A cylinder of gas is assumed to contains ( 11.2 mathrm{kg} ) of butane. If a normal family needs ( 20,000 mathrm{kJ} ) of energy per day for cooking, how long will the cylinder last if the enthalpy of combustion,
( Delta mathrm{H}=-2658 mathrm{kJ} / mathrm{mole} ) for butane.

molar mass of butane ( left(C_{4} n_{8}right)=58 g mid ) mol

( 58 mathrm{g} ) of ( mathrm{C}_{4} mathrm{H}_{8} ) gives ( 2658 mathrm{kJ} ) heat 

( therefore 11.2 mathrm{kg} ) of ( mathrm{c}_{4} mathrm{h}_{8} ) gives [ begin{aligned} =& frac{2658}{58} times 11200 &=513268.965 mathrm{} end{aligned} ] No. Of days thout cylinder lasts [ =frac{513628.965}{20000} ] [ =25 cdot 66 quad approx 26 operatorname{days}]