SCH4U - Unit 3 - Equilibrium and Acids & Bases

Chemical Equilibrium

• Chemical reactions can happen in both directions, but the speeds of each direction will depend on which one is favoured

• Reactions will occur in both directions until a specific equilibrium ratio is reached and maintained

  • Reactions and reverse reactions correlate inversely until they reach equilibrium

• K_eq - The ratio of products to reactants that a reaction at equilibrium will maintain, so that both the forward and reverse reaction occur at the same rate

  • K_{eq}=\frac{Products}{Reactants}

    • When K_eq is between zero and one, the reaction will create more reactants, and is non-spontaneous and endothermic

    • When K_eq is greater than one, the reaction will create more products, and is spontaneous and exothermic

  • If aA+bB\lrArr cC+dD, K_{eq}=\frac{\left\lbrack C\right\rbrack^{c}\left\lbrack D\right\rbrack^{d}}{\left\lbrack A\right\rbrack^{a}\left\lbrack B\right\rbrack^{b}}

  • Temperature can affect the equilibrium constant

• Reaction quotients can be set up the same way as K_eq, except it does not occur at equilibrium

  • aA+bB\lrArr cC+dD, Q=\frac{\left\lbrack C\right\rbrack^{c}\left\lbrack D\right\rbrack^{d}}{\left\lbrack A\right\rbrack^{a}\left\lbrack B\right\rbrack^{b}}

  • If Q is less than K_eq, it will make more products to raise the ratio (proceeding to the right)

  • If Q equals K_eq, it is at equilibrium

  • If Q is greater than K_eq, it will make more reactants to lower the ratio (proceeding to the left)

ICE Tables

• I is the initial concentration

• C is the change in concentration

  • If it is product-favoured, the change is positive (concentration increases)

  • If it is reactant-favoured, the change is negative (concentration decreases)

  • The change “x” for each compound should be multiplied by the coefficient in the original reaction

• E is the concentration at equilibrium

  • It is a sum of the initial concentration and the change

Pressure Equilibrium