The internal energy change in a system that has absorbed 2 kcals of heat

The internal energy change in a system that has absorbed 2 kcals of heat and done 500J of work is:

Options

(a) 6400 J
(b) 5400 J
(c) 7900 J
(d) 8900 J

Correct Answer:

7900 J

Explanation:

According to first law of thermodynamics Q = ∆U + W
∆U = Q – W = 2 x 4.2 x 1000 – 500 = 8400 – 500 = 7900 J

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