Name______Date______Period______

Equilibrium Notes

Ammonia Gas Production Equilibrium

N2(g)+ 3H2(g) 2NH3(g)

Not equal concentration totals, but the number of NH3 decomposition is equal to the number of NH3 creation.

Opposing processes are in balance:

Forward rate (right) equals backwards rate (left)

How much is actually produced given a reversible reaction at equilibrium is given by:

aA(g) +bB(g) cC(g) + dD(g)

Homogeneous Reactions: all the reactants and products are in the same physical state. When the state is gaseous when there is a pressure increase the equilibrium shifts towards the side (reactant or product) that has the fewest moles – more moles more volume at STP.

Factor which affects only heterogeneous reactions (more than one phase)

Surface area -when 2 different phases react, reaction can only take place on surface. As shown by the flask of ethanol shown . The rates of condensation equals that of evaporation. Keq =[C2H5OH]

- increase surface area by cutting solid into smaller pieces (liquids in smaller droplets)

If a substance is in liquid form assume concentration equals 1 because it is a pure substance, its concentration is constant at a given temperature. Also the same for solids which has a uniform density and thereby concentration remains constant. Thusly these are not included in equilibrium calculations.

- In general - reactants with solids are slow (except powdered)

- gaseous reactants are faster (but watch for diatomic bonds!)

- reactants in ionic solution. are fastest if no bonds to break

Example: Precipitation reaction Ag+(aq) + Cl-(aq)  AgCl (s)

(aqueous ions are mobile (unlike in a solid ) and more concentrated than molecules in a gas)

Equilibrium

  1. Definition: Rate of forward reaction = Rate of reverse reaction
  2. Writing Keq’s:

a) products in NUMERATOR,

reactants in DENOMINATOR

b) use [ ] around substances and include their phases

c) (+) signs separating substances in equation BECOME (x) signs

d) coefficients BECOME exponents

e) NO liquids or solids !!!!!! Only aqueous and gas

  1. Solving for Keq’s: put the ENTIRE numerator in ( )

and the ENTIRE denominator in ( )

  1. Interpreting the equilibrium constant
  • If the Keq= >1 then PRODUCTS are favored More products than reactants at equilibrium.
  • If Keq near one= significant amounts of both reactants and products
  • If Keq= <1 the reactants favored More reactants than products at equilibrium.

LeChatelier: If stressed, shift to relieve stress

1)[ ] as a stress; If increase [ ] of reactants then shift RIGHT to use them up

If decrease [ ] reactants shift LEFT to put them Back

Same idea for products

2)If temp increases shift AWAY from heat

If temp decreases shift TOWARD heat

3)Pressure: Only directly affects gases (indirectly it can affect [ ] of other substances)

If pressure increase shift to side with LESS moles of gases

If pressure decreases, shift to side with GREATER moles of gases

Equilibrium Practice Problems

For the reaction: SiH4(g) + O2(g) SiO2(g) + H2O(g)

a. Write the equilibrium equation:

c. What is the equilibrium constant

if [SiH4] = 0.45M; [O2] = 0.25M; [SiO2] = 0.15M; and [H2O] = 0.10M at equilibrium?

  1. Which direction would the reaction go and why? (Towards products or reactants?)

2A(g) + B(s) ↔ C(g)

1. For the reaction above, predict which way the reaction will shift: left, right, or none:

a. the concentration of B is increased ______

b. the amount of C is decreased ______

c. the amount of A is decreased ______

2. For the reaction below, what would speed up the reaction?

NH4+ + H2O ↔ NH3 + H3O+

a. the forward reaction

b. the reverse reaction

3. Define reversible reaction equilibrium:

4. An equilibrium shift to the right means:

a. more products are produced

b. more reactants are produced

c. nothing happens

5. Use this reaction for each of the following:

2NO2 (g) + O2 (g) ↔ 2NO3 (g)

a. Write the expression for the equilibriumconstant.

b. If gas concentrations are as follows, 2.10 M NO2, 1.75 M O2, and 1.00 M NO3, calculateKeq

c. Using Keq from part c, are the reactants or products favored?

d. Using Keq from part c, calculate [NO3] if [NO2] = [O2] = 4.3 x 10-6

POTENTIAL ENERGY diagrams

Endo: 1. graph ends high

2. A + B + heat  AB

3. H = (+)

Exo 1. graph ends low

2. A + B  AB + heat

3. H = (-)