AP Chemistry Notes Essay Example

do not need to be included in the expression for K. Gases are represented by their partial pressures in ATM while species in water solution are represented by their molar concentrations. The numerical value of equilibrium constants can be calculated using the partial pressures of reactants and products at equilibrium, and any changes in these values as the system approaches equilibrium are linked through the balanced equation coefficients. Finally, it is possible to determine the feasibility of a reaction knowing only the magnitude of the equilibrium constant.If K is very small, the equilibrium mixture will contain mostly starting material and the reaction will not go in practical terms. If K is large, the reaction will produce products in high yield. In cases where K has an intermediate value, quantitative calculations must be made regarding the direction or extent of the reaction. The reaction quotient, Q, has the same expression as the equilibrium constant, K, but with partial pressures at a specific moment, not necessarily at equilibrium. By comparing Q to K, the direction in which the system will move to achieve equilibrium can be determined. The equilibrium constant can be used to calculate the partial pressures at equilibrium. Changes to external conditions can disturb equilibrium by adding or removing gaseous reactants or products, compressing or expanding the system, and changing temperature.

Applying Eel Chatterer's principle, the direction of an equilibrium shift can be inferred when changes in concentration, pressure, or temperature are made. If a gaseous species is added, the reaction will proceed to consume it, while removal of a gaseous species will cause the system to restore that species. Adding or removing a pure

liquid or solid has no effect on equilibrium. To shift the position of an equilibrium, a species must appear in the expression for K. When total pressure is increased by compression, the reaction occurs in the direction that reduces the number of gas moles, whereas a decrease in pressure due to expansion causes a shift in the opposite direction to increase gas moles.