A piece of copper of mass `m = 90 g` at a temperature `t_1 = 90 ^@C` was placed in a calorimeter in which ice of mass `50 g` was at a temperature `-3 ^@C`. Find the entropy increment of the piece of copper by the moment the thermal equilibrium is reached.

Explanation

`c =` specific heat of copper `= 0.39 (J)/(g. K)` Suppose all ice does not melt, then
heat rejected `= 90 xx 0.39 (90 - 0) = 3159 J`
Heat gained by ice `= 50 xx 2.09 xx 3 + x xx 333`
Thus `x = 8.5 gm`
The hypothesis is correct and final temperature will be `T = 273 K`
Hence change in entropy of copper piece
=`mc 1n (273)/(363) = - 10 J//K`.