Question

Determine whether each of the following statements about the thermodynamic functions are True or False as they apply to chemical reactions.

1.The heat of reaction at constant volume is never equal to the heat of reaction at constant pressure.

2.All spontaneous chemical reactions have negative entropy changes.

3.The entropy change does not effect spontaneity.

4.Enthalpy and temperature are multiplied in the Gibbs free energy.

5.Spontaneity is increased by negative enthalpy changes.

Answer 1

1). True, Heat of the reaction at constant volume is internal energy change of the reaction and heat of the reaction at constant pressure is the enthalpy change of the reaction. They are not equal at all. Enthalpy change of the reaction is denoted by and Internal energy of the reaction is denote by . And the thermodynamic relation between these two quantities is given by

. Hence they are not equal.

2) False, All spontaneous chemical reaction have positive entropy changes. according to the thermodynamics relation.

For a spontaneous reaction, is a negative quantity and for this, should be negative and must be positive quantity so that the whole term becomes negative i.e. ( ). Thus for a spontaneous reaction, must be a positive quantity.

3). Incorrect Statement. According to the above discussion, affects the spontaneity. is negative for non-spontaneous and is positive for spontaneous.

4). Incorrect Statement. As discussed ,it is , which is multiplied with temperature 'T' but not the term .

5). True, spontaneity is increased by negative enthalpy change. According to the relation , more negative the enthalpy more negative will be the and hence increase the spontaneity. Higher negative value of indicates a higher spontaneity of the chemical reaction.