Honors Unit 8 - Equilibrium

Which statement best describes chemical equilibrium?

• All reactions stop
• Reactant concentrations equal product concentrations
• The forward and reverse reaction rates are equal
• Only products are formed
• The system is static

Answer explanation

At equilibrium, forward and reverse reaction rates are equal.

Which system is required for equilibrium to be established?

• Open system
• Closed system
• Isolated system
• Vacuum
• Diluted solution

Answer explanation

A closed system prevents loss of mass, allowing equilibrium.

Choose all true about dynamic equilibrium.

• Reactants are still converting to products
• Reaction rates are equal
• Reactants and products stop reacting
• It requires constant temperature
• Concentrations remain constant

Answer explanation

Equilibrium is dynamic with balanced rates and constant conditions.

Fill in the blank: A reaction is at equilibrium when the ______ of the forward and reverse reactions are equal.

Answer explanation

Equilibrium occurs when the reaction rates match.

In the system N₂O₄(g) ⇌ 2NO₂(g), what would you observe as the reaction proceeds toward equilibrium?

• Colorless gas becomes more intense brown and stays
• No color change
• Gas turns yellow
• Brown gas fades away completely
• Solution turns pink

Answer explanation

NO₂ is brown; as it forms, color intensifies until equilibrium.

Which species are included in an equilibrium expression?

• Solids and liquids
• Only gases
• Aqueous and gases
• All phases
• Only reactants

Answer explanation

Only (aq) and (g) species are included in equilibrium expressions.

Write the correct K expression for: 2NO(g) + O₂(g) ⇌ 2NO₂(g)

• K = [NO₂]^2 / ([NO]^2 * [O₂])
• K = [NO]^2 * [O₂] / [NO₂]^2
• K = [NO]^2 / [NO₂] * [O₂]
• K = [NO₂] / [NO] + [O₂]
• K = [O₂] / [NO]^2

Answer explanation

K uses products over reactants, each raised to stoichiometric coefficients.

Choose all true about equilibrium constants.

• K changes with temperature
• K is unitless
• K includes only (g) and (aq)
• Solids are excluded
• K determines rate

Answer explanation

K is temperature-dependent and excludes solids/liquids.

Fill in the blank: K = [products]^coeff / [reactants]^coeff is known as the ______.

Answer explanation

Equilibrium law is called the Law of Mass Action.

Which expression represents Kp?

• Uses molarities
• Includes solids
• Uses partial pressures
• Involves ΔG
• Excludes gases

Answer explanation

Kp uses partial pressures instead of molarities.