Equilibrium

Chapter 8. Chemical and Physical Change: Energy, Rate, and Equilibrium

Reversible Rxns and Chem Equilibrium

Up to now we have worked problems assuming that reactants are totally converted to products as

H₂ + I₂ g 2HI

If 4 moles of H₂ reacts get 8 moles of HI, etc.

"Many rxns can occur in..."

Many rxns can occur in the reverse direction (products to reactants) as well as in the forward direction (reactants to products).

In a closed system for A(g) g B(g)

at some point in time

"At this point it appears"

At this point it appears

Equilibrium is a ________________; on the molecular level the rxns continue but every time an A forms a B, a B turns into an A and the concs of A and B seem

"A(g)"

A(g) g B(g)

B(g) g A(g)

At equilibrium the

So

Law of Mass Action

or how to write an equilibrium constant expression.

aA(g) + bB(g)DcC(g) + dD(g)

[A] means that conc of A is in moles/L

"K_eq is equal to the..."

K_eq is equal to the product of the conc of the products raised to their stoichiometric coefficients divided by the product of the concs of the reactants raised to their stoichiometric coefficients.

The value of K_eq is

determined

Write equilibrium constant expressions for

2NO(g) + O₂(g) D 2NO₂(g)

2NH₃(g) D N₂(g) + 3H₂(g)

3O₂(g) D2O₃(g)

2NO₂(g) +7H₂(g) D2NH₃(g) + 4H₂O(g)

Heterogeneous equilibria

So far all examples have been for all species in the gas phase: homogeneous equilibria

Now for 2HgO(s) D 2Hg(l) + O₂(g) heterogeneous equilibrium

Write K_eq for

P₄(g) + 5O₂(g) D P₄O₁₀(s)

CaCO₃(s) D CaO(s) + CO₂(g)

CH₃COOH(aq) + H₂O(l) D CH₃COO^-(aq) + H⁺(aq)

Size of K: A(g) D B(g)

K>100 mainly have B at equilibrium, very little A; rxn is essentially complete

K<0.01 mainly have A at equil., very little B; essentially no rxn has occurred

K btn 1 and 100 more B than A at equil but have measureable amts of A and B

K btn 0.01 and 1 have more A than B at equil but have measurable amts of A and B

"Predict whether reactants or products..."

Predict whether reactants or products are favored at equil

S₂(g) + 2H₂(g) D 2H₂S(g) K=2.8x10^-21

CO(g) + 2H₂(g) DCH₃OH(g) K= 10.5

Br₂(g) + Cl₂(g) D2BrCl(g) K =58.0

I₂(g) D 2I(g) K = 6.8x10^-3

"Fluorine can react with oxygen..."

Fluorine can react with oxygen to yield oxygen difluoride: 2F₂(g) + O₂(g) D 2OF₂(g)

What is the value of K_eq if the following concentrations are found at equilibrium? [O₂] = 0.200mol/L; [F₂]=0.0100mol/L [OF₂]=0.0633mol/L

What is [O₂] at equil when [OF₂]=0.22mol/L and [F₂]=0.0300mol/L?

What is [OF₂] at equil when [F₂]=0.080mol/L and [O₂] = 0.650mol/L?

Le Chatelier’s Principle: the effect of changing conditions on equilbria

Le Chatelier’s Principle: when a stress is applied to a system at equil (which removes the system from equil) the system shifts to relieve the stress and reach a new equil state.

"Stresses are:"

Stresses are:

1. addition or removal of reactants and products at constant volume

"2."

2. changes in pressure : pressure is caused by gas molecules hitting the container walls.

If you increase the pressure, the rxn will shift

If you decrease the pressure,

"If you have the same..."

If you have the same no of gas molecules on both sides of the rxn,

"3."

3. Temperature changes (remember the value of K changes when you change the temp)

exothermic

endothermic

"4."

4. adding a catalyst: a catalyst

"Cl₂(g)"

Cl₂(g) + H₂(g) D 2HCl(g)

K = 2.6 x 10³³ and DH = -44kcal at 25^oC

Is the rxn endo or exothermic?

Are the reactants or products favored at equil?

What happens when:

increase pressure

inc conc of HCl

inc conc of Cl₂

dec conc of H₂

add a catalyst.

"7.59 Predict what happens when..."

7.59 Predict what happens when increase the pressure:

C(s) + H₂O(g) D CO(g) + H₂(g)

2H₂(g) + O₂(g)D 2H₂O(g)

2Fe(s) + 3H₂O(g) D Fe₂O₃(s) + 3H₂(g)

"7.61 The rxn 3O₂(g)"

7.61 The rxn 3O₂(g) D 2O₃(g) has DH=68kcal. Does the equil constant for the rxn increase or decrease when the temp increases?

"NH₃(g)"

NH₃(g) + O₂(g) D NO(g) + H₂O(g) +heat

Balance

Explain the effect on equil of

raising the pressure

adding NO(g)

decreasing the conc of NH₃

lowering the temp

adding a catalyst


	Chapter 8. Chemical and Physical Change: Energy, Rate, and Equilibrium


	Up to now we have worked problems assuming that reactants are totally converted to products as
	H₂ + I₂ g 2HI
	If 4 moles of H₂ reacts get 8 moles of HI, etc.


	Many rxns can occur in the reverse direction (products to reactants) as well as in the forward direction (reactants to products).
	In a closed system for A(g) g B(g)
	at some point in time


	At this point it appears




	Equilibrium is a ________________; on the molecular level the rxns continue but every time an A forms a B, a B turns into an A and the concs of A and B seem


	or how to write an equilibrium constant expression.
	aA(g) + bB(g)DcC(g) + dD(g)




	[A] means that conc of A is in moles/L


	K_eq is equal to the product of the conc of the products raised to their stoichiometric coefficients divided by the product of the concs of the reactants raised to their stoichiometric coefficients.
	The value of K_eq is
	determined


	2NO(g) + O₂(g) D 2NO₂(g)

	2NH₃(g) D N₂(g) + 3H₂(g)

	3O₂(g) D2O₃(g)

	2NO₂(g) +7H₂(g) D2NH₃(g) + 4H₂O(g)


	So far all examples have been for all species in the gas phase: homogeneous equilibria
	Now for 2HgO(s) D 2Hg(l) + O₂(g) heterogeneous equilibrium


	P₄(g) + 5O₂(g) D P₄O₁₀(s)

	CaCO₃(s) D CaO(s) + CO₂(g)

	CH₃COOH(aq) + H₂O(l) D CH₃COO^-(aq) + H⁺(aq)


	K>100 mainly have B at equilibrium, very little A; rxn is essentially complete
	K<0.01 mainly have A at equil., very little B; essentially no rxn has occurred
	K btn 1 and 100 more B than A at equil but have measureable amts of A and B
	K btn 0.01 and 1 have more A than B at equil but have measurable amts of A and B


	Predict whether reactants or products are favored at equil
	S₂(g) + 2H₂(g) D 2H₂S(g) K=2.8x10^-21
	CO(g) + 2H₂(g) DCH₃OH(g) K= 10.5
	Br₂(g) + Cl₂(g) D2BrCl(g) K =58.0
	I₂(g) D 2I(g) K = 6.8x10^-3


	Fluorine can react with oxygen to yield oxygen difluoride: 2F₂(g) + O₂(g) D 2OF₂(g)
	What is the value of K_eq if the following concentrations are found at equilibrium? [O₂] = 0.200mol/L; [F₂]=0.0100mol/L [OF₂]=0.0633mol/L

	What is [O₂] at equil when [OF₂]=0.22mol/L and [F₂]=0.0300mol/L?

	What is [OF₂] at equil when [F₂]=0.080mol/L and [O₂] = 0.650mol/L?


	Le Chatelier’s Principle: when a stress is applied to a system at equil (which removes the system from equil) the system shifts to relieve the stress and reach a new equil state.


	Stresses are:
	1. addition or removal of reactants and products at constant volume


	2. changes in pressure : pressure is caused by gas molecules hitting the container walls.

	If you increase the pressure, the rxn will shift

	If you decrease the pressure,


	If you have the same no of gas molecules on both sides of the rxn,


	3. Temperature changes (remember the value of K changes when you change the temp)
	exothermic
	endothermic


	Cl₂(g) + H₂(g) D 2HCl(g)
	K = 2.6 x 10³³ and DH = -44kcal at 25^oC
	Is the rxn endo or exothermic?
	Are the reactants or products favored at equil?
	What happens when:
	increase pressure
	inc conc of HCl
	inc conc of Cl₂
	dec conc of H₂
	add a catalyst.


	7.59 Predict what happens when increase the pressure:
	C(s) + H₂O(g) D CO(g) + H₂(g)
	2H₂(g) + O₂(g)D 2H₂O(g)
	2Fe(s) + 3H₂O(g) D Fe₂O₃(s) + 3H₂(g)


	7.61 The rxn 3O₂(g) D 2O₃(g) has DH=68kcal. Does the equil constant for the rxn increase or decrease when the temp increases?


	NH₃(g) + O₂(g) D NO(g) + H₂O(g) +heat
	Balance
	Explain the effect on equil of
	raising the pressure
	adding NO(g)
	decreasing the conc of NH₃
	lowering the temp
	adding a catalyst