CHMA11H3 Lecture Notes - Lecture 4: Dynamic Equilibrium, Equilibrium Constant, Chemical Equation
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14 Jan 2019
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CHMA11 Lecture 4: Dynamic Equilibrium
- Dynamic Equilibrium: point in time when the forward and reverse reaction rates are
equal for a given reaction
o Reversible Reactions: reactions able to proceed in both the forward and reverse
directions
o Dynamic equilibrium is called Dynamic due to the fact that both the forward and
reverse reactions are still occurring
▪ They are occurring at the same rate
o No change in concentration in the products or reactants is seen once dynamic
equilibrium is reached
▪ The concentrations of products and reactants doesn’t have to be the
same
• Some reactions reach equilibrium after most of the reactant has
been consumed
o In these cases, equilibrium favors products
• Some reactions reach equilibrium after most of the product has
been consumed
o In these cases, equilibrium favors reactants
o Equilibrium constant (K): allows us to quantify the relative amounts of reactants
and products at equilibrium
▪ Denotes the relationship between reactant and product concentrations
at equilibrium
• For aA + bB -> cC + dD at equilibrium
o K = [(C)c x (D)d ] / [(A)a x (B)b ]
o Understanding K
▪ Big K value: in this case, equilibrium favors
products
▪ Small K value: in this case, equilibrium favors
reactants
▪ Therefore the expression for K for a reaction is defined as the ratio of the
concentrations of the products raised to their stoichiometric coefficients
divided by the concentrations of the reactants raided to their
stoichiometric coefficients
• Both sets of concentrations must be at equilibrium
▪ Relationships between K and chemical equations
• When the equation coefficients are multiplied by a factor, K is
raised to that factor
o Knew = (Koriginal)n
• When a reaction is written backwards, K in inversed
o Knew = 1/Koriginal