# Chemical Equilibrium–Study Guide

#### Learning Objectives and Key Terms

Key Terms and ideas you should know

• Law of mass action
• Dynamic equilibrium
• Homogenous equilibrium with examples
• Write equilibrium constant expressions for the equations provided
• Heterogeneous equilibrium and examples
• Write equilibrium constant expressions for heterogeneous equilibria
• Difference between concentration quotient and equilibrium constant Qc Vs Kc
• Factors affecting chemical equilibrium: need to elaborate each
• Concentration
• Change in Pressure / Volume for gaseous reactants
• Temperature
• Addition of an inert gas
• Le Chatliers principle definition
• Predicting shift in equilibrium based on the variation of concentration, temperature, pressure / volume change all possible combinations. One example for each type of shift like
• Removing a reactant
• Removing a product
• Adding heat to an exothermic / endothermic reaction
• Taking away heat from an exothermic / endothermic reaction
• Adding an inert gas without change in volume / with change in volume
• Values of Kc and its implication
• What does it mean if the value of Keq is very large / very small / = 1
• What will the value of Kc be if the reaction is reversed
• What happens to the value of Kc if the equation is multiplied by a coefficient
• Relation between Kc and Kp
• Problems
• Determining molar concentrations of reactants and products
• Generate an ICE table to calculate equilibrium concentrations
• Determine value of Kc form equilibrium concentrations
• Find the equilibrium concentration if the equilibrium constant is given
• Find the equilibrium concentration of one of the reactants in a reaction when the equilibrium expression is a perfect square.
• Find the equilibrium concentration when the equilibrium constant is given and the equilibrium expression is NOT a perfect square; you will use the quadratic equation.
• Determine the new equilibrium concentrations of reactants when a stress is applied by adding a known quantity of reactant. Problems on Le Chatliers Principle.
• Predicting the quantity of a reactant needed to obtain a known increase in the concentration of one of the products. Le Chatliers principle.
• Predicting concentrations of reactants or products when Kc is known and the value of Kc is small – using the 100th rule.
• Problems converting Kc to Kp and Vice Versa

#### Spontaneity of Chemical Reactions

• Define spontaneity
• Define Entropy
• Predicting entropy of chemical reactions using states of matter, number of entities and temperature changes.
• Significance of free energy
• Predicting spontaneity based on values of free energy
• When free energy or $\Delta$G = O
• When free energy or $\Delta$G = < O or negative
• When free energy or $\Delta$G = > O or positive
• Relationship between $\Delta$G and equilibrium constant $\Delta$G = -RTlnKc or $\Delta$G = -RTln Kp, ln can be changed to log but multiply by 2.303 appropriately
• Gibbs-Helmholtz equation$\Delta$G = $\Delta$H -T$\Delta$S
• Predicting spontaneity based on values provided
• Why can’t Kc have a negative value?
• What is the effect of the presence of a catalyst on equilibrium constant?
• Predict the temperature at which a reaction would become spontaneous. Using Gibbs-Helmholtz equation, assumption is that the system is at equilibrium, then calculate the temperature ‘T’