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Heating value of liquid-gas mixture was tested with primus which has gas burner. In the initial state aluminum container with lid protected from the wind has temperature of 0 celsius and in it 0,54 kg of water and 0,82 kg of ice cubes. Mixture was then heated to 100 celsius. During the heating 0,022 kg of liguid-gas was consumed. Evaluate heating value on the basis on these data. What factors are likely to contribute to the fact that the heating value that you get diverges from the real Heating value? Just some hint please I think I could use equation of thermal energy $U=C(T)\Delta T$, but then what you need the masses of water and ice cubes for? I could not find any formulas for heating value, why?

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The reason your professor has specified a mixture of ice and water is to check that you know about latent heat of fusion. Your professor won't be amused if I say any more, but a quick Google should tell you what extra bit you need to do when calculating the heat required to get the water and ice to 100C. If you're still unsure please ask as a comment to this answer.

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So how you define heating value? I find with google only conpectual definition( en.wikipedia.org/wiki/Heat_of_combustion#Heating_value ) –  laovultai Oct 10 '12 at 9:28
    
The phrase "heating value" isn't used in Physics as far as I'm aware, but I woud guess that it means joules per kilogram of fuel burnt, so it's basically the enthalpy of combustion (en.wikipedia.org/wiki/Standard_enthalpy_change_of_combustion). –  John Rennie Oct 10 '12 at 9:32
    
For Example if we heat just ice(m=0,82kg) so that $\Delta T=100-0=100 K$ then is thermal energy $U=C(T)\Delta T=2,1 \cdot 100 = 210 J$? And secondly which one releases energy, this heated gas or melted ice? –  laovultai Oct 10 '12 at 11:28

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