- #1
Bipolarity
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Heat is defined as "the transfer of energy owing to a temperature difference between two bodies".
Consider a gas expanding against a massless frictionless piston. Assume that the process is both isothermal and reversible, and that the gas is ideal, so that its internal energy does not change.
Since its internal energy does not change, the work done by the gas must be compensated by heat added to the gas.
However, we initially assumed that the gas was isothermal, i.e. in thermal equilibrium with its surroundings. So how can heat, by its definition, be added to the gas if its already in thermal equilibrium with its surroundings?
Obviously, the first law of thermo mandates the heat transfer, but the definition of heat contradicts this viewpoint.
Perhaps the definition of heat is only valid for isovolumetric processes?
BiP
Consider a gas expanding against a massless frictionless piston. Assume that the process is both isothermal and reversible, and that the gas is ideal, so that its internal energy does not change.
Since its internal energy does not change, the work done by the gas must be compensated by heat added to the gas.
However, we initially assumed that the gas was isothermal, i.e. in thermal equilibrium with its surroundings. So how can heat, by its definition, be added to the gas if its already in thermal equilibrium with its surroundings?
Obviously, the first law of thermo mandates the heat transfer, but the definition of heat contradicts this viewpoint.
Perhaps the definition of heat is only valid for isovolumetric processes?
BiP