# Solving various thermodynamics questions

1 - The air in an inflated balloon (defined as the system) is warmed over a toaster and absorbs 130J of heat. As it expands, it does 76kJ of work. What is the change in internal energy for the system?

2 - A piston has an external pressure of 8.00 atm. How much work has been done in joules if the cylinder goes from a volume of 0.140 liters to 0.450 liters.

3 - A volume of 105mL of H2O is initially at room temperature (22.0∘C). A chilled steel rod at 2.00∘C is placed in the water. If the final temperature of the system is 21.3∘C, what is the mass of the steel bar?

Use the following values:

specific heat of water = 4.18 J/(g∘C)

specific heat of steel = 0.452 J/(g∘C)

4 - The specific heat of water is 4.18 J/(g∘C). Calculate the molar heat capacity of water.

5 - It takes 47.0J to raise the temperature of an 11.3g piece of unknown metal from 13.0∘C to 24.1∘C. What is the specific heat for the metal?

6 - The molar heat capacity of silver is 25.35 J/mol∘C . How much energy would it take to raise the temperature of 11.3g of silver by 19.0∘C ?

7 - What is the specific heat of silver?

8 - If this expansion occurs against an external pressure of 1.0 atm, how much work (in J ) is done during the expansion?

9 - A gas is compressed from an initial volume of 5.40L to a final volume of 1.20L by an external pressure of 1.00 atm . During the compression the gas releases 128J of heat.

What is the change in internal energy of the gas?

10 - A mole of X reacts at a constant pressure of 43.0 atm via the reaction

X(g)+4Y(g)→2Z(g), ΔH ∘ =−75.0 kJ

Before the reaction, the volume of the gaseous mixture was 5.00 L . After the reaction, the volume was 2.00 L . Calculate the value of the total energy change, ΔE , in kilojoules.

11 - The change in internal energy for the combustion of 1.0 mol of octane at a pressure of 1.0 atm is 5084.2kJ .If the change in enthalpy is 5074.4kJ how much work is done during the combustion?

12 - What mass of natural gas (CH 4 ) must you burn to emit 267kJ of heat?

CH 4 (g)+2O 2 (g)→CO 2 (g)+2H 2 O(g) ΔH ∘ rxn =−802.3kJ

13 - Determine the mass of CO 2 produced by burning enough carbon (in the form of charcoal) to produce 530kJ of heat.

C(s)+O 2 (g)→CO 2 (g)ΔH ∘ rxn =−393.5kJ

14 - In the following experiment, a coffee-cup calorimeter containing 100 mL of H 2 O is used. The initial temperature of the calorimeter is 23.0 ∘ C If 5.70g of CaCl 2 is added to the calorimeter, what will be the final temperature of the solution in the calorimeter? The heat of solution ΔH soln of CaCl 2 is −82.8 kJ/mol.

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#### Solution Preview

1-The air in an inflated balloon (defined as the system) is warmed over a toaster and absorbs 130J of heat. As it expands, it does 76kJ of work. What is the change in internal energy for the system?

Answer:

ΔE=q+w

Anything absorbed is + and any SYSTEM doing work is - .

130J + - 76000J= -7.587 x 10 ^ 4.

2-A piston has an external pressure of 8.00 atm How much work has been done in joules if the cylinder goes from a volume of 0.140 liters to 0.450 liters.

Answer:

(0.450 - 0.140) x 8.0=2.48 J

3-A volume of 105mL of H 2 O is initially at room temperature (22.0 ∘ C ). A chilled steel rod at 2.00 ∘ C is placed in the water. If the final temperature of the system is 21.3 ∘ C , what is the mass of the steel bar?

Use the following values:

specific heat of water = 4.18 J/(g⋅ ∘ C)

specific heat of steel = 0.452 J/(g⋅ ∘ C)

Answer:

105 x 4.18 x 22 + MS x .452 x 2 = 105 x 4.18 x 21.3 + MS x .452 x 21.3

MS = mass of steel

Solve for MS.

energy gained by the steel = the energy given up by the water

MS x .452 x [21.3 -2] = 105 x 4.18 x [22 - 21.3]

mass of steel = 35.22 g

4-The specific heat of water is 4.18 J/(g⋅ ∘ C) . Calculate the molar heat capacity of water.

Answer:

specific heat of water is 4.18 J/g-K

mole of water = 1802 g

molar heat capacity = (4.18 ...

#### Solution Summary

The various thermodynamics questions are solved. The specific heat of solvers are given.

Thermodynamics Questions: Problems on Heat Exchange

See attached file for graphs.

1. Dry ice is frozen carbon dioxide. If you have 1.8 kg of dry ice, what volume will it occupy if you heat it enough to turn it into a gas at a temperature of 20°C?

2. How much work is done on the gas in the process shown in the figure?

3. If a person has a dangerously high fever, submerging her in ice water is a bad idea, but an ice pack can help to quickly bring her body temperature down. How many grams of ice at 0°C will be melted in bringing down a 68 kg patient's fever from 40°C to 39°C?

4. Seals may cool themselves by using thermal windows, patches on their bodies with much higher than average surface temperature. Suppose a seal has a 0.030 m^2 thermal window at a temperature of 30°C. If the seal's surroundings are a frosty -20°C, what is the net rate of energy loss by radiation? Assume an emissivity equal to that of a human.

5. What is the tension in the string in the figure?

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