Discussion 4: Thermodynamics
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The 1st Law of Thermodynamics
A cylinder with a moveable piston is entirely insulated from the environment surrounding it. The piston is pushed downward.
- Is the work done on the gas positive, negative or zero?
- Does the thermal energy of the gas increase, decrease, or stay the same?
- Explain your reasoning for question 2.
- Does the temperature of the gas change?
- Explain your reasoning for question 4.
The insulation around the cylinder is now removed and the piston is fixed in place so that it cannot move. The cylinder is initially at room temperature but is then placed in boiling water. After some time, thermal equilibrium is reached.
- Describe what happens to the gas in terms of: temperature, thermal energy, pressure, volume. Do these quantities increase, decrease, or stay the same?
- Explain your reasoning for question 6.
- Sketch this process on a pressure-Volume diagram.
- Is work done on the gas?
- Describe what allowed or prevented work to be done on the gas.
Consider two identical cylinders with pistons. One contains hydrogen gas and the other contains oxygen gas. They are have been allowed to reach thermal equilibrium with the result that the pistons are at the same height. The total mass in each cylinder is the same for both gases.
- Compare the volumes of the hydrogen and oxygen gases.
- Compare the temperatures of the hydrogen and oxygen gases.
- Compare the pressures of the hydrogen and oxygen gases.
- Compare the number of moles of the hydrogen and oxygen gases.