Specific Heat of CO2 and Methane Combustion

Question

Hi,

Could you please confirm these estimations for me:

Knowing that the Energy of Combustion of CH4 is 50.1 KJ/Kg, and that the specific heat for the CO2 at 273.15 K is approximately 0.81 KJ/Kg*K; please, could you confirm that in order to increase the temperature of 1 liter of gas of CO2 at 273.15K and 100 KPa (density = 1.98 Kg/m^3, so 0.00198 Kg), from 273.15 K to 573.15 K, it is only needed to combust 0,0000096 Kg of CH4. It is supposed an ideal / isolated system, without heat looses.

Q = m * c * AT

Q = 0.00198 * 0.81 * 300 = 0.481 KJ

Then: 0.481 / 50.1 * 10^3 = 9.6 * 10^-6 Kg, approximately just 0.015 liter.

It seems to be a very little portion of CH4 to me.

Thanks for your help.

PS – I apologize for my English, I am learning it.

Answer 1

with a density of 1.98Kg/m3,  you are right in that there are 0.00198 kg to be heated in that 1 litre

Q = m * c * AT

Q = 0.00198kg  (0.81kJ / kg-K)  (300K)

does give that  0.481 KJ are required

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and you are also right that if the Heat of combustion is 50.1 MegaJoules/ kg, then it is also 50.1*10^3 kJ / kg, so :

Then: 0.481 / 50.1 * 10^3 = 9.6 * 10^-6 Kg,

I believe you are right