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The internal energy change in a system that has absorbed 2 kcal of heat and done 500 J of work is
A
7900 J
B
8900 J
C
6400 J
D
5400 J
Detailed Solution
Heat absorbed: $Q = 2$ kcal $= 2\times1000\times4.2$ J $= 8400$ J
Work done by the system: W = 500 J
First law of thermodynamics: $Q = \Delta U + W$
$\Delta U = Q - W = 8400 - 500$
$\Delta U = 7900$ J
Work done by the system: W = 500 J
First law of thermodynamics: $Q = \Delta U + W$
$\Delta U = Q - W = 8400 - 500$
$\Delta U = 7900$ J