Equilibrium Flashcards
memorize bro (85 cards)
What is the imbalance that occurs between the forward and reverse reaction called?
Dynamic Equilibrium - Never fully becoming product, constantly moving back and forth
What is a Dynamic Equilibrium not mean?
The # of Reactant molecules = The # of Products Molecules
What is chemical equilibrium?
The conditions in which the concentration of all reactants and products eventually stop changing
For equilibrium to occur, what must happen?
Neither the reactants or products can leave the system so the direction of the chemical reaction is written is arbitrary
What are all the requirements of the system at equilibrium?
- System must be closed
- System must have constant temperature
- No change in macroscopic properties (no colour change, no emission of gas bubbles, no releasing of heat, etc.)
- Opposite reactions occur at the same time
- Equilibrium is attained by starting with either reactant or products
What are the three types of reactions?
- Reactants are favoured when % reactions is < 1%
- Products favoured when % of reaction is > 99% (the reaction appears to have gone to completion and is usually written as a one sided arrow)
- Reaction appears to be at equilibrium when the % of reactions is between 1%-99%
What is the equilibrium constant?
Used to relate the concentration of reactants and products in a mathematical and predictable way
What is the equilibrium constant expression?
K = Equilibrium constant
K = [Products]/[Reactants]
What is the generic reaction formula for the equilibrium constant?
aA+bB <- -> cC+dD
K = [C]^c [D]^d/[A]^a[B]^b
What are three things to remember when taking the generic reaction equilibrium constant?
- K depends on the way the equation is written
- Liquids and solids are not included into the equilibrium expression because their concentration is constant and has already been included to the equilibrium product constant
- K has a constant value at a given temperature, it does not depend on original concentration, volume of container or pressure
How does the Equilibrium constant expression relate to reaction rates?
k(f) = rate of the forward reaction
k(r) = rate of reverse reaction
At equilibrium k(f) = k(r)
Therefore, K = k(f)/k(r) and Keq (forward) = 1/Keq(reverse)
How does Temperature affect the Keq?
Changing the temperature favours either the forward or reverse reaction
This causes a shift in the Keq value, as well as a change in the [participants]
A new equilibrium will be reached with it’s own Keq value for the reaction at that temperature
At constant temperature, changing the equilibrium concentration does not affect Keq because the rate constants are not affected by the concentration changes
When the concentration of one of the participants is changed, the concentration of the others vary in such a way as to maintain a constant value for the Keq
What is the magnitude of Equilibrium Constants?
The magnitude of Keq is a measure of the extent to which a given reaction has or will take place
K»1: Equilibrium lies to the right; products are favoured
K«1: Equilibrium lies to left; reactants are favoured
K = 1: Half of the reactants have turned into products
How can you predict the direction of the reaction?
The reaction quotient, Q, is used to predict whether a system is at equilibrium
Reaction Quotient = Q = [PRODUCTS]/[REACTANTS]
Q = K → The system is at equilibrium
Q < K → in order to attain equilibrium, the reaction will move from left to right
Q > K → in order to attain equilibrium, the reaction will move from right to left
What is the hundred rule and why can we do it?
If you have a small K value the HUNDRED RULE can be used to approximate the concentration
Recall that as K«1, the reaction will hardly proceed in the direction of the products
That means that at this temperature, not too much reactant will be decomposed into the products.
We can assume that a the change in concentration is VERY SMALL (almost none) and insignificant
What is the Hundred rule and the 5% rule (Validations)?
Hundred rule: [Reactants]/K
If the resultant number is greater than 100, you can approximate the x value as zero
the assumption must be validated: Use 5% Rule
X/[Reactants]i
RULE: a difference of <5% justifies simplification
What is an Irreversible reaction?
This means the reactants turn into products, and the process cannot go backwards.
What is a reversible reaction?
Other chemical reactions are reversible.
This is where the products can turn back into the reactants under the right conditions.
What is Le Chatelier’s Principle?
Adding or removing a Reactant or Product
the addition of a reactant or product increases the concentration of said reactant/product
the equilibrium will shift in the direction that will consume the added component
Note: the addition of a pure solid or liquid does not cause a shift in equilibrium
How does a change in volume affect the reaction?
volume ↑ = pressure ↓
shift to the side with more moles of gas
How does adding gas affect the reaction?
adding an inert gas causes no shift in the equilibrium position as long as it doesn’t affect the concentration or partial pressure
Pressure depends on the number of gas molecules in the system.
How does temperature (in an exothermic reaction) affect the reaction?
Heat is like a product in an exothermic reaction because the reaction releases heat
If you add more heat, the system moves away from making even more heat
So the equilibrium shifts backwards towards the reactants
ΔH is (-)
How does the temperature (in an endothermic reaction) affect the reaction?
Heat is like a reactant in an endothermic reaction
This is because the reaction needs heat to make products
If you add morehear, it shifts the equilibrium to make more products
ΔH is (+)
How does a catalyst affect the reaction?
It helps the system reach equilibrium faster (since the reaction rates are increased) but does not change the equilibrium position
A catalyst speeds up both forward and reverse reactions equally. Why?
Because it lowers the activation energy by the same amount
