A thermodynamic system (gas in a vessel) passes from one state to another, transferring an amount of heat equal to Q

A thermodynamic system (gas in a vessel) passes from one state to another, transferring an amount of heat equal to Q to the environment. How has the internal energy of the system changed if the volume of gas does not change?

Since the process is isochoric, the work of the gas is zero, therefore: U = -Q = -20J.

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