Sptember 12th - Biology -Thermodynamics, Entropy, and Free Energy in Biochemical Reactions

What happens in an exothermic reaction?

Energy decreases; heat is released; products have lower energy than reactants.

What happens in an endothermic reaction?

Energy increases; energy is absorbed; products have higher energy than reactants.

What is entropy?

A measure of energy dispersion; energy not available to do work; generally increases as energy becomes more spread out.

What does the second law of thermodynamics state about the universe's total entropy?

The total entropy of the universe always increases.

How is total entropy defined in a process?

Total entropy = entropy of the system + entropy of the surroundings; the sum must increase.

What is free energy?

The portion of a system's energy that is available to do work in a given context.

What is the standard equation for free energy change under typical conditions?

ΔG = ΔH − TΔS (with ΔS referring to the total entropy change; temperature in Kelvin).

How do you determine if a reaction is spontaneous from ΔG?

If ΔG < 0, the reaction is spontaneous (exergonic); if ΔG > 0, it is non-spontaneous (endergonic).

Can enthalpy change alone determine spontaneity?

No; spontaneity depends on ΔG, which combines enthalpy and entropy (and temperature).

What happens to ΔG as a reaction approaches equilibrium in a cell?

ΔG approaches zero; net reaction slows and may stop unless products are removed or conditions shift to keep ΔG negative.

What is ΔG°' (standard free energy change)?

The free energy change under standard conditions, used as a reference for comparing reactions.

Why is ATP hydrolysis important for glycolysis?

Breaking ATP bonds provides energy to transfer a phosphate to glucose, forming glucose-6-phosphate; the overall process is energy-coupled to drive the reaction.

What is activation energy?

The energy barrier that must be overcome to break old bonds and form new bonds along the reaction pathway.

Why might a reaction in a cell not go to completion even if ΔG is negative?

Because not all reactants are converted; as reaction proceeds, ΔG becomes less negative and approaches zero; cells remove products to keep driving forward.