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Question:

200 g of 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/kg/K)

8.4 kJ

167.4 kJ

4.2 kJ

16.7 kJ

Solution:

The correct option is B (16.7 kJ)

Since expansion is ignored, work done is zero and hence by the first law of thermodynamics, internal energy change equals heat supplied.
ΔU = Q = 0.2(4184)(20) J = 16.7 kJ