Chemical Equilibrium Lecture Notes

Flashcards covering the fundamentals of chemical equilibrium, including static vs. dynamic states, equilibrium constants (Kc, Kp), the reaction quotient (Q), and ICE table calculations based on the lecture notes.

When does static equilibrium occur?

Static equilibrium occurs when an object or system is at rest and there is no visible motion or change.

What is the definition of dynamic equilibrium?

Dynamic equilibrium occurs when two opposite processes continue at equal rates, so no overall change is observed.

According to the Main Idea, what happens to the concentrations of reactants and products at equilibrium?

At equilibrium, the concentrations of reactant and products remain constant.

What is the chemical equation for the decomposition of heated mercury(II) oxide?

$$2HgO(s) \rightarrow 2Hg(l) + O_2(g)$$

What characterizes chemical equilibrium in terms of reaction rates?

The rate of the forward reaction equals the rate of the reverse reaction.

How is a closed system defined in the context of equilibrium?

A closed system allows energy transfer but does not allow matter to enter or leave, making equilibrium possible.

What does it mean if a chemical equilibrium "lies to the right"?

It means the forward reaction is predominant and at equilibrium there is a much higher concentration of products than of reactants.

What does it mean if a chemical equilibrium "lies to the left"?

It means the amounts of reactants remain high, the amounts of products are low, and the reactants are the predominant species.

For a general reaction $aA + bB \rightleftharpoons pP + qQ$, what is the equilibrium constant expression ($K_{c}$)?

$$K_{c} = \frac{[P]^{p}[Q]^{q}}{[A]^{a}[B]^{b}}$$

What units are used for the equilibrium constant $K_{c}$?

It is unitless.

What is the basis for the equilibrium constant $K_{p}$?

$K_{p}$ is based on partial pressures measured in atmospheres.

How does the magnitude of $K$ indicate the dominance of species at equilibrium?

If $K \text{ >> } 1$, products dominate and equilibrium lies to the right; if $K \text{ << } 1$, reactants dominate and equilibrium lies to the left.

What is the relationship between the equilibrium constant of a forward reaction and its reverse reaction?

The equilibrium constant for a reaction in one direction is the reciprocal of the equilibrium constant of the reaction in the opposite direction.

Why are pure solids and pure liquids ignored in equilibrium constant expressions?

Neither density nor molar mass is a variable, so the concentrations of solids and pure liquids are constant.

What are the four steps for solving equilibrium problems using an ICE table?

1. Write an equilibrium expression for the balanced reaction. 2. Write an ICE table and fill in given amounts. 3. Use stoichiometry on the change in concentration line. 4. Deduce equilibrium concentrations of all species.

What is the reaction quotient ($Q$)?

The reaction quotient ($Q$) is defined for a reaction at conditions not at equilibrium, using molarities at any time.

How can $Q$ and $K$ be used to predict the direction of a reaction?

If $Q > K$, the reverse reaction occurs (goes left); if $Q < K$, the forward reaction occurs (goes right).

Under what condition can the change in concentration ($x$) be approximated as insignificant in equilibrium calculations?

If the difference between $K_{eq}$ and initial concentrations is around 3 orders of magnitude or more.

What is the equilibrium constant expression for the reaction $2PbS(s) + 3O_{2}(g) \rightleftharpoons 2PbO(s) + 2SO_{2}(g)$?

$$K_{c} = \frac{[SO_{2}]^{2}}{[O_{2}]^{3}}$$