Question

The latent heat of vaporisation of water is 2,240 J. If the work done in the process of vaporisation of 1g is 168 J, then the increase in internal energy is?

(a) 2408 J

(b) 2240 J

(c) 2072 J

(d) 1904 J

The question was posed to me in an interview for job.

Question is taken from Specific Heat and Thermodynamics topic in division Kinetic Theory of Gases of Engineering Physics I

Answer 1

Right choice is (c) 2072 J

Easy explanation: From the first law of thermodynamics,

dQ = mL = dU + dW

dU = m L – dW = 1×2240-168

dU = 2072 J.