Leaving Cert Chemistry (Ordinary) - Chemical Equilibrium

Multiple Choice Quiz

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A chemical reaction that does not go to completion is said to be in a state of
1. dynamic equilibrium
2. static equilibrium
3. neither of the other options
Which one of the following reactions is most unlikely. to reach completion?
1. The reaction between nitrogen gas and hydrogen gas.
2. The burning of magnesium in oxygen gas.
3. A neutralisation reaction between hydrochloric acid and sodium hydroxide.
4. Sodium metal reacting with water.
Ammonia is important in the manufacture of fertilizers. It is made by reacting nitrogen and hydrogen. The process for this reaction was developed by
1. Fritz Haber
2. Justus Von Liebig
3. Wilhelm Bunsen
4. Erwin Schrodinger
A chemical reaction has reached dynamic equilibrium at a certain temperature. Which one of the following statements is incorrect?
1. The reaction has stopped completely.
2. The rate of the forward reaction is equal to the rate of the reverse reaction.
3. Products are continuously being formed.
4. The concentrations of the reactants remains constant.
The diagram shows the concentrations of hydrogen, iodine and hydrogen iodide for the reaction between hydrogen and iodine.
Which one of the following statements is INCORRECT?
1. At point A on the time axis, the concentration of all three gases is zero.
2. The reaction between the gases reaches equilibrium at point B.
3. At point C, the system is in a state of dynamic equilibrium.
4. Adding more hydrogen at point D will alter the shape of the graph.
Le Chatelier's Principle states that if a _____________ is applied to at system at ____________, the system readjusts to minimise the stress causing it.
From the list below, select the respective words that are missing.
1. stress, equilibrium
2. stress, rest
3. pressure, equilibrium
4. pressure, rest
The reaction of nitrogen dioxide (NO₂) forming dinitrogen tetroxide (N₂O₄) is exothermic in the forward direction.

What two conditions will cause the equilibrium mixture to go dark brown?
1. Increase in temperature
2. Decrease in pressure
3. Increase in pressure
4. Adding more catalyst
When heat is applied to a system at equilibrium
1. the system absorbs the heat
2. the system releases the heat
3. more product(s) is/are formed
4. the temperature of the system increases
In the reaction

Select three ways of increasing the yield of ammonia (NH₃)
1. Add more hydrogen (H₂)
2. Lower the temperature
3. Remove the ammonia (NH₃) as it forms
4. Remove the nitrogen (N₂) as it forms.
5. Increase the temperature.
6. Add a catalyst
7. Lower the pressure
The reaction between hydrogen (H₂) and nitrogen (N₂) is described by the equation

What will be the effect of increasing the concentration of ammonia (NH₃)?
1. More hydrogen (H₂) is formed
2. More ammonia (NH₃) is formed
3. Less nitrogen (N₂) is formed
4. The temperature increases
Which one of the following equilibrium reactions is not affected by a change in pressure?
The reaction

is not affected by a change in pressure. Why is this?
1. There are equal numbers of molecules on both sides of the equation.
2. They are all in the gaseous state.
3. Because it is an endothermic reaction.
4. It is a catalysed reaction.
Consider the equilibrium reaction

What effect will adding a catalyst have on this reaction?
1. The system reaches equilibrium faster.
2. More CH₃COOC₂H₅ is formed.
3. More C₂H₅OH is formed.
4. Less H₂O is formed.
The following equilibrium mixture is a purple colour.

According to Le Chatelier's Principle, what will happen when water is added to the mixture?
1. It will go red as more Co(H₂O)₆²⁺ is formed.
2. It stays a violet colour as the water is neutral.
3. It will turn blue as CoCl₄^{2-^{is being formed.}}
4. The water causes more Cl^- ions to form and these ions cause a change in the colour to red.
Consider the following equilibrium reaction

Which one of the following will cause a yellow colour to predominate?
1. Addition of sodium hydroxide (NaOH)
2. Addition of hydrochloric acid (HCl)
3. Removal of water
4. Addition of sodium chromate (Na₂CrO₄)
Solutions of iron (III) chloride and potassium thiocyanate are mixed together and the following equilibrium mixture is set up:

The resulting mixture is red.
Which one of the following reagents must be added to change the colour of the mixture to yellow?
1. Dilute hydrochloric acid
2. Water
3. Iron (III) chloride solution (FeCl₃)
4. Potassium cyanide (KCNS)
What colour change will occur if concentrated sulfuric acid (H₂SO₄) is added to the following equilibrium mixture?
1. Yellow to orange
2. Orange to yellow
3. Orange to green
4. Green to orange
The forward reaction of the equilibrium system below is endothermic. Dilute HCl is added and the colour changes to blue.

What colour change occurs when the mixture is cooled?
1. Blue to pink
2. Pink to blue
3. No colour change
The equation

describes the Haber Process. According to Le Chatelier's Principle, a high yield of ammonia is favoured at a high pressure and low temperature.
However this is not practical.
Select two reasons from the list below why this is so.
1. The materials required to build a high pressure plant would be expensive.
2. At low temperatures, reactions are slower because less energy is available.
3. At low temperatures, other products besides ammonia are formed.
4. At high pressures, the particles of the two reacting gases are too far apart to react.
The Contact Process for making sulfuric acid involves two steps.

In the first stage, Le Chatelier's Principle suggests that high pressure and low temperature would produce more SO₃.
But this is not the case. Select two reasons why this is so.
1. Building high pressure plants is uneconomical.
2. Low temperatures would lower the rate of production.
3. High pressure would liquefy the oxygen.
4. It is more costly at low temperaturtes.
The reaction between SO₂ and O₂ may be described as

Select the two conditions that will favour a high yield of SO₃
1. Addition of more O₂
2. Lower the temperature
3. Lower the pressure
4. Removal of SO₂
5. Using a catalyst
For the reaction

what is its correct equilibrium constant?
Consider the general equilibrium reaction

Which one of the following represents the correct equilibrium constant for this reaction?
The equilibrium constant for the reaction

is:
The Haber Process may be described by the equation

The equilibrium constant for this process is
Which one of the following statements is correct?
1. When K_c is very large, there are more products formed.
2. K_c does not depend on temperature
3. K_c never has units.
4. The value of K_c gives us the rate of reaction.