Question

200g water is heated from 40°C to 60°C. Ignoring the slight expansion of water, the change in its internal energy is close to ______.

(Given specific heat of water = 4184 J/kgK)

Options

• 167.4 kJ

• 8.4 kJ

• 4.2 kJ

• 16.7 kJ

Answer 1

200g water is heated from 40°C to 60°C. Ignoring the slight expansion of water, the change in its internal energy is close to 16.7 kJ.

Explanation:

Volume of water does not change, no work is done on or by the system (W = 0).

According to first law of thermodynamics,

Q = ΔU + W

Boiling of water is an isochoric process. So W = 0 i.e.,

Q = ΔU

ΔU = μcdT = 2 × 4184 × 20 = 16.7 kJ.