Honors Chemistry Unit 11 Equilibrium

Equilibrium

condition where the forward and reverse reactions in a system occur at the same rate

Equilibrium occurs in a…

• dynamic state

• closed system

forward and reverse reactions still happen

In an equilibrium, both

put a lid on it

To create an equilibrium in a flask,

Concentrations at Equilibrium

• products and reactants property will not be equal at equilibrium

• amount of P and R will remain constant

• rates are equal, concentrations are constant(RECC)

Phase Equilibrium

• equilibrium that exists during a change of state

• Rf = Rm

Solution Equilibrium

• solids that are dissolved in liquids can exist in an equilibrium

  • only in saturated solution

Chemical Equilibrium

• in a closed system, a reversible reaction will eventually reach equilibrium

Equilibrium Constant

Keq = [products]/[reactants]

• tell us whether there are more reactants or products at equilibrium

• only a change in temperature will change Keq

How Equilibrium Constant Affects Properties

• when products>reactants, Keq>1

  • the larger the K the more products

• when products<reactants, Keq<1

  • the smaller the K the less products

• used for comparing solubility or strength of acids

  • a large K value means a strong acid

  • a small K value means less soluble

Le Chatalier’s Principle

• when a system at equilibrium is placed under a stress, the system will undergo a change as to relieve that stress and restore a state of new equilibrium

• helps predict change

  • which direction will it shift

  • which reaction is formed

  • new concentrations at equilibrium(increase or decrease)

Stresses that can be Applied with Le Chatalier’s Principle

• temperature change

• concentration change

• pressure change

• catalyst(don’t affect equilibrium, speeds up reaction)

Le Chatalier’s In Action

• when you take something away from a system at equilibrium, the system shifts in such a way to replace some of what you took away

• when you add something to a system at equilibrium, the system shifts in such a way to use some of what you’ve added

• Add = move away

• Take Away = move towards

• concentrations increase in the direction you shift towards

Pressure with Le Chatalier’s Principle

• only affects gases

• increase in pressure means more moles

• decrease in pressure means shift to side with less moles

C. 1×10^-1

Which equilibrium constant indicates the highest concentration of product?

A. 2×10^-2

B. 4×10^-4

C. 1×10^-1

D. 3×10^-3

A. dynamic phase equilibrium

Which type of equilibirum exists in a sealed flask containing Br(l) and Br2(g) at 298K and 1atm?

A. dynamic phase equilibrium

B. static phase equilibrium

C. static solution equilibrium

D. dynamic solution equilibrium

A. the concentration decreases

Given the reaction at equilibrium:

2NO2(g) < - > N2O4(g) + 55.3 kJ

What happens to the concentration of N2O4(g) if the concentration of NO2(g) is decreased?

A. the concentration decreases

B. the concentration increases

C. the concentration remains the same

A. shift right

Given the reaction at equilibrium:

2NO2(g) < - > N2O4(g) + 55.3 kJ

In which direction will the equilibrium shift if the pressure is increased?

A. shift right

B. no shift

C. shift left

A. decrease

Given the reaction at equilibrium:

N2(g) + O2(g) < - > 2NO(g)

As the concentration of N2(g) increases, the concentration of O2(g) will

A. decrease

B. increase

C. remain the same

C. increasing the temperature

Given the reaction at equilibrium:

N2(g) + 3H2(g) < - > 2H3(g) + 22kcal

Which stress would cause the equilibrium to shift to the left?

A. adding H2(g) to the system

B. adding N2(g) to the system

C. increasing the temperature

D. increasing the pressure

A. an increase in pressure

In the equilibrium reaction:

A(g) + 2B(g) + heat < - > AB2(g)

the rate of the forward reaction will increase if there is

A. an increase in pressure

B. a decrease in the concentration of A(g)

C. an increase in the volume of the reaction vessel

D. a decrease in temperature