Chapter 15, Problem 73A

Interpretation Introduction

Interpretation:

The sign of $\Delta H$ for endothermic and exothermic reaction is to be written.

Concept introduction:

Exothermic reaction: A reaction is exothermic if heat is released in the chemical reaction.

Endothermic reaction: A reaction is endothermic if heat is absorbed in the chemical reaction.

Answer to Problem 73A

For endothermic reaction, $\Delta H=negative$

For exothermic reaction, $\Delta H=positive$

Explanation of Solution

A reaction is endothermic if enthalpy of products is greater than reactants and exothermic when enthalpy of products is less than reactants.

As $\Delta H={{\displaystyle \sum H}}_{products}-{\displaystyle \sum H_{reac\tan ts}}$

Therefore,

$\begin{array}{l}\Delta H_{exo}=negative\\ \Delta H_{endo}=positive\end{array}$

Conclusion

The sign of $\Delta H$ is positive for endothermic reaction and negative for exothermic reaction.