Unit 4.2 Review

Unit 4.2 Review
Reaction Rates and Equilibrium

Unit 4.2 - Rates of Reaction and Equilibrium

Reaction Rates
Reversible Reactions
Equilibrium Expressions
Le Chatelier's Principle

Rates of Reaction

Dependant on frequency and energy of collisions
Rate slows as reaction progresses
Affected by
Temperature (frequency and energy)
Concentration (frequency)
Pressure (frequency)
Surface area (frequency)
Catalyst (energy)

Multiple Choice

Why does a higher temperature increase the rate of a reaction?

• it increases both the frequency and energy of particle collisions
• it only increases the frequency of particle collisions
• it only increases the energy of particle collisions
• it reduces the activation energy of the reaction

Multiple Choice

Why does a higher concentration increase the rate of reaction?

• it increases the amount of reactants
• it lowers the activation energy
• it increases the energy of particle collisions
• it increases the frequency of particle collisions

Multiple Choice

How does a catalyst work in speeding up a reaction?

• by lowering the activation energy

• by giving them more energy

• by making them more available

Multiple Choice

Grinding a seltzer tablet into powder increases the rate of reaction due to increased

• concentration
• surface area
• temperature
• reactants

Reversible Reactions

Most reactions proceed both forward and backward
In a system at equilibrium, the rate of reaction is equal in both directions

Multiple Choice

Which of the following reactions is reversible?

• H_{2 +} I₂ ⇌ 2HI

• C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O

• NaOH + HCl → NaCl + H₂O

• CuSO₄ + Zn → ZnSO₄ + Cu

Multiple Choice

What are the two factors to look for when determining if the reaction is at equilibrium?

• Forward reaction rate is faster than the reverse and concentrations are equal
• Forward and reverse reaction rates are equal and concentration is constant

• Forward and reverse reaction rates are equal and concentration is equal

• Forward reaction rate is faster than the reverse and concentration is equal

Equilibrium Expressions

Multiple Choice

What is the equilibrium constant expression for the reaction:

2 BrF_5(g) —> Br_2(g) + 5 F_2(g)

• Kc = [Br₂] [F₂] / [BrF_5]

• Kc = [BrF₅]² / [Br₂][F₂]⁵

• Kc = [Br₂] [F₂]⁵ / [BrF₅]²

• Kc = 2[BrF₅]² / ([Br₂] × 5[F₂]⁵)

• Kc = [Br₂] [F₂]² / [BrF₅]⁵

Multiple Choice

Calculate the equilibrium constant for the following reaction:
SO₂ (g) + NO₂ (g) <=> SO₃ (g) + NO (g)
[SO₃] = 0.40 M, [NO] = 0.30 M, [NO₂] = 0.15 M, and [SO₂] = 0.20 M.

• 4
• .42
• .25
• 1

Multiple Choice

Which is the correct equilibrium constant expression for the following reaction?

Fe₂O_3(s) + 3 H_2(g) —> 2 Fe_(s) + 3 H₂O_(g)

• K = [H₂O]³ / [H₂]³

• K = [Fe₂O₃] [H₂]³ / [Fe]²[H₂O]³

• K = [Fe]²[H₂O]³ / [Fe_2O₃] [H₂]³

• K= [Fe] [H₂O] / [Fe₂O₃] [H₂]

• K = [H₂] / [H₂O]

Multiple Choice

An equilibrium constant with a large magnitude indicates…

• A very fast reaction
• More products at equilibrium
• More reactants at equilibrium
• nothing, without considering the stoichiometry of the reaction

Le Chatelier's Principle

A system disturbed from equilibrium will react to restore equilibrium
Allows us to predict how reaction will shift from changes in
Concentration (or moles)
Pressure
Temperature

Multiple Choice

If the concentration of SO_{2 (g)}  is increased, the equilibrium of the reaction will _____.
SO_{2 (g)} + O_{2 (g)} <−>  SO_{3 (g)}

• shift to the left
• shift to the right
• not shift

Multiple Choice

If the heat is removed from the chemical system, the equilibrium will _______.
heat  +  N_2(g)  +  O_2(g)  <−>  2NO_(g)

• shift to the left
• shift to the right
• not shift

Multiple Choice

If the pressure in the following system is increased, the reaction will ____________.
N_{2 (g)} +  3 H_2 (g) <−> 2 NH_{3 (g)}

•  shift to the left
• shift to the right
• not shift