All High School Chemistry Resources
Example Questions
Example Question #3 : Help With Gibb's Free Energy
Which of the following best describes the change in Gibbs free energy when a sample of ice is melting at a temperature of 21oC?
Always positive
Always negative
Sometimes positive
Sometimes negative
Positive or negative depending on the volume of the ice
Always negative
Gibbs free energy is used to determine if a reaction will occur spontaneously. If the Gibbs free energy is negative for the given process, then the reaction will occur spontaneously.
In the given scenario, ice will always melt spontaneously when the temperature is above 0oC. As a result, we can state that the Gibbs free energy will always be negative for this process.
Example Question #2 : Help With Gibb's Free Energy
If a process is endothermic and involves a decrease in entropy, when will it be spontaneous?
At high temperatures
Upon addition of a catalyst
Never
In zero gravity
At low temperatures
Never
.
If a process is endothermic, is positive.
If a process involves a decrease in entropy, is negative.
Under these conditions, the only way can be negative is if is below absolute zero, which is impossible. Catalysts do not effect , rather they only affect reaction kinetics, not thermodynamics.