Question

How should the enthalpy of an intermediate step be manipulated when used to produce an overall chemical equation?

Multiply the enthalpy by 1 if the chemical equation is reversed.
Multiply the enthalpy by –1 if the chemical equation is reversed.
Add 2 to the enthalpy if the coefficients must be doubled.
Add 2 to the enthalpy if the coefficients must be cut in half.

Answer 1

The enthalpy of an intermediate step when used to produce an overall chemical equation should be manipulated in this way:
Multiply the enthalpy by –1 if the chemical equation is reversed.
If the forward reaction requires energy, the reverse will produce energy.

Answer 2

Ans: Multiply the enthalpy by –1 if the chemical equation is reversed.

Enthalpy is a thermodynamic state function which represents the heat content of a system. For chemical reactions, enthalpy can be used to predict if the  reaction is endothermic or exothermic.

If the enthalpy of the reactants is greater than products, the reaction is exothermic. If the reactants have a lower enthalpy than products, then the reaction is exothermic.

For a multistep reaction, the enthalpy of the intermediate step should be multiplied by -1 if the chemical reaction needs to be reversed in order to get the overall reaction.