Given the thermodynamic equation: #CH_4(g) + O_2(g) rarr CO_2(g) + 2H_2O(l)# #;DeltaH_"combustion"^@=-891.2*kJ*mol^-1#..what energy would be evolved by combustion of a #96*g# mass of methane?

1 Answer
anor277
Feb 15, 2018

Well, let's try to represent the thermochemistry....

Explanation:

We combust methane gas with dioxygen....

#CH_4(g) + 2O_2(g) rarr CO_2(g) + 2H_2O(l) + 891*kJ#

I put in the standard value of combustion enthalpy because I think you are using #kcal*mol^-1#. And as it stands, we report the energy as a PRODUCT, and therefore we would write....

#DeltaH_"combustion of methane"^@=-891.2*kJ*mol^-1#
And with respect to methane we combust a molar quantity of...

#(96*g)/(16.04*g*mol^-1)=5.99*mol#

And given complete combustion...we get...

#Delta_"rxn"=5.99*molxx-891.2*kJ*mol^-1=-5333.9*kJ#

#=-5333.9*kJxx0.239*kcal*kJ^-1=-1274.8*kcal#

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