In an experiment, 108 J of work was done on a closed system. During this phase of the experiment, 79 J of heat energy was added to the system. What was the total change in the internal energy of the system?

187 J

Explanation:

First Law of Thermodynamics:

ΔQ = ΔW + ΔU

ΔQ : Heat. If it added to system then positive and if it is rejected by system then negative.

ΔW : Work. If it done by the system then positive and if it is done on system then negative.

ΔU : Internal Energy. If it positive then temperature of system increased and if it is negative then temperature of system decreased.

ΔQ = 79 J

ΔW = - 108 J

ΔU = ?

substituting the value in the equation:

79 = - 108 + ΔU

∴ ΔU = 187 J