Chemical Equilibrium Flashcards
What is dynamic equilibrium?
The condition where the rate of the forward reaction equals the rate of the reverse reaction
Are the concentrations of reactions and products equal at equilibrium?
No the rate is
What is the formula for the equilibrium constant?
aA + bB —> cC + dD
K= [C]^c[D]^d/[A]^a[B]^b
Concentration of products raised to coefficient in balanced equation divided by concentration of reactants raised to coeffficient
What is true of the equilibrium constant?
Applies to system at equilibrium, ratio of products to reactants, concentration is raised to equivalent stoichiometric coefficient
What is the law of mass action?
Relationship between a balanced chemical equation and K
How can you express K?
Kc (concentration)
Kp (pressure)
How can you relate Kc and Kp?
Kc= Kp(1/RT)^deltan
Kp= Kc(RT)^deltan
What is delta n?
Change in moles from products to reactant
Find the stoichiometric difference of gases
For what value does Kc equal Kp?
Delta n is 0
What is activity?
A measure of deviation from the standard state
What is a large K indicate?
K > 1
Numerator is greater than denominator so the amount of products is favored over reactants
Reaction lies to the right
What does a small K indicate?
K < 1
Numerator smaller than denominator so the amount of reactants is favoured over reactants
reaction lies to the left
What does a K that is approx 1 mean?
neither direction is favoured
reaction proceeds about halfway to completion
If you reverse a chemical equation how can you find the equilibrium constant given K of the reaction before it was reversed?
1 divided by the equilibrium constant of the reaction before it was reversed
If you multiply an equation by “n” hpw does the original K change?
raise every concentration to “n”
multiply K by “n”
If you are adding together two equations to get the final equation, how can you find the K values given K of the original?
multiply them together
What are ICE tables used for? What does ICE stand for?
to find the equilibrium concentration in order to find K
Initial, change, equilibrium
What is Q?
the reaction quotient
measures the relative amounts of products and reactants present during a reaction at a particular point in time (measures progress towards equilibrium)
What does the reaction quotient do?
predicts the direction of change (if we know K)
always approaches equilibirum as the final state
What does it mean if Q < K?
reaction proceeds to the right, products need to be formed to reach equilibrium
What does it mean if Q > K?
reaction proceeds to the left, reactants need to be formed to reach equilibrium
What does it mean if Q = K?
equilibrium has been reached
How can you find the equilibrium amounts when you know K and all but one amount of reactant/product?
- write the expression for K
- rearrange formula to isolate unknown
- plug in values and solve
How can you find the equilibrium amounts when you know K and all of the initial amounts?
- using balanced chemical equations, create an ICE table
- use initial amounts to calculate Q and figure out the direction the reaction will proceed
- for the C row, represent the change with x, + or - depending on direction, and include coefficients
- add up columns to get E row
- sub into K formula and solve
How can you simplify equilibrium problems?
careful inspection of K and initial amounts
a large amount of initial reactant and a small K can mean that the equilibrium concentration may be essentially unchanged
What is Le Chatelier principle?
When a chemical system at equilibrium is disturbed, the system shifts in a direction that minimizes the disturbance.
How can you disturb a chemical system at equilibrium?
- change the amount of product
- change the amount of reactant
- change the reaction volume
- change the reaction pressure
- change the reaction temperature
What is true when add/remove reactant?
increasing the amount of reactant (Q<K) causes a shift to the right
Decreasing the amount of reactant (Q>K) causes a
shift to the left
What true when you add/remove product?
Increasing the amount of product (Q>K) causes a shift to the left
Decreasing the amount of product (Q<K) causes a shift to the right
What is true when you increase/decrease the volume?
Increasing the volume causes a shift in the direction that has more moles of gas
Decreasing the volume causes a shift in the direction that has fewer moles of gas
What is true when you increase/decrease the pressure?
Increasing the pressure causes a shift in the direction that has fewer moles of gas
Decreasing the pressure causes a shift in the direction that has more moles of gas
What is true when you increase/decrease the temperature for exothermic reactions?
Increasing the temperature causes exothermic reactions to shift left and decreases K
Decreasing the temperature causes exothermic reactions to to shift right and increases K
What is true when you increase/decrease the temperature for endothermic reactions?
Increasing the temperature causes endothermic reactions to shift right and increases K
Decreasing the temperature causes endothermic reactions to shift left and decreases K
