All GRE Subject Test: Chemistry Resources
Example Question #1 : Gibbs Free Energy
At , a reaction has a Gibb's free energy change of . If the enthalpy change of the reaction is , what is the entropy change of the reaction?
We can relate enthalpy, entropy, and Gibb's free energy using the Gibb's free energy equation:
Keep in mind that temperature must be in Kelvin. Since we know enthalpy and Gibb's free energy for the reaction, we can solve for the entropy change:
Example Question #2 : Gibbs Free Energy
Which of the following options indicates that a chemical reaction is unfavorable?
All of these
The sign of indicates the direction of a chemical reaction and determines if a reaction is spontaneous or not. A chemical reaction in which is considered to be a spontaneous reaction because it will proceed without requiring any outside energy. To approach this problem, we must consider the equation for the Gibbs free energy of a reaction, . A reaction is considered to be favorable when is negative. The second law of thermodynamics indicates that the entropy of the universe is spontaneously increasing. This corresponds to a positive .