Unit 3 - Equilibrium, Acids and Bases

Concentration [ ] vs Time will plot a straight line for a reaction of the

Zero Order

ln[ ] vs Time will plot a straight line for a reaction of the

First Order

1/[ ] vs Time will plot a straight line for a reaction of the

Second Order

What is an equilibrium reaction, and what happens to products and reactants when reached?

A reaction that is reversible, and the forward ad reverse rates become equal at equilibrium.

Are the concentrations of reactants and products at equilibrium always equal? Why or why not?

No, because equilibrium calls for equal RATES, not concentrations. If reactants and products react at the same rate, they are balanced; even if equilibrium concentrations differ.

What is the equilibrium expression?

K={\frac{{[C]^c[D]^d}}{[A]^{a}[B]^{b}}}

where:

• C and D = product concentrations

• A and B = reactants concentrations

• c, d, a, b = stoich coefficients

When can simplifying assumption be used?

if inital [ ] / k > 1000

How to check is x is valid in ICE table after using simplifying assumption

x / initial [ ] *100 < 5%

What is the Haber Process

1. Start w/ N₂ from air and H₂ natural gasses

2. Reacted in a reactor at 400 - 450ºC, 200 atm with iron catalyst

3. Products and reactants cooled, resulting in liquid ammonia- unreacted N₂ and H₂ gas recycled to be used again

The rxn 2 reactants → 1 product has a specific Kc. Find:

1. Kc for 4 reactants → 2 products

2. Kc for 1 product → 2 reactants

3. Kc for 2 product → 4 reactants

1. (Kc)² → [prdts]² / [rxts']⁴ = ([prdts] / [rxts']²)²

2. Kc^-1

3. (Kc^-1)² = Kc^-2

What is the difference between Q and K?

Q compares the ratio of products to reactants at any given time, while K compares this ratio at equilibrium.

• Can compare Q and K to find which direction system will favor

Kp and Kc equation

Kp = Kc(RT)^Δn

• R is 8.314

• Kp in kPa

Le Chatelier stresses

1. Adding/removing species

2. Changing temp

3. Changing pressure

4. Adding catalyst

Response if volume of rxn container increases

Favors side with more mols:

• ↑V, ↓P, all partial Ps decrease

• Side with more mols is slowed more relative to equilib due to exponents making more affected

• Rxn favors side w more mols to increase rate

Response if volume of rxn container decreases

Favors side w less mols:

• ↓V, ↑P, all partial Ps increase

• Side with less mols rate relatively slower, bc side w more mols rate increases much more due to exponents

• To catch up to equilib, rxn favors side w less mols

Response if inert gas is added at constant volume

No response.

• Inert gas in same volume ↑P, but all partial pressures remain same

• Therefore no affect on Q and stays at equilib

Response if inert gas added at constant pressure

Favors side w more mols:

• Volume changes to maintain pressure with added inert gas

• ↑V, all partial pressures decrease

• Side w more mols rate affected more (slower)

• Rxn favors side w more mols

According to Lewis theory, define acid and base

Lewis acid: Electron pair ACCEPTOR

Lewis base: Electron pair DONOR

What is an oxyacid?

Acid where acidic H is bonded to O, e.g. H3PO4

How do bond strength and polarity affect acid strength?

• Bond strength: More strong bonds with central atom = WEAKER acid, harder to peel H+ off

  • Smaller central atoms increase bond strength (more e^- overlap)

• Bond polarity: More polar H-X bond (x is electronegative element) = STRONGER acid, water molecules more attracted to more positive H⁺

  • Bonded atom and number of non-protonated oxygens pull e^- cloud away from H⁺

Percent ionization formula

[H₃O⁺]/[HA] * 100

How does dilution affect percent ionization

Increases percent ionization

• Diluting decreases all concentrations, and product rate is more affected

• LCP, system favours products (ions)

• ↑[A^-], ↑% ionization

Is the reverse or forward reaction favoured + why?

CH3​COOH+OH−⇌CH3​COO−+H2​O

• Ka(CH₃COOH) = 1.8×10⁻⁵

• Ka(H₂O) = 1.0×10⁻¹⁴

Forward, bc Ka(CH₃COOH) > Ka(H₂O) → products of forward rxn more favoured

Proof for autoionization of water

for any conjugate pair:

K_w = K_a * K_b

=\left(\frac{\left\lbrack H3O+\right\rbrack\left\lbrack A-\right\rbrack}{\left\lbrack HA\right\rbrack}\right)\left(\frac{\left\lbrack HA\right\rbrack\left\lbrack OH-\right\rbrack}{\left\lbrack A-\right\rbrack}\right)

= [H₃O⁺][OH^-] = K_w

Is this salt acidic or basic?

NH₄Cl

Break down into ions:

• NH₄⁺ is weak acid, Cl^- is extremely weak base

• NH₄⁺ can react with water, makes salt sol’n ACIDIC

What type of titration?

Strong acid-strong base

What type of titration?

Weak acid-strong base

What type of titration?

Weak base-strong acid

What type of titration?

weak acid-weak base