Equilibrium

Question 1

Irreversible reactions

Answer 1

1)Reactions that only precede in one direction only
2) Maximum amount of product is determined by limiting reagent

Question 2

Only way to effect Keq

Answer 2

Change temperature!!!

Question 3

Reversible reactions

Answer 3

Reactions that can proceed in one of two ways:
1) Forward (toward products, “to the right”)
2) Backward (toward reactants, “to the left”)

Usually do not proceed to completion because products can react together to form products.

Question 4

Dynamic equilibrium

Answer 4

Forward and reverse reactions are still occurring but the concentrations of products and reactants remain constant.

Question 5

Static equilibrium

Answer 5

The reaction has stopped

no net change in the concentrations of the products
or reactants

Question 6

Law of mass action

Answer 6

If the system is at equilibrium at a constant temperature, then the following ratio is constant:

Question 7

Equilibrium constant
(explain 3 facts of equilibrium)
- gibbs, rate, entropy

Answer 7

At equilibrium:
1) Rate of forward/reverse rxn are equal
2) Gibbs free energy= 0
3) Entropy is at a maximum

Question 8

How does a catalyst effect Keq? (lower transition state of the forward and backward reactions)

Answer 8

Catalyst make the reaction go faster toward its equilibrium position but can’t change the position or alter the value of the Keq.

Question 9

At a constant temperature, Keq =

Answer 9

constant

Question 10

Alternative Keq names? (only for gases and aqueous solutions)

Answer 10

Kp = Equilibrium constant for gases
Kc = Equilibrium constant for concentration

Same equation/interchangeable

Question 11

Problem example
What is the expression for the equilibrium constant for the
following reaction?
3 H2 ( g) + N2 ( g) ⇋ 2 NH3 ( g)

Answer 11

Question 12

What molecules do you exclude from Equilibrium constant equations?

Answer 12

Pure Solids (s) or Pure Liquids (l) do not appear in the law of mass action.

Only gases and aqueous species.

Question 13

Equilibrium constant vs Rate constant

Answer 13

Equilibrium expressions: the exponents are equal to the coefficients in the balanced equation.

Rate laws: do not used coefficients, and exponents are determined by experimental results.

Question 14

Reaction Quotient, Q
(difference from Keq?)

Answer 14

A calculated value that relate the reactant and product concentrations at ANY given time during a reaction.

Q is used to check product/reactant ratio during, while Keq is the product/reactant ratio at equilibrium.

Question 15

Comparison of Q to Keq?

Answer 15

Comparison provides information about where a reaction is with respect to the equilibrium state.

Question 16

Q < Keq

Answer 16

Then the forward reaction has not yet reached equilibrium.

1) There is a greater concentration of reactants than at equilibrium
2) The forward rate of the reaction is increased to restore equilibrium

Question 17

Q=Keq

Answer 17

The reaction is at dynamic equilibrium:

1) The reactants and products are present in equilibrium proportions.
2) The forward and reverse rates of the reaction are equal.

Question 18

Q > Keq

Answer 18

Then the forward reaction has exceeded equilibrium:

1) There is a greater concentration of products than at equilibrium.
2) The reverse reaction is increased to restore equilibrium.

Question 19

Further moment once at equilibrium?

Answer 19

Once a reaction is at equilibrium, any further movement in the forward or reverse direction will be non-spontaneous.

Question 20

Le Chatlier’s Principle

Answer 20

States that if stress is applied to a system, the system shifts to relieve that stress.

Question 21

Le Chatlier’s Principle: Pressure

Answer 21

Increasing pressure on a gaseous system (decreasing its volume) will shift the reaction to the side with the fewer moles of gas. Decreasing pressure on a gaseous system (increasing its volume) will shift the reaction toward the side with the more moles of gas.

Question 22

Le Chatlier’s Principle: Temperature

Answer 22

Increasing temperature of an endothermic reaction or decreasing temperature of an exothermic reaction will shift the reaction to the right.

Decreasing the temperature of an endothermic reaction or increasing the temperature of an exothermic reaction will shift the reaction to the left.

Question 23

How to shift the following reaction to left and right:

A (aq) + 2 B (g) <—-> C (g) + heat

Answer 23

Question 24

Kinetic product (in comparison to thermodynamic products)

Answer 24

Higher in energy than thermodynamic products and can form in lower temperatures.

Sometimes referred to as “fast” products because they form more quickly under such conditions.

Question 25

Thermodynamic products

Answer 25

Lower in energy than kinetic products and therefore more stable.

Despite proceeding more slowly than kinetic pathways, the thermodynamic pathway is more spontaneous
(more negative delta G).

Question 26

If the equilibrium constant for a reaction written in one direction is Keq, the equilibrium constant for the reverse reaction is

Answer 26

1/Keq