Question

The internal energy of a gas is given by U = 1.5 pV. It expands from 100 cm³ to 200 cm³against a constant pressure of 1.0 × 10⁵ Pa. Calculate the heat absorbed by the gas in the process.

Answer 1

Let change in volume of the gas be ∆V. 
∆V = (200 − 100) cm³ = 100 cm³
     = 10⁻⁴ m³
p = 1 × 10⁵ Pa

Change in internal energy of the system, ∆U = 1.5 pV
∆U = 1.5 × 10⁵ × 10⁻⁴ = 15 J
∆W = p∆V
      = 10⁵ × 10⁻⁴ = 10 J

Using the first law of thermodynamics, we get

∆Q = ∆U + ∆W = 10 + 15 = 25 J

Thus, heat absorbed by the system is 25 J.