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.