18.3 Gibbs Free Energy and the Relationship between Delta G, Delta H, & Delta S | General Chemistry

Chad introduces the concept of Gibbs free energy in the context of his science education platform, Chad's Prep. He explains that Gibbs free energy (ΔG) is a thermodynamic potential used to determine the spontaneity of a process. The formula ΔG = ΔH - TΔS is presented, where ΔH is the change in enthalpy, T is the temperature, and ΔS is the change in entropy. Chad emphasizes that a negative ΔG indicates a spontaneous reaction, a positive ΔG indicates a non-spontaneous reaction, and ΔG equals zero at equilibrium. The distinction between standard Gibbs free energy (ΔG°) and non-standard conditions is also introduced, with a clarification that standard conditions typically refer to concentrations of reactants and products, not necessarily the temperature.

Chad discusses the derivation of Gibbs free energy, starting from the second law of thermodynamics which states that the total entropy change of the universe must be positive for a process to be spontaneous. He explains the mathematical transformation that leads to the formula ΔG = ΔH - TΔS, and highlights its significance in determining the spontaneity of a reaction without needing to measure the entropy change of the surroundings. Chad also underscores the importance of understanding this equation for students preparing for exams and further studies in thermodynamics.

This paragraph delves into the preferences of the universe regarding chemical reactions, focusing on the tendencies for spontaneous processes. Chad explains that the universe favors exothermic reactions (negative ΔH) and positive entropy changes (positive ΔS). He outlines scenarios where both, one, or neither of these conditions are met, and how they relate to the spontaneity of a reaction. Chad also introduces the concept that the universe tends toward lower energy states and increased disorder, which aligns with the principles of entropy and enthalpy changes.

Chad provides a mathematical perspective on the relationship between Gibbs free energy, enthalpy change, and entropy change. He discusses the outcomes of adding positive and negative numbers and how these principles apply to the formula ΔG = ΔH - TΔS. The explanation includes how the signs of ΔH and ΔS influence the spontaneity of a reaction, with a focus on the conditions that lead to a negative, positive, or zero ΔG. Chad also emphasizes the importance of understanding these mathematical relationships for predicting reaction spontaneity.

The role of temperature in determining the spontaneity of reactions is explored in this paragraph. Chad explains how different combinations of ΔH and ΔS values result in reactions being spontaneous at all temperatures, no temperatures, high temperatures, or low temperatures. He provides examples, such as the boiling of water and melting of ice, to illustrate the concept of threshold temperatures where ΔG equals zero. Chad also discusses the importance of understanding these temperature-dependent conditions for predicting and analyzing chemical reactions.

Chad demonstrates how to calculate the threshold temperature at which a reaction becomes spontaneous by setting ΔG to zero and solving for the temperature using the values of ΔH and ΔS. He uses the example of water's vaporization to show the calculation process and emphasizes the importance of unit consistency. Chad also points out common mistakes students make, such as not converting units correctly or misinterpreting the resulting temperature in Celsius instead of Kelvin.

In the concluding paragraph, Chad summarizes the importance of understanding Gibbs free energy and its relation to reaction spontaneity. He encourages students to practice and master these concepts, offering a general chemistry master course with over 1200 practice questions for further study. Chad also invites students to support the channel through likes and comments and wishes them happy studying as they continue their educational journey.