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Lecture 6

sbc 200 Lecture Notes - Lecture 6: Chemical EquilibriumPremium

2 pages27 viewsFall 2016

Course Code
sbc 200

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The Equilibrium State
All reactions are reversible and under suitable conditions will reach a state of
At equilibrium, the concentrations of products and reactants no longer change
because the rates of the forward and reverse reactions are equal.
Chemical equilibrium is a dynamic state
The Equilibrium Constant
K= Kforward/Kreverse
K and the extent of reaction
K reflects a particular ratio of product concentrations to reactant concentrations
for a reaction.
A small value for K indicates that the reaction yields little product before reaching
equilibrium. The reaction favors the reactants
A large value for K indicates that the reaction reaches equilibrium with very little
reactant remaining. The reaction favors the products.
The Reaction Quotient Q
Q = [C]^c[D]^d/ [A]^a[B]^b
gives the ratio of product concentrations to reactant concentrations at any point
in a reaction.
At equilibrium: Q = K
Forms of K and Q
For an overall reaction that is the sum of two more individual reactions:
Qoverall = Q1 x Q2 x Q3 x ….. And
Koverall = K1 x K2 x K3 x
Qc(rev)=1/ Qc(fwd) & Kc(rev)=1/ Kc(fwd)
K and Q for hetereogeneous equilibrium
A hetereogeneous equilibrium involves reactants and/ or products in different
Pure solids and liquids are omitted from the expression for Q or K
Determining the Direction of Reaction
The value of Q indicates the direction in which a reaction must proceed to reach
If Q < K, the products must increase and the reactant decrease; reactants →
products until equilibrium is reached.
If Q > K, the reactants must increase and the products decrease; products →
reactants until equilibrium is reached.
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