# Quiz | Chemical Equilibrium

1

Which of the following statements about the equilibrium constant is correct?

It changes with changes in the temperature

It changes by the addition of a catalyst

It always remains the same at different reaction conditions

It increases if the concentration of one of the reactants or products is increased

According to Le Châtelier's principle, if a dynamic equilibrium is disturbed by changing the conditions, the equilibrium position moves to counteract the change. The quantities whose change may affect an equilibrium are the concentration of a reactant or product, the volume, the pressure and the temperature

2

Which of the following statements is correct?

At the equilibrium, sum of [reactant] = sum of [product]

At the equilibrium the forward and reverse reactions still occur

A chemical equilibrium can be attained only starting from a mixture

Chemical equilibrium is a static equilibrium, [reactant] = constant and [product] = constant

Chemical equilibrium is a dynamic equilibrium: the forward and reverse reactions still occur but reactants and products are formed at such rate that their concentration does not change

3

What is the equilibrium constant expression KC of the reaction: N(g) + 3 H(g) $⇄$ 2 NH(g)?

$\frac{\left[{\mathrm{N}}_{2}\right]\left[{\mathrm{H}}_{2}\right]}{\left[{\mathrm{NH}}_{3}\right]}$

$\frac{\left[{\mathrm{NH}}_{3}\right]}{\left[{\mathrm{N}}_{2}\right]\left[{\mathrm{H}}_{2}\right]}$

$\frac{\left[{\mathrm{N}}_{2}\right]{\left[{\mathrm{H}}_{2}\right]}^{3}}{{\left[{\mathrm{NH}}_{3}\right]}^{2}}$

$\frac{{\left[{\mathrm{NH}}_{3}\right]}^{2}}{\left[{\mathrm{N}}_{2}\right]{\left[{\mathrm{H}}_{2}\right]}^{3}}$

Equilibrium constant KC: ratio of product concentrations to reactant concentrations at the equilibrium
The concentrations are raised to a power equal to the stoichiometric coefficient

4

What is the equilibrium constant expression KC of the reaction: 2 ICl (s) $⇄$ I(s) + Cl(g)?

[Cl2]

$\frac{\left[{\mathrm{I}}_{2}\right]}{{\left[\mathrm{ICl}\right]}^{2}}$

$\frac{\left[{\mathrm{Cl}}_{2}\right]\left[{\mathrm{I}}_{2}\right]}{{\left[\mathrm{ICl}\right]}^{2}}$

Equilibrium constant KC: ratio of product concentrations to reactant concentrations at the equilibrium
Pure solids reactants and products do not appear in the equilibrium-constant expression (= 1 by convention)

5

How can we increase the total amount of produced Cl2 during the reaction: 2 ICl (s) $⇄$ I(s) + Cl(g)?

By increasing the pressure

By removing the Cl2 as it is formed

By decreasing the volume of the container

According to Le Chatelier’ principle, the position of equilibrium will move in such a way as to counteract the change: by removing the Cl2 as it is formed, the equilibrium will move to the right to produce more Cl2

Additionally, the right is the side with most moles of gas. The equilibrium will move to the right if the concentration of a reactant decreases OR the volume increases OR the pressure decreases

6

What happens when the reaction quotient QC is less than the equilibrium constant K?

The reaction will move to the left

The reaction will move to the right

It depends on whether the reaction is endothermic or exothermic

It depends on the reaction conditions

Reaction quotient QC: ratio of product concentrations to reactant concentrations at a given time
If QC < K, the reaction will move to the right ⇒ net formation of product