Question

If 500 cal of heat are added to a gas, and the gas expands doing 500 J of work on its surroundings, what is the change in the internal energy of the gas?

Answer 1

The change in the internal energy of the gas 1,595 J

Step-by-step explanation:

The first law of thermodynamics establishes that in an isolated system energy is neither created nor destroyed, but undergoes transformations; If mechanical work is applied to a system, its internal energy varies; If the system is not isolated, part of the energy is transformed into heat that can leave or enter the system; and finally an isolated system is an adiabatic system (heat can neither enter nor exit, so no heat transfer takes place.)

This is summarized in the expression:

ΔU= Q - W

where the heat absorbed and the work done by the system on the environment are considered positive.

Taking these considerations into account, in this case:

• Q= 500 cal= 2,092 J (being 1 cal=4.184 J)

• W=500 J

Replacing:

ΔU= 2,092 J - 500 J

ΔU= 1,592 J whose closest answer is 1,595 J

The change in the internal energy of the gas 1,595 J