Chapter 16: Chemical Equilibrium

See Appendix III Common Mathematical Operations in Chemistry 

Part B. Logarithms

Part C. Quadratic Equations

Determine the correct number of significant figures when using logs and exponents. (*See p. 668)

DEFINE:

• Dynamic equilibrium
• Equilibrium constant (K)
• Reaction quotient (Q)
• The mathematical relationships between chemical equations and K (reaction is reversed or multiplied by a constant, two or more reactions are combined)
• Le Chatelier’s Principle

DO:

• Write an expression for the equilibrium constant (K) from a balanced chemical reaction (Law of Mass Action)
• Explain the meaning of K>>1, K>1, K=1, K<1 and K<<1  (*See 19.9 p.797-8 for K>1, K<1)
• Express K for gas phase reactions in terms of pressure (K_p) or concentration (K_c) and use the ideal gas law to convert between them
• Explain why K is a unitless number and why pure solids and liquids do not appear in expressions for K
• Explain why when ΔG=0 the system is at equilibrium (*See 19.8)
• Use Le Chatelier’s Principle to predict the effect of changing the concentration of reactants or products (through their addition or removal), volume, pressure, and temperature (when it is known if the reaction is exothermic or endothermic) on a system at equilibrium

CALCULATE:

• K from equilibrium concentrations
• K at temperatures other than 25°C from ΔH°_rxn and T (two point equation). (*See p. 799-800) 
• Write and compute entries for ICE tables used to analyze equilibrium reactions
• Write an expression for the reaction quotient (Q) and calculate a value for Q based on initial concentrations of reactants and products
• Compare Q to K to determine whether the reaction will proceed in the forward (Q<K) or reverse (Q>K) direction to reach equilibrium or is already at equilibrium (Q=K).  Explain why this comparison works
• Use Q to calculate free energy ΔG for non standard conditions (ΔG = ΔG° + RTlnQ) (*See 19.8)
• Calculate the equilibrium constant K from ΔG° and visa-versa (*See 19.9)
• Use ICE tables to set up algebraic expressions to calculate equilibrium concentrations from K and initial concentrations of reactants and products
• Determine when it is appropriate to make simplifying assumptions (5% rule) to solve equilibrium calculations and when exact solutions are required (for example the quadratic equation is required)
• Write out and solve the quadratic equation for a given ICE table.

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