14A - Equilibrium and The Equilibrium Constant

Question 1

Theory: Chemical Reactions can go in ___ directions.

Answer 1

Both.

Question 2

Def: What is Dynamic Equilibrium? What happens to concentrations/partial pressures at this state.

Answer 2

Dynamic Equilibrium occurs when fwd rate and rvs rate of rxn are equal.
No more change in concentration occurs over time.

Question 3

Def: What is a reversible reaction?

Answer 3

A reaction that can proceed both forward and backwards.

Question 4

Def: What is the position of equilibrium?

Answer 4

An indication of the relative amounts of reactants and products present in a rxn mixture at eqm.

Question 5

Theory: What is mean when the eqm position is to the right? Left?

Answer 5

Right: Amount of product&raquo_space; amount of reactant.
Left: Amount of reactant > amount of product.

Question 6

Theory: What are the three types of rxn arrows, and the rates of rxn associated with them.

Answer 6

For reactants A and products B,
1. Double arrow: Generic eqm
kf[A] = kr[B]
2. Single arrow to the right: Fwd rxn
kf[A]
3. Single arrow the left: Rvs rxn
kr[B]

Question 7

Theory: Are concentrations of products and reactants equal at eqm?

Answer 7

No.

Question 8

Theory: What is the relationship btw products and reactants concentrations at eqm? What constant does this produce.

Answer 8

[B]/[A] = kf / kr = Keq
The eqm constant.

Question 9

Def: What are the two directional rate constant?

Answer 9

kf = fwd
kr = rvs

Question 10

Theory: Eqm changes with ___, and not ___.

Answer 10

Temp.
Concentration.

Question 11

Def: What is the concentration-based eqm constant, Kc, for the following reaction:
aA + bB <-> cC + dD?

Answer 11

Kc = [C]^c [D]^d / [A]^a [B]^b = keq
Concentrations at eqm.
Keq is prod over reactants.

Question 12

Theory: What does the value of Keq signify?

Answer 12

Keq > 1, Product side favored
1 > Keq > 0, neither side favored
Keq < 0, Reactant side favored

Question 13

Theory: What unit is Keq?

Answer 13

Unitless.

Question 14

Def: What are the three eqm constants?

Answer 14

Keq = generic eqm
Kc = concentration-based
Kp = pressure-based

Question 15

Def: What is Kp? How is it found and why? What unit is pressure usually in for these calculations.

Answer 15

Pressure based eqm constant.
The concentration of a gas is proportional to it’s partial pressure, therefore the partial pressures can be used instead of concentrations.
Bar.

Question 16

Theory: What happens to Keq when the rxn is reversed.

Answer 16

Keq is inverted.

Question 17

Theory: What happens to Keq when the rxn is multiplied by some coefficient, n.

Answer 17

All stoich coefficients are multiplied by n, so all exponents in the Keq eqx are multiplied by n.
Therefore, Keq can be raised to the power of n.

Question 18

Theory: In for example, a multi-step rxn, what happens to Keq if two chemical equilibrium eqx are combined.

Answer 18

Keq of each step will be multiplied with each other.

Question 19

Theory: What is the relationship between Kc and Kp?

Answer 19

Because n/V = P/RT, and n/V is the molarity at Pressure P for an ideal gas, we can rewrite Kp for the gas in these terms. After simplifying.
Kp = Kc (RT)^(Change in n)
Change in moles is difference between mole of gas products and gas reactants in the stoich eqx.

Question 20

Theory: What happens to pure solid or liquids in Keq? Are they relevant to eqm and why?

Answer 20

Ignored, set to 1.
They are relevant, and necessary for some eqm eqx. They must exist in solid/phase while the rxn is in eqm, but will not affect Keq.