Question

You need to calculate the enthalpy change (AHO) of the reaction A + B → C.How can the enthalpies given for the reaction steps below be combined to give the overall change in enthalpy?

Answer 1

Step-by-step explanation:

The question requires us to determine a proper equation to calculate the enthalpy change for the following reaction:

`A+B\rightarrow C`

Considering the generic reactions and their associated enthalpy change given:

`\begin{gathered} Reaction\text{ }1:A+B\rightarrow D\text{ }\Delta H_1^° \\ Reaction\text{ }2:C+(1)/(2)B\rightarrow D\text{ }\Delta H_2^° \end{gathered}`

According to Hess' Law, enthalpy is a function of state, which means it does not depend on the path by which reactants are converted to products. Using this definition, we can rearrange the reactions 1 and 2 given (and apply all the changes required to their associated enthalpy change) in order to obtain the required reaction, and then calculate the enthalpy change of the final reaction considering the rearranged enthalpies of reactions 1 and 2.

Our final objective is to obtain a chemical equation that presents 1 mol of reactants A and B on the left side, and 1 mol of product C on the right side.

First, let's guarantee that we will have product C by multiplying reaction 2 by -1:

`Reaction\text{ 2}*(-1):D\rightarrow C+(1)/(2)B\text{ }\Delta H_2^°=-\Delta H_2^°`

Next, we need to make sure that