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Gas, Entropy Changes, Temperature

1. A 4 L sample of a diatomic gas with specific heat ratio 1.4, confined to a cylinder, is carried through a closed cycle. The gas is initially at 1 atm and 300 K. First, its pressure is tripled under constant volume. Then, it expands adiabatically to its original pressure. Finally, the gas is compressed isobarically to its original volume. Draw a P-V diagram of this cycle. Find the temperature of the gas at the start of the adiabatic expansion. Determine the volume of the gas at the end of the adiabatic expansion. Find the temperature at the end of the cycle. What is the net work done on the gas for this cycle?

2. One mole of H2 gas is contained in the left-hand side of the container, which has equal volumes left and right. The right-hand side is evacuated. When the valve is opened, gas streams into the right-hand side. What is final entropy change of the gas? Does the temperature of the gas change?

3. A 1.5 kg iron horseshoe initially at 600ºC is dropped into a bucket containing 20 kg of water at 25ºC. What is the final temperature if 100 g of water boils away? Ignore the specific heat of the container. (Specific heat of iron is 0.107 Cal/g*C. Latent heat of water vaporization is 540 cal/g)

4. Calculate the change in entropy of 250 g of water heated slowly from 20ºC to 80ºC.

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Answers to questions on work done on gas, entropy changes, temperature.

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