Free Energy

What makes a reaction spontaneous or non-spontaneous? What is Gibbs free energy, how is it calculated, and what does it indicate? View this presentation to learn about spontaneous processes and Gibbs free energy. Make sure to take notes on calculating this important quantity.

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Relating Enthalpy, Entropy, Temperature and Free Energy to Spontaneity

Earlier, you learned that the value of Gibbs free energy indicates the spontaneity of the reaction. If ΔG is negative, then the reaction is spontaneous. If ΔG is positive, then the reaction is non-spontaneous. If ΔG is equal to zero, then the reaction is in equilibrium. While this is true, the relationship is a little more complicated when predicting the spontaneity of a reaction. You will need to review the relationship between ΔH, ΔS, ΔG and temperature to determine spontaneity. The table below summarizes the conditions that related ΔH, ΔS, and ΔG to temperature.

ΔH	ΔS	ΔG	Spontaneity
Positive	Positive	Positive at low temperatures or Negative at high temperatures	Spontaneous at high temperatures
Negative	Positive	Negative	Spontaneous at all temperatures
Negative	Negative	Positive at high temperatures or Negative at low temperatures	Spontaneous at low temperatures
Positive	Negative	Positive	Non-spontaneous at all temperatures

 

Free Energy Review

Review your knowledge of spontaneous processes and Gibbs free energy in this non-graded activity. Answer each of the questions by following the instructions provided. Then, click SUBMIT to check your responses. Click on the interactivity thumbnail, and then click NEXT to get started.