Chemistry: Atoms First 2e

# Summary

## 13.1Chemical Equilibria

A reversible reaction is at equilibrium when the forward and reverse processes occur at equal rates. Chemical equilibria are dynamic processes characterized by constant amounts of reactant and product species.

## 13.2Equilibrium Constants

The composition of a reaction mixture may be represented by a mathematical function known as the reaction quotient, Q. For a reaction at equilibrium, the composition is constant, and Q is called the equilibrium constant, K.

A homogeneous equilibrium is an equilibrium in which all components are in the same phase. A heterogeneous equilibrium is an equilibrium in which components are in two or more phases.

## 13.3Shifting Equilibria: Le ChĂ˘telierâ€™s Principle

Systems at equilibrium can be disturbed by changes to temperature, concentration, and, in some cases, volume and pressure. The systemâ€™s response to these disturbances is described by Le ChĂ˘telierâ€™s principle: An equilibrium system subjected to a disturbance will shift in a way that counters the disturbance and re-establishes equilibrium. A catalyst will increase the rate of both the forward and reverse reactions of a reversible process, increasing the rate at which equilibrium is reached but not altering the equilibrium mixtureâ€™s composition (K does not change).

## 13.4Equilibrium Calculations

Calculating values for equilibrium constants and/or equilibrium concentrations is of practical benefit to many applications. A mathematical strategy that uses initial concentrations, changes in concentrations, and equilibrium concentrations (and goes by the acronym ICE) is useful for several types of equilibrium calculations. We also learned that a negative value for Î”G indicates a spontaneous process; a positive Î”G indicates a nonspontaneous process; and a Î”G of zero indicates that the system is at equilibrium. We also saw how free energy, spontaneity, and equilibrium relate.

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