Calculate the internal energy change in each of the following cases .
(a) A system absorbs `5kJ` of heat and does `1kJ` of work
(b) `5kJ` of work is done on the system amd `1kJ` of heat is given out by the system .

Explanation

a. Here `q =+5kJ, w =+ 1kJ`
Therefore, according to the first law of thermodyanimics
`DeltaU =q -w =5 -1 = 4 kJ`
b. Here `w =- 5kJ, q =- 1kJ`
Therefore, according to first law of termodyanamics
`DeltaU =q -w =-1 -(-5) =4kJ`
i.e., the internal energy of the system increases by `4kJ` in each case.