Визначення вільної енергії Гіббса

Gibbs Free Energy is the energy released from a chemical reaction that has the ability to do work. The amount of free energy is calculated from $$\Delta G = \Delta H - T \Delta S$$

Where $\Delta G$ is the value of Gibbs Free Energy, $\Delta H$ is the enthalpy of the reaction, $T$ is the temperature the reaction is occurring at and $\Delta S$ is the entropy change of the reaction.

NOTE: $\Delta S$ is usually expressed in Joules, and $\Delta H$ is usually expressed in kilojoules, so be sure to convert

When under standard conditions, the reaction can be rewritten as: $$\Delta G^{\circ} = \Delta H^{\circ} - T\Delta S^{\circ}$$

Just as reminder, standard conditions are:

For Solids: The Pure solid

For Liquids: The Pure liquid

For Gases: The gas at 1 atm

For Solutions: A 1M solution

For elements in standard state: These are zero.

When not under standard conditions, \Delta G can be calculate through the formula:$$\Delta G = \Delta G^{\circ} + RTlnQ$$

Where $R$ is the ideal gas constant (8.314 $\frac{J}{mol\cdot K}$) and $Q$ is the reaction quotient of the reaction at its initial conditions.

To calculate Gibbs Free Energy at equilibrium, the formula:$$\Delta G^{\circ}=-RTlnK$$ can be used, where $K$ is the equalibrium constant.

(Video) Gibbs Free Energy

by Bozeman Science

In this video, Mr. Andersen shows you how a change in enthalpy, entropy, or temperature can affect the available energy in a system. With this knowledge, you will be able to understand how a $\Delta G < 0$ is a spontaneous (exergonic) reaction, $\Delta G > 0$ is a backwards spontaneous (endergonic) reaction, and $\Delta G = 0$ is equilibrium. Finally, he explains free energy in terms of photosynthesis and cellular respiration.