Heat of Combustion

[sl2obel2ts]

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Lets say H2 is combusted. Is Heat of combustion POSITIVE or NEGATIVE. Kaplan says it is Negative (Chem practice subject test #2 Q5). I was doing some practice test sets, they say positive. when I checked wiki, it is +286KJ/MOL.

it is ENERGY RELEASED. I am really confused.

 

[Mstoothlady2012]

Lets say H2 is combusted. Is Heat of combustion POSITIVE or NEGATIVE. Kaplan says it is Negative (Chem practice subject test #2 Q5). I was doing some practice test sets, they say positive. when I checked wiki, it is +286KJ/MOL.

it is ENERGY RELEASED. I am really confused.

Heat of Combustion is an exothermic reaction. So I would assume that the enthalpy would be negative.

Where did you find that value in wiki? Can you post the website?

 

[DRHOYA]

In a standard combustion rxn, heat is a product, so the delta-H would be negatice, showing an exothermic rxn. What was the rxn equation for the question? Were there any special rxn conditions?

 

[harrygt]

All combustion reactions are exothermic which means all of them have a negative delta H. As long as everyone knows that combustion reactions emit heat, therefore, they use positive numbers to talk about the energy [Which is obviously released]