I need help with problems 12/13 since they play off each other. Question 13 refe

Question

I need help with problems 12/13 since they play off each other. Question 13 references question 7-4 which I have included a picture of as well as my answer for for reference.

PROBLEM 8-12 Assuming that the energy released by combustion of H2 is proportional to the amount of oxygen it consumes, estimate the ratio of heat released by one mole of methane compared to one mole of hydrogen gas. PROBLEM 8-13 Using the thermochemical information in the H2 combustion equation, cal- culate the enthalpy (heat) of combustion of hydrogen per gram, and by com- paring it to that of methane (see Problem 7-4), decide which fuel is superior on a weight basis. By comparing the actual energy released by combustion per mole of gas-and hence per molar volume decide which fuel is superior on a volume basis.

Explanation / Answer

12.

CH4 + 2 O2 --> CO2 + 2 H2O : 2 moles of O2

H2 + ½ O2 --> H2O : ½ mol of O2

Ratio of heat released = 2 / ½ = 4

13.

a)

Using thermochemical information of 12,

Let amount of heat by H2 combustion = X

Amount of heat by H2 combustion / g of H2 = X / 2

Amount of heat by CH4 combustion = 4 X

Amount of heat by CH4 combustion / g of CH4 = 4 X / 16 = X / 4

Heat released by H2 combustion / g of H2 > Heat released by CH4 combustion / g of CH4

X / 2 > X / 4

Therefore, fuel H2 is superior on weight basis.

b)

From question 12, Heat of combustion of CH4 /mol > Heat of combustion of H2 /mol

Using actual heat of combustion of fuels,

Heat of combustion of H2 = 286 kJ/mol

Heat of combustion of CH4 = 889 kJ/mol

Heat of combustion of CH4 /mol > Heat of combustion of H2 /mol

Therefore, fuel CH4 is superior on molar or volume basis

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