressure of 1.00 bar. During the compression, the gas releases 124 J of heat. What is the
change in internal energy of the gas?
9.
A container was found to gain 97.3 kJ of heat when its temperature increased by 2.73 °C. What
is the heat capacity of the container?
10.
The heat capacity of a certain building is 3.6 x 1011 kJ·°C –1. How much heat is required to raise its
temperature from 15.0°C to 20.5°C?
11.
The specific heat of water is 4.184 J·g–1·°C –1. If a “system” consists of 453 g of water at 25.0°C,
how much heat is required to raise the temperature of the system to 100.0°C?
12.
a) What will be Tfinal of a system consisting of 325 g of water at 4.2°C if it absorbs 12.28 kJ of
heat?
b) What will be Tfinal of a system consisting of 115 g of water at 97.8°C if it emits 2496 J of heat?
13.
Given the following specific heats of metals:
Specific heat
Specific heat
Metal
Metal
(J·g–1·°C –1)
(J·g–1·°C –1)
Manganese
0.477
strontium
0.301
Sodium
1.225
aluminum
0.899
Metal
beryllium
Specific heat
(J·g–1·°C –1)
1.823
If the same amount of heat is added to 100.0 g samples of each of the metals which are all at
the same temperature, which metal will have the highest final temperature?
14.
In order to raise the temperature of a particular pond by 2.3 K, 5.2 x 1028 kJ of heat are required.
a) What is the mass of the pond? (specific heat of water is 4.184 J·g–1·°C –1)
b) What is the heat capacity of the pond?
c) How much heat would be given off if the temperature of the pond decreased by 3.9 degrees
Celsius?
15.
What is the quantity of heat required to raise the temperature of 12.5 L of water from 22.0 to
33.7°C? (Density of water is 1.00 g/mL ; its specific heat is 4.184 J·g–1·°C –1)
16.
When a 20.0 g block of gold absorbs 5.60 joules of heat the temperature of the block rises from
20.50°C to 22.67°C. What is the specific heat of gold?
17.
The specific heat capacity of iron metal is 0.430 J·g–1·°C –1. If a sample of iron evolves 29.0 kJ of
heat when it cools from 500.0 °C to 25.9°C, what is the mass of the iron sample?
18.
a)
A silver spoon has a specific heat capacity of 0.235 J·g–1·°C –1. If a spoon with a mass of
8.0 g at a temperature of 20.0oC is placed in an insulated mug containing 50.0 g of water
at 97.0oC, what will be the final temperature of the spoon and the water? (Water has a
specific heat capacity of 4.184 J·g–1·°C –1)
b)
If this was repeated with a gold spoon (Cs = 0.128 J·g–1·°C –1) at the same mass and initial
temperature, what would be the final temperature?
19.
A 32.5 g rod (Cs = 0.449 J·g–1·°C –1), initially at 22.7oC, is submerged into an unknown mass of
water at 63.2oC in an insulated container. The final temperature of the mixture is 59.5oC. What
is the mass of the water?
20.
A 2.74 g sample of a substance suspected to be pure gold is warmed to 72.1oC and submerged in
15.2 g of water initially at 24.7oC. The final temperature of the mixture is 26.3oC. Knowing that
the specific heat capacity of gold is 0.128 J·g–1·°C –1, could this solid be pure gold?
ANSWERS:
2
2
1. ΔU = –71 J
2. ΔU = 397 kJ
3. ΔU = 5.2 x 10 kJ
4. w = 3 x 10 J
5. w = –50. J
6. ΔU = 140 J
7. ΔU = –207 J
8. ΔU = 309 J
9. Ccalorimeter = 35.6 kJ/C°
10. q = 2.0 x 10 kJ
11. qsystem = 142 kJ
12. a) Tfinal = 13.2°C
b) Tfinal = 92.6°C
13. strontium
30
12
31
o –1
31
14. a) mpond = 5.4 × 10 g
b) Cpond = 2.3 × 10 J∙ C
c) qpond = −8.8 × 10 J
15. qsystem = 612 kJ
16. cgold = 0.129 J/g·C°
17. miron = 142 g
o
18. a) 96.3 C
o
b) 96.6 C
19. mwater = 35 g
–1 o –1
20. Cs = 0.82 J∙g ∙ C ; No