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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Joseph on March 24, 2010, 07:15:24 AM

Title: Energy density & heat released on combustion - need some clarification
Post by: Joseph on March 24, 2010, 07:15:24 AM

Hi,

I am analyzing the energy of different fuels. I have several fuels and for each fuel I have the energy density and the energy that is released from heat of combustion. The way I understand energy density is the energy that a substance has per unit so ethanol for example has an energy density of 28000kJ/kg which means for every kilogram, there is 28000kJ of energy. Is my understanding of this correct?

Anyway, the heat energy released from combustion is always more than the energy density. Why is this so? I would have thought it would have been the other way around.

Thanks for your replies

Title: Re: Energy density & heat released on combustion - need some clarification
Post by: Astatine on April 23, 2010, 02:40:59 PM

Yes, energy density is the amount of energy released when a unit mass of the fuel is burnt.
28000kJ/kg implies that 28000kJ of energy is released when 1 kg of it is burnt.

The heat energy released depends on the mass of fuel burnt. If the mass of the fuel burnt is 0.01kg, the value is lower than the energy density.

Title: Re: Energy density & heat released on combustion - need some clarification
Post by: Joseph on May 14, 2010, 06:40:28 AM

Thanks for confirming that for me  :)