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### Course: MCAT>Unit 5

Lesson 11: Principles of bioenergetics

# An analogy for Gibbs free energy

Continue to explore Gibbs free energy as you learn about the mathematical expression for delta G, and understand how enthalpy and entropy contribute to its overall sign. Unravel the mystery of spontaneous and non-spontaneous reactions, and see how temperature can tip the balance. A beach analogy brings it all home, connecting chemistry to everyday life. Created by Jasmine Rana.

## Want to join the conversation?

• I don't understand how to apply this analogy. Is it saying that at higher temperatures, delta S will tend to be positive, and that the forward reaction will occur spontaneously? and that at lower temperatures, delta H will tend to be positive, meaning the forward rxn isn't spontaneous?
• Ditch the analogy and just focus on the values of H and S in the chart. The analogy is a bit convoluted for the very simple terms outlined in the equation for G.
• For those who didnt get the analogy. When ΔS is positive and ΔH is negative, a process is always spontaneous

When ΔS is positive and ΔH is positive, the relative magnitudes of ΔS and ΔH determine if the reaction is spontaneous. High temperatures make the reaction more favorable, because exothermicity plays a small role in the balance.

When ΔS is negative and ΔH is negative, the relative magnitudes of ΔS and ΔH determine if the reaction is spontaneous. Low temperatures make the reaction more favorable, because exothermicity is important.

When ΔS is negative and ΔH is positive, a process is not spontaneous at any temperature, but the reverse process is spontaneous.
• Am I the only one who didn't hate the analogy? I understand free energy pretty well, but sometimes get confused with the temperature variable and found her reasoning helpful. Yes, sometimes it's good to have a chemistry-based example, but I thought this was relatable and explains it correctly.
• I really liked it too, it's good to have a backup way of remembering something just in case you blank during the exam because of nerves.
• What is the state of the reaction when delta G =0?
• The system is then in a state of equilibrium.
• This video was quite convoluted and oversimplified. I had to forward through it in order to NOT confuse myself.
• The analogy she gave makes the entire thing much more confusing than it needs to be. I understand the intent, but it's a very basic, simple concept, and the mathematic illustration is a much more accurate, helpful, and understandable explanation than such a broad, unclear, and inapplicable analogy.
• very confusing and convoluted analogy
• Thanks for the great video. The analogy helped me very much!
• At , what if the temperature was negative? Or is the temperature measured in kelvin?
• Temperature is in Kelvin. If H is + and S is -, delta G will be positive for all temperatures. The only time temperature can help figure out if delta G will be + or - is when both H and S have the same sign.
• So the idea is to try and achieve a spontaneous reaction where ever possible?