Equilibrium Flashcards
(57 cards)
What happens to the concentrations of reactants and products at when they reach equilibrium?
The concentrations of the reactants and products become constant, even if they aren’t always equal. They stop changing and the reaction continuously and dynamically continues in both directions.
At chemical equilibrium, does the rate of reaction in the forward direction equal the rate of reaction in the reverse direction?
Yes
Does it matter what mixture of reactants and products equilibrium originates from?
No, chemical equilibrium can originate from a mixture of reactants and products or a pure reactants and pure products.
What is the equilibrium constant K a ratio of?
The concentrations (or partial pressures) or reactants and the concentrations (or partial pressures) of products at equilibrium. K = [products]^nu/[reactants]^nu, where nu is the stoichiometric coefficient.
What is the reaction quotient Q?
Q is a measure of the progression of a reversible reaction in non-equilibrium conditions. It is a ratio of concentrations or a ratio of partial pressures of reactants and products to the powers of their stoichiometry. Q = [products]^nu/[reactants]^nu, where nu is the stoichiometric coefficient.
How are Q or K (partial pressures) and Q or K (concentration) related?
Pressure = concentration * (RT)^(deltanu) where delta nu is the difference in stoichiometric coefficients
What happens when Q(c) > K(c)?
If Q > K then that means that products is greater than reactants. So the reaction goes towards reactants to establish equilibrium.
What happens when Q(c) < K(c)
If Q < K, then that means products is less than the reactants. So the reaction goes towards products to establish equilibrium.
What is activity when talking about equilibirum constant k?
Activity is the concentration or partial pressures as a ratio to respect with a standard reference state (pressure, temp)
When K < 1 at equilibrium
More reactants than products
When K ~ 1 at equilibrium
Similar amts of reactants and products
When K > 1 at equilibrium
More products than reactants
What phases are not included in the equilibrium constant expression?
Pure solids, liquids and solvents since their concentrations/activities are considered constant and equal to one.
What is the definition of Le Chatelier’s principle?
When a reaction mixture at equilibrium is disturbed to non-equilibrium concentrations, the concentrations will change to counteract the disturbance and re-establish equilibrium.
According to Le Chatelier, what happens to equilibrium when there is an increase in pressure?
The equilibrium shifts to the side with less molecules.
According to Le Chatelier, what happens to equilibrium when there is an decrease in pressure?
The equilibrium shifts to the side with more molecules.
What happens when the pressure is doubled?
The concentration is doubled as well.
What happens to the progress of a reaction when the pressure changes, but the number of moles of gas in the reactants and products are the same? (Or if there is no gas present)
There is no effect on the progress of a reaction.
Why is the change in temperature ‘pseudo le chatelier?’
Because it results in a new equilibrium value, not the same value.
What happens when a reaction at equilibrium is heated for an endothermic reaction? Hint: heat + reactants –> products
Increase in products, rate of reaction to products is faster so k increases.
What happens when a reaction at equilibrium is heated for an exothermic reaction? Hint: reactants –> products + heat
Increase in reactants, rate of reaction to reactants is faster so k decreases.
What is the equilibrium constant in the opposite direction?
The equilibrium constant in one direction is the inverse of that in the opposite direction. K’(c) = 1/K(c) or K’(p) = 1/K’(p)
What happens with the equilibrium when the reaction occurs in the presence of a catalyst?
A catalyst increases the rate of the reaction by making a lower-energy pathway available for both forward and reverse reactions, equilibrium is achieved quickly but there is no change in equilibrium position.
How do you calculate K when reactions are added together?
Multiply their respective K values together to get a new K value.
