Chapter 10, Problem 29A

Interpretation Introduction

Interpretation: The fermentation of glucose to alcohol and carbon dioxide need to be identified as exothermic or endothermic if the enthalpy change for the reaction is -67 kJ.

  ${\text{C}}_{\text{6}}{\text{H}}_{\text{12}}{\text{O}}_{\text{6(aq)}}\stackrel{}{\to }{\text{2C}}_{\text{2}}{\text{H}}_{\text{5}}{\text{OH}}_{\text{(aq)}}{\text{+ 2CO}}_{\text{2(g)}}^{}$

Concept Introduction: On the basis of energy change during the chemical reaction, they can be classified as endothermic and exothermic reactions.

An exothermic reaction can be defined as the chemical reactions in which the energy is released whereas in an endothermic reaction, reaction proceeds with absorption of energy.

Answer to Problem 29A

It is an exothermic reaction and energy is released.

Explanation of Solution

Given information:

  ${\text{C}}_{\text{6}}{\text{H}}_{\text{12}}{\text{O}}_{\text{6(aq)}}\stackrel{}{\to }{\text{2C}}_{\text{2}}{\text{H}}_{\text{5}}{\text{OH}}_{\text{(aq)}}{\text{+ 2CO}}_{\text{2(g)}}^{}\Delta \text{H = - 67 kJ}$

The enthalpy change for the fermentation of glucose to carbon dioxide and alcohol is given as -67 kJ. Here the negative sign indicates that heat is released during the reaction. This is because the enthalpy change is the difference of enthalpy of product and reactant. If the enthalpy change for a reaction is negative it stands that the enthalpy change for product must be lesser than reactant.

Thus it must be exothermic process and energy is released because heat is released that decreases the enthalpy of product compare to reactant.

Conclusion

An exothermic reaction proceeds with release in energy.