Chemical Equilibrium Flashcards
(24 cards)
Characteristics of a Dynamic Equilibrium
- reversible system,
- forward and reverse reactions occur at the same rate
- concentrations of reactants and products do not change with time
- opposing reactions never cease to occur
or a reversible reaction at equilibrium and a constant temperature, a certain ratio of reactant and product concentrations has a constant value, K (the equilibrium constant).
mass action expression
is achieved when the rates of the forward and reverse reactions
are equal and the concentrations of the reactants and products remain constant.
chemical equilibrium
is a numerical value that characterizes the relationship between the concentrations of reactants and products in a system at chemical equilibrium.
equilibrium constant
instead of the equilibrium constant by substituting the initial concentrations into the equilibrium constant expression.
reaction quotient
The ratio of initial concentrations of products to reactants is too
small.
To reach equilibrium, reactants must be converted to prod-
ucts.
The system proceeds from left to right (consuming reactants,
forming products) to reach equilibrium.
Q < K
The initial concentrations are equilibrium concentrations. The system is at equilibrium.
Q = K
The ratio of initial concentrations of products to reactants is too
large.
To reach equilibrium, products must be converted to reactants.
The system proceeds from right to left (consuming products, forming reactants) to reach equilibrium
Q > K
states that if an external stress is applied to a system at equilibrium, the system adjusts in such a way that the stress is partially offset as the system reaches a new equilibrium position.
Le Châtelier’s principle
LCP
Increase in the concentration of a substance
AWAY from the substance
LCP
Decrease in the concentration of a substance
TOWARDS the substance
LCP
Increase the pressure of the system
Towards the FEWER number of moles
LCP
Decrease the pressure of the system
Towards the HIGHER number of moles
LCP
Increase the temperature of the system
favors ENDOTHERMIC reaction
LCP
Decrease the temperature of the system
favors EXOTHERMIC reaction
LCP
Addition of an inert gas
towards HIGHER moles of gas
LCP
Addition of a catalyst
No change/shift
Which of the following is true regarding the concentration of products, for a chemical reaction that is already at equilibrium, assuming no disruptions to the equilibrium?
a. The concentrations of products will not change because there are no more reactants.
b. The concentrations of products will not change because the limiting reagent is gone.
c. The concentrations of products will not change because the forward and reverse rates are equal.
d. The concentrations of products will change continually because of reversibility.
c. The concentrations of products will not change because the forward and reverse rates are equal.
If the reaction quotient Q has a larger value than the related equilibrium constant, K, __________
a. the reaction is at equilibrium.
b. the reaction is not at equilibrium, and will make more products at the expense of reactants.
c. the reaction is not at equilibrium, and will make more reactants at the expense of products.
d. the value of K will increase until it is equal to Q.
c. the reaction is not at equilibrium, and will make more reactants at the expense of products.
Which of the following occurs when reactants are removed from a chemical reaction in solution or the gas phase at
equilibrium?
a. Q increases, so the equilibrium shifts to produce more products.
b. Q increases, so the equilibrium shifts to produce more reactants.
c. Q decreases, so the equilibrium shifts to produce more products.
d. Q decreases, so the equilibrium shifts to produce more reactants.
c. Q decreases, so the equilibrium shifts to produce more products.
Increasing the temperature of an endothermic reaction results in __________
a. more products and fewer reactants.
b. more reactants and fewer products.
c. more reactants and products.
d. fewer reactants and products.
e. no change in the quantities of reactants and products.
a. more products and fewer reactants.
Given: 2A(g) B(g) + C(g) ∆H˚ = +27 kJ K = 3.2 x 10-4
Which of the following would be true if the temperature were increased from 25˚C to 100˚C?
1. The value of K would be smaller.
2. The concentration of A(g) would be increased.
3. The concentration of B(g) would increase.
a. 1 only
b. 2 only
c. 3 only
d. 1 and 2 only
e. 2 and 3 only
c. 3 only
Which of the listed perturbations will change the position of equilibrium for the following reaction? List those that do
as a sequence of letters, e.g., ACE. (There is more than one.)
NH4CO2NH2(s) 2NH3(g) + CO2(g)
A. Increasing the quantity of NH4CO2NH2(s)
B. Removing CO2(g)
C. Increasing the total pressure
D. Increasing the volume of the container
B. Removing CO2(g)
C. Increasing the total pressure
D. Increasing the volume of the container
PbCl2 has limited solubility in neutral water. But the amount of lead ions is reduced when sodium chloride is added to
the water. Addition of sodium chloride has no impact on the solubility of Ca(OH)2. Which statement explains why?
PbCl2(s) Pb2+(aq) + 2 Cl-
(aq) K=1.6 x 10-5
a. Sodium ions reacts with the lead ions that are produced.
b. Addition of sodium ions reduces the solubility of any slightly-soluble solid.
c. Adding sodium chloride effectively adds aqueous chloride ions. The addition of chloride ions has a LeChateliertype impact, drives the PbCl2 solubility to the left, and results in less PbCl2 dissolving.
c. Adding sodium chloride effectively adds aqueous chloride ions. The addition of chloride ions has a LeChateliertype impact, drives the PbCl2 solubility to the left, and results in less PbCl2 dissolving.
