GenChem2 Long Exam 2

equilibrium

is a state in which there are no observable changes as time goes by

equilibrium

it is achieved when the rate of the forward and reverse reactions are equal and the concentrations of the reactants and products remain constant

physical equilibrium

what type of equilibrium is H_2O (l) ←> H_2O (g)

what type of equilibrium is N_2O_4 (g) ←> 2NO_2 (g)

chemical equilibrium

K = ([C]^c[D]^d)/([A]^a[B]^b)

Law of Mass Action

law of mass action

for a reversible reaction at equilibrium and a constant temperature, a certain ratio of reactant and product concentration has a constant value K

right, products

if K is much greater than 1 K»1, the equilibrium will lie to the ___ and favor the ___

left, reactants

if the equilibrium constant is much smaller than 1 K«1, the equilibrium will lie to the ___ and favor the ___

True

True or False: Any number greater than 10 is considered to be much greater than 1, and any number less than 0.1 is much less than 1

homogeneous equilibrium

applies to reactions in which all reacting species are in the same phase

example: N2O4 (g) → 2NO2 (g)

Heterogeneous equilibrium

applies to reactions in which reactants and products are in different phases

example: CaCo3 (s) → CaO (s) + CO2 (g)

False, not

True or False: The concentrations of solids and pure liquids are included in the expression for the equilibrium constant.

Kc = ([E][F])/([A][B])

A + B → C + D (K’c)
C + D → E + F (K’’c)
= A + B → E + F (Kc)
if Kc = K’c x K’’c, what is Kc in terms of A, B, E and F?

product

If a reaction can be expressed as the sum of two or more reactions, the equilibrium constant for the overall reaction is given by the ___ of the equilibrium constants of the individual reactions

reciprocal

When the equation for a reversible reaction is written in the opposite direction, the equilibrium constant becomes the ____ of the original equilibrium constant

writing equilibrium constant expressions

1. the concentrations of the reacting species in the condensed phase are expressed in M. In the gaseous phase, the concentrations can be expressed in M or atm

2. The concentrations of pure solids, pure liquids, and solvents do not appear in the equilibrium constant expressions

3. The equilibrium constant is a dimensionless quantity

4. In quoting a value for the equilibrium constant, you must specify the balanced equation and the temperature

5. If a reaction can be expressed as a sum of two or more reactions, the equilibrium constant for the overall reaction is given by the product of the equilibrium constants of the individual reactions

rate_f = kf[A][B]²
rate_r = kr[AB2]

chemical kinetics and chemical equilibrium

A + 2B ←> AB2
what is rate_f and rate_r?

rate_f = rate_r

chemical kinetics and equilibrium
given A + 2B ←> AB2
rate_f = kf[A][B]²
rate_r = kr[AB2]
What is the equilibrium in terms of rate_f and rate_r?

kf/kr = Kc = [AB2]/([A][B]²)

kf[A][B]² = kr[AB2]
what is Kc?

reaction quotient Qc

it is calculated by substituting the initial concentrations of the reactants and products into the equilibrium constant Kc expression

left to right

if Qc < Kc system proceeds from ________ to reach equilibrium

equilibrium

if Qc = Kc the system is at ______

right to left

if Qc > Kc system proceeds from _________ to reach equilibrium

calculating equilibrium concentration

1. express the equilibrium concentrations of all species in terms of the initial concentrations and a single unknown x, which represents the change in concentration

2. write the equilibrium constant expression in terms of the equilibrium concentrations. knowing the value of the equilibrium constant, solve for x

3. having solved for x, calculate the equilibrium concentrations of all species

ICE (initial, change, equilibrium) method

we can analyze a given reaction from its initial stages to when it reaches equilibrium, e.g., only the reactants are present, using _______

external stress

is equal to the change in concentration, volume, pressure, or temperature that removes the system from equilibrium state

left

changes in concentration
change: increase concentration of products
shifts the equilibrium:

right

changes in concentration
change: decrease concentration of products
shifts the equilibrium:

right

changes in concentration
change: increase concentration of reactants
shifts the equilibrium:

left

changes in concentration
change: decrease concentration of reactants
shifts the equilibrium: