8. Equilibrium Flashcards
Define equilibrium.
At equilibrium, the rate of the forward reaction is equal to the rate of the reverse reaction, and thus, no changes in concentration are observed (although forward and reverse reactions are constantly occurring).
What is the equilibrium constant? What is the equilibrium expression?
Keq = [products]^x / [reactants]^y
x and y are stoichiometric coefficients.
At a given temperature, any reaction will proceed towards its equilibrium concentrations of product and reactant. Using the above equation, we can find the equilibrium constant.
Pure liquids and solids are not included in the equilibrium expression because their concentrations cannot change. If have gases, we use partial pressures instead of concentrations.
t or f, the equilibrium constant changes with temperature.
true, therefore, Keq is only a constant for a given temperature.
Explain
K = 1
K > 1
K < 1
K = 1 indicates that [R] = [P] at equilibrium
K > 1 indicates that products are favored at equilibrium
K < 1 indicates that reactants are favored at equilibrium
t or f, Keq can be negative.
False, Keq can only be positive
concentrations cannot be negative
What is the reaction quotient (Q)?
At a given temperature, the [R] and [P] are governed by their Keq. However, in real world situations, the concentrations may be anything (i.e. not actually at equilibrium concentrations). The reaction quotient is the equilibrium expression using the given concentrations (not eq concentrations).
Explain
Q = K
Q > K
Q < K
Q = K, then the concentrations are at equilibrium.
Q > K, products are currently favored, and the reaction will shift to the left to find equilibrium.
Q < K, reactants are currently favored, and the reaction will shift to the right to find equilibrium
What is Le Chateliers principle?
The principle explains that a system at equilibrium will try to restore equilibrium if any changes are imposed on that system. The most common situation is adding or removing reactants or products.
If we add reactant, the system will want to consume that reactant to return to equilibrium concentrations (right shift).
N2 (g) + 3H2 (g) 2NH3 (g) + heat
Explain what happens if you decrease the volume this reaction takes place in.
Recall for gaseous reactions, we use partial pressures instead of []’s. If volume decreases, then pressure will increase. To help restore equilibrium, the reaction must shift to the side with LESS moles (to try reduce pressure).
N2 (g) + 3H2 (g) 2NH3 (g) + heat
So V decreases, P increases, the reaction will shift to the products. If volume increases, the opposite would occur to try maintain pressure.
N2 (g) + 3H2 (g) 2NH3 (g) + heat
Explain what happens if you increased the temperature of the reaction.
heat is written on the products side, thus, this reaction releases heat (exothermic). Similar to []’s, if we add heat (increase temperature), the reaction will shift to the left to try and restore equilibrium.
Note: unlike changing pressure or []’s, changing temperature will affect a reactions Keq.
t or f, Le Chateliers principle only applies to reactions that are already in equilibrium.
true! for example, all reactions proceed faster with increased temperature. For an exothermic reaction with no products formed, increased temperature will make the forward reaction go faster (collision theory). Once at equilibrium the increased T will encourage the reverse reaction.
What happens if you add an inert gas to a system that is held at constant pressure?
The added gas will cause volume to increase which effectively reduces the partial pressures of the system. If their partial pressures have been reduced, the system will shift to the side with more moles.
What happens if you add an inert gas to a system that is held at constant volume?
The added gas has no effect, unlike if you add an inert gas to a system that is held at constant pressure
How does a catalyst affect equilibrium?
A catalyst has no effect at equilibrium as it increases the forward and reverse reactions equally.
What is solvation? What is hydration?
When a solute is dissolved (dissolution) in a solvent. solvation is when the solvent fully surrounds the solute. When this occurs with water, it is hydration.
