Chapter 5B - Equilibrium Law
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What is the Equilibrium Law?
Relates the concentrations of reactants and products formed at equilibrium
What is K?
Ratio of the concentrations of the reactants to the concentrations of the products
What are the units for K?
Units will depends on the equilibrium expression.
What is the equilibrium constant?
• K is constant for an equilibrium mixture at a given temperature • Value of K can only be affected by change in temperature.
What is the equilibrium constant used for?
Indicating the extent of the reaction Note: does not indicate the rate of reaction K is only relevant to the equation exactly as its writtien
If K > 10⁴
• significant conversion of reactants into products by the time equilibrium is reached • large extent, significant concentration of products • position of equilibrium favours the forwards reaction
If K < 10-⁴
• little conversions of reactants into products by the time equilibrium is reached • small extent • significant proportion of reactants • position of equilibrium favours the reverse reaction
If 10-⁴ < K < 10⁴
• considerate concentrations of both reactants and products are present • moderate extent
What effect does doubling the coefficients of a reaction have on the equilibrium constant?
K is squared
What is the reaction quotient?
• When a system isn’t at equilibrium, the number calculated from equilibrium expression is Q • quantitative measure of extent that can be used at any stage of the reaction
What values can Q take?
Any positive or zero value (except that of K) at a given temperature
What does the value of Q indicate? In words
What is occurring inside the reaction vessel at a particular point in time
If Q = K
Reaction system is at equilibrium
If Q does not equal K
Reaction system is not at equilibrium
If Q > K
• Equilibrium position shifts to the left as more products exist than reactants, hence system wants to make more products. • net backwards reaction is occurring until enough reactants are made and Q = K
What does Net Backwards Reaction mean?
Rate of the backwards reaction is greater than the rate of the forwards reaction
If Q < K
• Equilibrium position shifts to the right • More reactants exist compared to products, hence system wants to make more products to get to equilibrium • net forwards reaction until enough products are made and Q = K
What does a Net Forwards reaction mean?
Rate of forward reaction is greater than rate of the backwards reaction