IB chemistry past paper

Hi, can I ask why is A not B? ;;-;; I calculated B but the answer is A.
Thank you very much!!!

Hi!

Maybe since the values given are to calculate the enthalpy of reaction for 2NO+O2=2NO2 and not for NO+ 1/2 O2=NO2 so we must divide the enthalpy of products and reactants by 2.
enthalpy reaction = 1/2 enthalpy products - 1/2 enthalpy reactants = -57 kJ

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Yup I also think like you, thank you so much!!!

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