Question

2) Calculate the internal energy change in each of the following cases:
a) A system absorbs 15kJ of heat and does 5kJ of work.
b) 5kJ of work is done on the system and 15kJ of heat is given out by the system.​

Answer 1

Answer:

According to first law of thermodynamics:

∆U= q + w

(i) q = + 15kJ

w= -5 kJ

Using above equation:

∆U = 15 + (-5) = 10 kJ

Thus, internal energy of the system increases by 10 kJ.

(ii) Here, w = + 5 kJ

(work done on the system is positive)

q = -15 kJ ( heat is given out, so negative)

∆U = -15 + (+5) = -10 kJ

Thus, the internal energy of the system decreases by 10 kJ.