Enthalpy cycle question help please (Jan 2012)

Hi, It's the OCR Jan 2012 F322 paper, 3b)ii
http://www.ocr.org.uk/Images/78566-question-paper-unit-f322-chains-energy-and-resources.pdf

I get the basic enthalpy cycle questions, and for this question, once I know the values of the boxes I know how to get the final answer of the enthalpy change of formation. I just don't get how we find out the values of the different enthalpy changes of reactions from the table when they look so different in the table.

Please help :confused:

Thank you

Original post by monica95

Hi, It's the OCR Jan 2012 F322 paper, 3b)ii
http://www.ocr.org.uk/Images/78566-question-paper-unit-f322-chains-energy-and-resources.pdf

I get the basic enthalpy cycle questions, and for this question, once I know the values of the boxes I know how to get the final answer of the enthalpy change of formation. I just don't get how we find out the values of the different enthalpy changes of reactions from the table when they look so different in the table.

Please help :confused:

Thank you

Write out each step and remove the common terms from either side. They result will correspond to one of the equations in the boxes ...