Question

If the ΔH for

2Na + Cl2 → 2NaCl

is −772 kJ, what is the ΔH for this reaction:

2NaCl → 2Na + Cl2

Answer 1

ΔH2=772 kJ

Step-by-step explanation:

Hello,

In this case, since the change in a reaction's enthalpy is given by the subtraction between the product's enthalpies and the reactant's enthalpies, we notice that the second reaction is the same initial reaction but arranged on the contrary way. In means that if the original reaction has:

ΔH1=−772 kJ

It means that the reaction:

2NaCl → 2Na + Cl2

Has an enthalpy of reaction of:

ΔH2=-(−772 kJ)

ΔH2=772 kJ

As the reactants and products were all inverted, so the enthalpy change has the same number but different sign.

Best regards.