Using the reaction quotient to predict the effect of a change in concentration
For a reaction system at equilibrium, the reaction quotient Q is equal to K, the equilibrium constant. K is a number.
If aA + bB
cC + dD
The concentrations of the individual components of the equilibrium system may vary widely for different equilibrium systems, but when the reaction quotient is calculated using the sets of concentrations from the various equilibrium systems, it is equal to K.
The reaction quotient Q no longer equals K if
If the concentration of a product such [C] is increased
If aA + bB
cC + dDA, B, C and D are substances that are all dissolved (solutes) or are all gases
where a, b, c and d are coefficients in the balanced equation
Solids, liquids and catalysts do not appear in the expression.
where a, b, c and d are coefficients in the balanced equation
Solids, liquids and catalysts do not appear in the expression.
| Q = | [C]c[D]d | |
| [A]a[B]b |
The concentrations of the individual components of the equilibrium system may vary widely for different equilibrium systems, but when the reaction quotient is calculated using the sets of concentrations from the various equilibrium systems, it is equal to K.
The reaction quotient Q no longer equals K if
for a system at equilibrium (Q = K), the concentration of a substance appearing in the expression is changed.
If the concentration of a reactant such as [A] is increased Q < K because reactants are in the denominator of the expression.
Reaction occurs to a greater extent in the forward direction to consume A UNTIL Q equals K.
This results in a different equilibrium composition where
Reaction occurs to a greater extent in the forward direction to consume A UNTIL Q equals K.
This results in a different equilibrium composition where
[A] is higher because it has been added and not entirely consumed.
[C] and [D] are higher because they were produced in the faster reaction during the period in which equilibrium is restored.
[B] is lower because it is consumed in the faster reaction during the periodi in which equilibrium is restored.
[C] and [D] are higher because they were produced in the faster reaction during the period in which equilibrium is restored.
[B] is lower because it is consumed in the faster reaction during the periodi in which equilibrium is restored.
If the concentration of a product such [C] is increased
Q > K because products appear in the numerator of the expression.
Reaction in the reverse direction is faster, and added C is consumed until Q again equals K.
This results in a new equilibrium composition where
Reaction in the reverse direction is faster, and added C is consumed until Q again equals K.
This results in a new equilibrium composition where
[C] is higher because it was added to the system. Some, but not all, of it is consumed in the reaction which is faster during the periodic in which equilibrium is restored..
[A] and B] are higher because they are produced in the faster reaction occurring during the period in which equilibrium is restored.
[D] is lower because it is consumed in the reaction occurring to restore equilibrium..
[A] and B] are higher because they are produced in the faster reaction occurring during the period in which equilibrium is restored.
[D] is lower because it is consumed in the reaction occurring to restore equilibrium..