Gibbs Free Energy - Entropy, Enthalpy & Equilibrium Constant K

The video begins by addressing the concept of Gibbs free energy and its relation to spontaneous processes. It poses questions about the sign of delta G (change in free energy) in different scenarios: less than zero for spontaneous processes, equal to zero at equilibrium, and greater than zero for non-spontaneous processes. The video clarifies that a negative delta G indicates a spontaneous process, zero at equilibrium, and positive for non-spontaneous processes. It also touches on the relationship between energy, entropy, and the tendency of natural processes to reach the lowest energy state. The key takeaway is that the sign of delta G determines the spontaneity and direction of a chemical reaction.

The video continues with a problem-solving approach, guiding viewers on how to calculate the change in Gibbs free energy (delta G) at 25 degrees Celsius. It introduces the formula delta G = delta H - T * delta S, where delta H is the change in enthalpy, T is the temperature in Kelvin, and delta S is the change in entropy. The video emphasizes unit conversion from joules to kilojoules and provides a step-by-step calculation that results in a negative delta G, indicating a spontaneous process. It also explains how to calculate delta G for a reaction using standard enthalpy and entropy values, leading to the conclusion that a negative delta G corresponds to a spontaneous reaction.

The video moves on to demonstrate how to calculate the free energy change of a reaction using standard free energy change of formation values. It outlines the process of calculating delta G by multiplying the moles of products and reactants by their respective standard free energy values and subtracting them. The example provided results in a negative delta G, confirming the spontaneity of the reaction. The video also cautions viewers to be careful with the coefficients and signs when performing such calculations.

The discussion shifts to thermochemical equations, explaining how the energy change associated with a reaction is typically expressed in kilojoules. It covers how multiplying coefficients in a balanced equation affects the total energy change and the importance of using kilojoules per mole when calculating non-standard delta G values. The video stresses the need for consistency in units when using the equation delta G = delta G° + RT ln Q, where Q is the reaction quotient, R is the gas constant, and T is the temperature in Kelvin.

The video tackles the calculation of free energy change for the decomposition of dinitrogen pentoxide into dinitrogen tetroxide and oxygen. It shows how to manipulate and combine two given equations to derive the target equation and then sum their adjusted free energy changes to find the overall delta G. The process involves reversing one equation and adjusting coefficients to match the target equation, followed by calculating the new free energy changes and adding them up to get the final result.

The video explains the implications of a negative standard free energy change on the direction of a reaction and its shift towards equilibrium. It states that a negative delta G indicates a spontaneous reaction that proceeds in the forward direction until equilibrium is reached, where delta G becomes zero. The video also discusses how the free energy change increases as the reaction progresses towards equilibrium from a negative value.

The video provides a method to estimate the boiling point of bromine using the enthalpy of vaporization and standard entropy values for the liquid and gaseous states. It demonstrates the calculation using the equation delta G = delta H - T * delta S, where at the boiling point, delta G is zero, and the system is in equilibrium. The calculation results in the boiling point temperature of bromine, which is approximately 59 degrees Celsius.

The video discusses the relationship between delta G, reaction spontaneity, and the equilibrium constant (K). It explains that a negative delta G corresponds to a spontaneous reaction with K > 1, a positive delta G to a non-spontaneous reaction with K < 1, and a delta G of zero indicates equilibrium with K = 1. The video also addresses the concept that a large K value indicates a product-favored reaction at equilibrium.

The video shows how to calculate the standard free energy change (delta G) at 298 Kelvin using the equilibrium partial pressure constant (Kp). It uses the formula delta G = -RT * ln K, where R is the gas constant and T is the temperature in Kelvin. The calculation results in a positive delta G, indicating a reactant-favored reaction, and the video concludes that delta G is positive when K is less than one.

The video concludes with a method to calculate the equilibrium constant (K) for a reaction given its standard free energy change at 298 Kelvin. It uses the relationship delta G = -RT * ln K and rearranges the formula to solve for K. The video emphasizes the importance of using the correct units for delta G and temperature and provides a step-by-step calculation that results in a large K value, indicating a product-favored reaction.

The video addresses the spontaneity of the physical reaction of liquid water turning into ice. It explains that the freezing of water is an exothermic process with a negative delta H and a negative delta S, as entropy decreases from liquid to solid. The video uses a decision table to show that the spontaneity of such a reaction depends on temperature: it is spontaneous at low temperatures, at equilibrium at the freezing point, and non-spontaneous at high temperatures.