Question

(e) Estimate the total entropy change of the universe if: (i) a loose 3kg tile falls off a 20m-high-roof to the ground on a winter day (5) (ii) an electric kettle brings a litre of water to boil on a summer day. [5]

Answer 1

(i)mass of tile= m =3.0kg dropin height=h= 20m when the tile hits theground all of its kinetic energy changes to heat energy of tile heat added to the massof tile= Q= mgh g=9.8- we plug the know values in therelation gives =>Q=588J temperature on w int er day, T=10C=283K dQ change in entropy of tile=AS, +2.078- K tile the chang ein the entory of the ground is neglegible, and hence net chang ein the entropy of the universe=|AS, +2.078- K uni (ii) water initial temperature on summer day=30C=303K if the water reach boiling temperature after heating, chang ein temperature of water=AT=373K – 303K=70K summer day temperature =T=30C=303K mass of 1 liter water = m =1.0 kg water specific heat= S =4186, kg.C we plug the know values in the relation gives dQ mSAT = 980.9: K changein entropy of water after boiling =dS, water -dSa 980.9 - K total change in entropy of universe=dS, uni water