Chemistry and Compression of Gas

Question

A gas is compressed 3 L while a constant external pressure of 1.2 atm is applied. What would the total change in internal energy be if 30.2 J of heat is released from the system after the compression?

Answer 1

Consider the first law of thermodynamics: ∆U = Q - W where ∆U is the change in internal energy, Q is heat and W is work. Also recall that work (W) = -P∆V when pressure is constant. From these equations, we confined ∆U of the system.

Q = -30.2 J (negative because heat is released from the system)

W = -P∆V = (-1.2 atm)(3 L) = -3.6 L-atm

Converting to joules: -3.6 L-atm x 101.3 J/1 L-atm = -364.8 joules

∆U = Q - W = (-30.2 J) - (-364.8 J) = +334.6 J