HHHS Mod 5 T1W8 Quiz

What mass of lead (II) iodide (MM = 461 g/mol) will dissolve in 375 mL of water?

• 1. 0.233 g

• 1. 0.293 g

• 1. 0.369 g

• 1. 0.621 g

Answer explanation

Which is the correct expression for calculating the solubility (in mol/L) of lead(II) iodide in a 0.1 mol/L solution of NaI at 25°C?

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Answer explanation

Silver iodide (AgI) is a sparingly soluble salt.
The Ksp of AgI at 25°C is 8.52 × 10⁻¹⁷.

How many times less soluble is silver iodide in 0.250 mol L⁻¹ KI than in pure water?

• 2.71 × 10⁷

• 7.38 × 10⁻⁸

• 1.08 × 10⁸

• 2.71 × 10⁸

Answer explanation

Lead(II) chloride (PbCl₂) is a sparingly soluble salt.
The Ksp of PbCl₂ at 25°C is 1.70 x 10^-5.

How many times less soluble is lead(II) chloride in 0.100 mol/L NaCl than in pure water?

• 9.53 x 10¹

• 1.62 x 10^-2

• 9.53

• 5.24

Answer explanation

The graph provided shows the number of moles of gasses A₂ (g), B₂​ and AB₂ in a 2L vessel. The reaction equation is:

A₂ (g) ​+2B₂​ (g) ⇌ 2AB₂ (g) ∆H = - 108 kJ/mol

What happened to the system at 10 minutes in?

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• The volume of the vessel was decreased.

• The temperature was decreased

• The volume of the vessel was increased

• The temperature was increased

Answer explanation

There is no sudden vertical jump at 10 minutes, so it is not a change in volume or concentration. The concentrations change gradually, which indicates a temperature change. After 10 minutes, AB₂ increases while A₂ and B₂ decrease, so the equilibrium shifts to the right. The forward reaction is exothermic (ΔH is negative), so heat is a product. Decreasing the temperature removes heat, so the system shifts right to produce more heat. Therefore, the temperature was decreased.

The graph provided shows the number of moles of gases A₂, B₂ and AB₂ in a 2 L vessel. The reaction is:

A₂(g) + 2B₂(g) ⇌ 2AB₂(g)  ΔH = −108 kJ mol⁻¹

What is the value of the equilibrium constant, K, for this system at equilibrium between t=5 and t=10 minutes?

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• 0.22

• 1.11

• 2.25

• 0.44

Answer explanation

Which of the following is the best explanation of collision theory?

• Chemical reactions occur when particles collide, regardless of their energy or orientation.

• Chemical reactions occur when particles collide with sufficient energy and correct orientation to form products.

• Chemical reactions occur when particles collide frequently, so that equilibrium is reached faster.

• Chemical reactions occur when particles collide and transfer energy to increase the equilibrium constant.

The energy profile diagram above shows the forward reaction for a reversible reaction.

What is the most likely effect of decreasing temperature on the forward and reverse reaction rates?

• The forward reaction rate decreases more because it has a lower activation energy to overcome.

• The reverse reaction rate decreases more because it has a higher activation energy to overcome.

• The reverse reaction rate increases because particles lose energy and favour the forward reaction.

• Both reaction rates decrease by the same amount because particles have less energy to collide.

Answer explanation

When temperature decreases, particles have less kinetic energy, so fewer particles have enough energy to react.

Both forward and reverse reaction rates decrease, but they do not decrease equally. The reverse reaction has a higher activation energy, so it needs more energy for particles to react. When temperature drops, a much smaller proportion of particles have enough energy to overcome this higher activation energy.

This means the reverse reaction rate decreases more than the forward reaction rate.

The energy profile diagram above shows the forward reaction for a reversible reaction.

Select ALL correct statements about this equilibrium system.

• The forward reaction is endothermic.

• The activation energy of the reverse reaction is less than that of the forward reaction.

• Increasing temperature increases the rate of both forward and reverse reactions.

• Increasing temperature increases the value of the equilibrium constant.

• Decreasing temperature increases the value of the equilibrium constant.

A blood-red solution contains an equilibrium mixture of iron(III) ions and thiocyanate ions:

Fe³⁺(aq) + SCN⁻(aq) ⇌ FeSCN²⁺(aq)

(colourless)(colourless)   (red)

The forward reaction is exothermic. What is the most likely effect of decreasing temperature on this system?

• The equilibrium shifts to the left and the solution becomes less red.

• The equilibrium shifts to the right and the solution becomes more red.

• The equilibrium constant decreases and the solution becomes less red.

• The equilibrium constant remains constant and the solution becomes more red.

Answer explanation

The forward reaction is exothermic, so heat is a product.

When temperature decreases, heat is effectively removed from the system. According to Le Chatelier’s principle, the equilibrium shifts to the right to produce more heat.

This forms more FeSCN²⁺, which is red, so the solution becomes more intensely red.