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

Options

A. 8900 J
B. 6400 J
C. 5400 J
D. 7900 J

Answer

B

Explanation

Key idea heat given to a system `(DeltaQ)` is equal to the sum of increases in the internal energy `(Deltau)` and the work done `(DeltaW)` by the system against the surrounding and 1 cal =4.2 J
According to first law of thermodynamics
`DeltaU=Q-W`
`=2xx4.2xx1000-500`
`=8400-500`
=7900 J