Equilibrium Basics
What does it mean when a chemical system is at equilibrium?
Forward and reverse reaction rates are equal; concentrations remain constant.
What happens to equilibrium if you add more reactants?
Shifts right (toward products).
What does RICE stand for in an RICE table?
Reaction, Initial, Change, Equilibrium.
What does Kc represent?
Equilibrium constant using molar concentrations.
What does Ksp stand for?
Solubility product constant — for slightly soluble salts.
True or False: At equilibrium, the amount of reactants and products must be equal.
False. Their rates are equal, not amounts.
What happens when pressure increases in: N₂ + 3H₂ ⇌ 2NH₃?
Shifts right — fewer gas moles on product side.
True or False: All reactions need x in RICE tables.
False — some reactions use given equilibrium concentrations directly.
How is Kp different from Kc?
Kp uses partial pressures of gases.
Write Ksp for BaSO₄ ⇌ Ba²⁺ + SO₄²⁻
Ksp = [Ba²⁺][SO₄²⁻]
Write the equilibrium expression for: N₂ + 3H₂ ⇌ 2NH₃
K = [NH₃]² / ([N₂][H₂]³)
A catalyst is added. What changes?
Increases rate, but does not affect equilibrium position.
Given initial: 1.0 M A, 0.0 M B. A ⇌ 2B, K = 4. Set up RICE.
I: 1.0
Write the Kp expression for: 2NO₂ ⇌ 2NO + O₂
Kp = (P_NO)²(P_O₂) / (P_NO₂)²
If Ksp = 1.1 × 10⁻¹⁰, is the salt very soluble?
No — low Ksp means low solubility.
Why are solids and liquids excluded from the equilibrium expression?
Their concentrations don’t change during the reaction.
In an exothermic reaction, what shift happens when temperature increases?
Shifts left (treat heat as a product).
If K = [products]/[reactants], how can you use this with RICE tables?
Plug E values into K expression to solve for x.
Given Kc and Δn = 2, convert to Kp. Use the formula.
Kp = Kc(RT)^Δn
Common ion effect: Add NaF to saturated CaF₂. What happens?
F⁻ increases → shifts left → less CaF₂ dissolves.
A reaction has K = 1.2 × 10⁵. What does this tell you about the equilibrium position?
Favors products; lies far to the right.
CO(g) + Cl₂(g) ⇌ COCl₂(g): What happens if volume decreases?
Shifts right — fewer gas moles (2 → 1).
If K is small, what assumption can simplify solving RICE problems?
Assume x is small → drop x in denominator if K < 10⁻³.
When is it appropriate to compare Kc and Kp values?
Only when all species are gases and Δn is known.
You mix two solutions and a precipitate forms. What inequality involving Q and Ksp explains this?
Q > Ksp → precipitation occurs.