Enthalpy and Hess's law?

Question

when calculating the enthalpy value (using Hess's law) to find the change in enthalpy of one reaction by combining 3 others, is it ok not to use one of the below reactions? Can using 2 of the 3 reactions be ok if it still makes the target or main reaction?

Answer 1

You want to be careful - one of the reactions that you want to miss out might be a change of state. Look at the state symbols of the target equation.