Concept 8.2: The free-energy change of a reaction tells us whether or not the reaction occurs spontaneously

Flashcards from Concept 8.2 of Pearson's Campbell Biology, Twelfth Edition.

Free energy (G)

The portion of a system’s energy that can do work when temperature and pressure are uniform throughout the system, as in a living cell

Delta G

The change in free energy, related to changes in temperature, total energy, and entropy

• Represents the difference between the free energy of the final state and free energy of the initial state

• Lower levels signify more stability after spontaneous expenditure

Spotaneous processes

Processes that use energy and increase total entropy

• Causes a negative change in free energy (negative delta G)

• Creates more stability in a system to work towards equilibrium

Nonspontaneous processes

Processes that build up or maintain total levels of energy or entropy

• Causes a zero or positive change in free energy (positive delta G)

• Used by the cell to perform work

Unstable systems

Systems with higher levels of free energy (G)

• Seen with a diver on a platform being less stable than in the water

Stable systems

Systems with lower levels of free energy

• Seen with a diver in the water after jumping off a platform, thus using energy

Equilibrium

The point at which forward and reverse reactions occur at the same rate, creating maximum stability

• Systems must nonspontaneously work to move away from equilibrium

• Eventually reached by closed or isolated systems, but never reached in an open living cell with flowing materials enabling work

Exergonic reaction

A reaction that creates a net release of free energy to the surroundings, causing energy to be expended outward

• Products store less free energy than reactants, creating a negative delta G and thus signifying a spontaneous reaction towards equilibrium

  • This releases potential energy

• G determines how much work a reaction can perform

Endergonic reaction

A reaction that absorbs free energy from the surroundings, causing energy to be drawn inward

• Products store more free energy than the reactants, creating a positive delta G and thus signifying a nonspontaneous reaction away from equilibrium

• Higher delta G amounts require more initial energy input

Catabolic pathway

A chain of reactions as seen in cellular respiration’s individual products becoming reactants for the next steps

• Steady glucose and waste progression ensure that equilibrium is never reached