An isothermal process is a thermodynamic process in which the temperature of the system remains constant. Here are a few common examples:
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Ideal Gas Expansion: When a gas expands slowly in a piston while being kept in contact with a heat reservoir at a constant temperature, it is undergoing an isothermal expansion. For instance, if you heat a gas in a piston to maintain its temperature while it expands, no change in temperature occurs.
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Phase Change of Water: During the boiling of water at 100°C (under normal atmospheric pressure), the temperature remains constant as the water changes from liquid to vapor. The heat energy added is used for the phase change instead of raising the temperature.
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Refrigeration Cycle: Inside a refrigerator, the refrigerant evaporates and absorbs heat from the inside compartment. This process can be considered isothermal because the refrigerant remains at a constant low temperature during the heat absorption, effectively cooling the refrigerator’s interior.
In each of these examples, the key characteristic is that the temperature does not change, which allows for specific thermodynamic calculations and applications.