when 5 litres of a gas mixture of methane and propane is perfectly combusted at 0
and 1 atmosphere, 16 litre of oxygen at the same temperature and pressure is consumed
The amount of heat released from this combustion in kj [(AH comb (CH2) = 890 kJ mol-1
AH (CH2) = 2220 kJ mol-')] is
a) 32
b) 38
c) 317
d) 477
Answers
The balanced equations of combustion reactions are:
CH4(g)+2O2(g)→CO2(g)+2H2O(l),ΔHCH4(g)=890kJmol−1[1]
C3H8(g)+5O2(g)→3CO2(g)+4H2O(l),ΔHC3H8(g)=220kJmol−1[2] Let here be x L CH4 and (5−x)LC3H8 in 5L gas mixture at STP. So total volume of oxygen consumed as per stoichiometry of the reactions involved will be 2x+5(5−x)=16 ⇒2x+25−5x=16 ⇒3x=9 ⇒x=3L So volume of CH4(g)=3L and volume of C3H8(g)=2L at STP. So corresponding number of moles of gases present int 5 Lgas mixture can be obtained by dividing the volumes of gases at STP with 22.4L as any gas of 1mol occupies 22.4L at STP nCH4(g)=3L22.4L=322.4mol nC3H8(g)=2L22.4L=222.4mol So the amount of heat released due to combustion of the 5L gas mixture ΔHmixture=322.4ΔHCH4(g)+222.4ΔHC3H8(g) ⇒ΔHmixture=3×890+2×222022.4kJ≈317kJ