Using the following equation for the combustion of octane, calculate the heat of reaction for 100.0 g of octane. The molar mass of octane is 114.33 g/mole.
2 C8H18 + 25 O2 -> 16 CO2 + 18 H2O ,deltaH°rxn = -11018 kJ
I got- 4820kJ but the answer is 4820kJ.
why is the answer positive when the delta h is negative?
The heat of reaction in terms of heat of formation values === Heat of formation of products - heat of formation of reactants.
whereas,
Heat of reaction in terms of combustion === Heat of combustion of reactants - heat of combustion of products
This reverse notation is due to the fact that in heat of formation the desired species is in product side ( eg: for CO2 the equation is C + O2 ---> CO2 ) whereas for heat of combustion the desired value is on reactant side (eg: here the desired value is methane since we are calling it as heat of combustion of methane CH4 + O2 ----> CO2 + water.)
That is why while calculating through combustion values we use - (deltaH products - deltaH reactants)
Thank you, So, the answer is +4820 kJ
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