Unit 10: Chemical Equilibrium Quiz

Which of the following cannot alter the position of a chemical equilibrium?

• Increasing the amount of catalyst

• Increasing the reactant concentration

• Increasing the temperature

• Increasing the total pressure

Answer explanation

Increasing the amount of catalyst does not change the position of a chemical equilibrium; it only speeds up the rate at which equilibrium is reached. The other options can shift the equilibrium position.

What are the units of the equilibrium constant (Kc) for the hypothetical reaction below? 2A(aq) + B(aq) ⇌ 4C(aq) + D(aq)

• mol² dm⁻⁹

• mol⁻² dm⁹

• mol² dm⁻⁶

• mol⁻² dm⁶

Answer explanation

To find the units of Kc, use the formula Kc = [C]^4[D] / [A]^2[B]. The units are (mol/dm³)⁴ / (mol/dm³)²(mol/dm³) = mol⁻² dm⁶, which is the correct choice.

Ammonium chloride decomposes on heating: NH₄Cl(s) ⇌ NH₃(g) + HCl(g) The equilibrium constant, Kp, for this reaction equals

• 0

• 1

• 2

• 3

Answer explanation

The equilibrium constant Kp for the decomposition of NH₄Cl is derived from the partial pressures of the products. At equilibrium, the ratio of the products' pressures to the reactants' pressure equals 1, hence Kp = 1.

This question is about equilibrium systems. The equilibrium for the reaction between hydrogen gas and an oxide of iron is:

The Kc expression for this equilibrium is:

• 
• 
• 
• 

What is the oxidation number of chlorine in Cl₂O₇?

• −1

• +1

• −7

• +7

Answer explanation

In Cl₂O₇, the total oxidation state of oxygen is -14 (7 O atoms at -2 each). To balance this, chlorine must have an oxidation number of +7 (2 Cl atoms at +7 each). Thus, the correct answer is +7.

A solution of iodine in aqueous potassium iodide is brown. The following equilibrium exists in this solution. What would be the effect, if any, on the colour of the solution if five drops of dilute sodium hydroxide solution were added to 5 cm³ of the iodine solution?

• No visible change.

• The colour gets lighter.

• The mixture turns colourless.

• The mixture goes a darker colour.

Answer explanation

Adding sodium hydroxide to the iodine solution reacts with iodine, forming iodide ions, which are colorless. This reaction removes the brown color, resulting in a colorless mixture.

This question is about the decomposition of dinitrogen tetroxide. The reaction eventually reaches equilibrium. What is the chemical formula for dinitrogen tetroxide?

• N2O4

• NO2

• N2O

• NO

Answer explanation

Dinitrogen tetroxide is a chemical compound composed of two nitrogen atoms and four oxygen atoms, represented by the formula N2O4. This distinguishes it from the other options, which represent different compounds.

What happens to the position of the equilibrium and the colour of the mixture when the pressure is increased? The volume of the system remains constant.

• moves to the right, mixture gets lighter

• moves to the right, mixture gets darker

• moves to the left, mixture gets lighter

• moves to the left, mixture gets darker

Answer explanation

Increasing pressure shifts the equilibrium to the side with fewer moles of gas. If the reaction produces lighter-colored products, the mixture will appear lighter. Thus, the correct answer is that it moves to the right, and the mixture gets lighter.

Which is the expression for the equilibrium constant, Kc, for the reaction NH₂COONH₄(s) ⇌ 2NH₃(g) + CO₂(g)? All concentration terms are at equilibrium.

• [NH₃][CO₂] / [NH₂COONH₄]

• [2NH₃][CO₂] / [NH₂COONH₄]

• [NH₃]²[CO₂]

Answer explanation

The equilibrium constant Kc is defined using the concentrations of products over reactants. For the reaction NH₂COONH₄(s) ⇌ 2NH₃(g) + CO₂(g), Kc = [NH₃]²[CO₂] since solids do not appear in the expression.