Equilibrium

At equilibrium

• All chemical processes have stopped.

• The [Reactants] = [Products]

• The concentration of the reactants and products are constant and no longer change.

• The energy levels of the reactants and products are the same.

Which of these will change the value of the equilibrium constant?

• Increasing the initial concentration of a reactant.

• Increasing the temperature of the system.

• Increasing the pressure for a gas phase reaction.

• All of these will change the equilibrium constant.

Tags

NGSS.HS-PS1-6

Which of the following is NOT true at equilibrium?

• The forward and reverse reactions proceed at the same rate.
• The concentrations of reactants and products remain constant.

• The concentration of the reactants is equal to the concentration of the products.
• Interconversions between reactants and products still proceed.

Select the equilibrium constant for the most reactant favored system.

Answer explanation

Reactant favored means more reactants so it is the smallest K value.

When Q is greater than K_c what will happen?

• The [Reactants] will increase and [Products] will decrease.

• The [Reactants] will decrease and [Products] will increase.

• The [Reactants] and [Products] will both increase.

• The [Reactants] and [Products] will both decrease.

Answer explanation

If Q is greater than K, the concentration of products is too high so which way would the reaction shift to attain equilibrium?

What is the equilibrium expression for:

Fe₃O₄(s) + 4H₂(g) ⇄ 3Fe(s) + 4H₂O(g)

K_c =

Answer explanation

Omit pure solids and liquids from K!

For the reaction

N_{2 (g)} + 3 H_2(g) ⇄ 2 NH_{3 (g)}

If the pressure in the system is increased, which substance(s) will have a higher conentration after equilibrum is reattained?

• all 3 gases

• N₂ and H₂

• NH₃

• The concentrations wouldn't change.

Answer explanation

Increasing the pressure causes the volume to decrease, so which way would the reaction shift?

Compare the number ot reactant and product gas molecules to predict the direction.

Tags

NGSS.HS-PS1-6

2 SO₂(g) + O₂(g) ⇄ 2 SO₃(g)

Adding SO₂(g) will

• shift equilibrium right

• shift equilibrium left

• increase K_c

• not cause a shift

Answer explanation

An equilibrium reaction shifts away (to the opposite side) when a reactant or product concentration is increased.

Tags

NGSS.HS-PS1-5

2 SO₂(g) + O₂(g) ⇄ 2 SO₃(g)

Removing O₂(g) will

• shift equilibrium right

• shift equilibrium left

• increase pressure

• have no change

Answer explanation

An equilibrium reaction shifts towards the side that has a decreased reactant or product concentration to form more of the chemical that was removed.

Decreasing the temperature of an endothermic reaction will cause

• equilibria to shift left and K increases

• equilibria to shift left and K decreases

• equilibria to shift right and K increases

• equilibria to shift right and K decreases

Answer explanation

For endothermic reactions, heat is absorbed so it acts like a reactant.

Tags

NGSS.HS-PS1-5