Chapter 4, Problem 80QRT

Interpretation Introduction

Interpretation:

The standard formation enthalpy value for $MgS$ has to be calculated using the given values.

Concept Introduction:

Hess’s law is applied to calculate the enthalpy changes in a reaction. According to Hess’s law “The overall enthalpy change of a reaction is equal to the sum of the enthalpy changes involving in each and every individual steps in the reaction”. Thus if a reaction involves ‘n’ steps then enthalpy change $\Delta H^{\circ }$ of the reaction is,

$\Delta H^{\circ }=\Delta H^{\circ }{}_1+\Delta H^{\circ }{}_2+\Delta H^{\circ }{}_3\mathrm{......}+\Delta H^{\circ }{}_n$

Production of 1 mole of product from standard state elements is known as formation reaction.