Calculate (a) q when a system does 54 J of work and its energy decreases by 72 J and (b) △E for a gas that releases 38 J of heat and has 102 J of work done on it?

Answer 1

∆U = q + w

∆U = change in internal energy = -72 J

q = heat = ?

w = work = -54 J (negative because system is doing work on surroundings)

-72 J = q - 54 J

q = -18 J

∆U = q + w

∆U = ?

q = -38 J (negative because system releases heat)

w = +102 J (positive because work is done on the system by the surroundings)

∆U = -38 J + 102 J

∆U = 64 J