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Question
Explain the change in internal energy of a thermodynamic system (the gas) by heating it.
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Solution
Consider a gas filled in a cylinder fitted with a massless, movable, and frictionless piston as shown in the figure.
Let Ts be the temperature of gas (system),
TE be temperature of environment.
Initially, the cylinder is heated using a burner, as illustrated in the picture. At this level, TE exceeds Ts. The temperature difference between the source of heat and the system causes energy to flow towards the gas in the cylinder. This increases the gas's internal energy. When the environment is cooler than the gas, Ts > TE, resulting in energy transfer from the gas to the surroundings.
The gas expands as a result of the piston being forced out during this procedure. The gas does a certain amount of work. The gas cools, and some of its energy is lost. This describes how exerting effort can alter a gas's intrinsic energy.
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