Last lesson we calculated that propane has an energy of combustion of 2220 kiloJoules per mole while hydrogen gas (rocket fuel) has an energy of combustion of 286 kiloJoules per mole. However, hydrogen gas has a much higher energy of combustion per gram than propane. Why is this?

c is having 4 valence electrons and is bonded to three hydrogens and one sulphur atom, therefore, the number of bond pair is equal to four. as all the valence electrons are used in forming the bonds so, there is no lone pair left on carbon.

s is having 6 valence electrons and is bonded to one other sulfur atom and one carbon atom, therefore, the number of bond pair is equal to 2. as only two valence electrons are used in forming the bonds so, four electrons are left. therefore, two lone pairs are present on s.