HW #115e

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Shannon Han 2B
Posts: 48
Joined: Fri Sep 26, 2014 2:02 pm

HW #115e

Postby Shannon Han 2B » Tue Jan 13, 2015 9:29 pm

On 115e, the questions asks to calculate the quantity of heat per mole of CO2 produced for methane, ethanol, and octane. I got this quantity correct for methane and ethanol but when I tried doing -5471/2 moles CO2, I got a different answer than the solution manual. Are we not supposed to use 5471? Also, how do we know which process produces less or more CO2 in the environment for each kilojoule generated?

Niharika Reddy 1D
Posts: 127
Joined: Fri Sep 26, 2014 2:02 pm

Re: HW #115e

Postby Niharika Reddy 1D » Tue Jan 13, 2015 11:45 pm

If you write our the combustion reaction for octane and balance it, 8 moles of CO2 are produced. (The stoichiometric coefficients of octane, oxygen gas, carbon dioxide, and water are 1, 25/2, 8, and 9 respectively).

You still use the enthalpy of combustion of octane, -5471 kJ, but divide it by 8 since 8 moles of CO2 are produced.

Shannon Han 2B
Posts: 48
Joined: Fri Sep 26, 2014 2:02 pm

Re: HW #115e

Postby Shannon Han 2B » Wed Jan 14, 2015 10:18 am

Oh okay I forgot to write that balanced equation. Do you understand why it's less CO2 for methane and more CO2 for ethanol and octane?


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