1. Gibb's Free Energy is
a. the spontaneous energy of a reaction ***
b. the chemical energy that can be used for performing work
c. the non-spontaneous energy of a reaction
d. the amount of activation energy needed for a reaction to start
2. Which reaction below is spontaneous at SATP?
a. ∆Hº=34.1 kJ and ∆Sº=46.2 J/K
b. ∆Hº=43.7 kJ and ∆Sº=-12.1 J/K
c. ∆Hº=25.0 kJ and ∆Sº=3.46 J/K
d. ∆Hº=10.8 kJ and ∆Sº=55.2 J/K ***
3. A reaction is spontaneous. What can you conclude about the reverse reaction?
a. It must be endothermic.
b. It is non-spontaneous. ***
c. It must have a decrease in entropy.
d. It is in equilibrium.
1. To determine the answer, you need to know the definition and concept of Gibbs Free Energy (G). Gibb's Free Energy is the amount of energy available to do work in a system at constant temperature and pressure. It combines both the enthalpy change (∆H) and the entropy change (∆S) in a system. The equation for Gibbs Free Energy is: ∆G = ∆H - T∆S, where T is the temperature in Kelvin.
From the given options, the correct answer is a. Gibbs Free Energy (G) represents the spontaneous energy of a reaction because a negative value of ∆G indicates that the reaction will proceed spontaneously. This means that the reaction can happen on its own without any external influence.
2. To determine which reaction is spontaneous at SATP (Standard Ambient Temperature and Pressure), you need to compare the values of ∆Hº (enthalpy change) and ∆Sº (entropy change) for each reaction.
The correct answer is d. ∆Hº=10.8 kJ and ∆Sº=55.2 J/K. This is because for a reaction to be spontaneous at a given temperature, ∆G (Gibbs Free Energy) must be negative. Using the equation ∆G = ∆H - T∆S, a negative value of ∆G means that ∆H is negative and/or ∆S is positive. In this case, both ∆H and ∆S have the correct signs for spontaneity.
3. To conclude about the reverse reaction of a spontaneous reaction, you need to understand the concept of reversibility in chemical reactions.
The correct answer is b. The reverse reaction of a spontaneous reaction is non-spontaneous. This is because the spontaneity of a reaction is determined by the sign of the Gibbs Free Energy (∆G). If the forward reaction is spontaneous (with a negative ∆G), then the reverse reaction will be non-spontaneous (with a positive ∆G). In other words, a spontaneous reaction will not occur in the reverse direction without external influence, such as changing the conditions or providing energy.