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

(i) Here q + 5 kJ and w = - 1 kJ
`therefore` According to first law of thermodynamics, `Delta E=q+w=5+(-1)=4kJ`
(ii) Here w = + 5kJ and q = - 1kJ
`therefore` According to first law of thermodynamic `Delta E=q+w=-1+(+5)=4 kJ`
i.e. the internal energy of the system increases by 4 by in each case.