Question

A system releases 125 kJ of heat while 104 kJ work is done on the system. Calculate the change in internal energy.

Answer 1

ΔU = Q + W

where, 

• Q = Heat added to the system (negative if heat is released)
• WWW = Work done on the system (positive if work is done on the system)

Given,

• Q = −125 kJ (since heat is released)
• W = +104 kJ

ΔU = (−125) + (104)

ΔU = −21 kJ