Try this as often as you like. You will get a different set of questions each time you attempt this quiz.
A chemical reaction that does not go to completion is said to be in a state of
dynamic equilibrium
static equilibrium
neither of the other options
Which one of the following reactions is most unlikely to reach completion?
The reaction between nitrogen gas and hydrogen gas.
The burning of magnesium in oxygen gas.
A neutralisation reaction between hydrochloric acid and sodium hydroxide.
Sodium metal reacting with water.
When a chemical reaction has reached a dynamic state
the reactants are forming products while the products are forming reactants.
the reactants are no longer reacting.
the products are forming faster than they are being converted back into reactants.
there are no longer any reactants left.
Ammonia is important in the manufacture of fertilizers. It is made by reacting nitrogen and hydrogen. The process for this reaction was developed by
Fritz Haber
Justus Von Liebig
Wilhelm Bunsen
Erwin Schrödinger
A chemical reaction has reached dynamic equilibrium at a certain temperature. Which one of the following statements is incorrect?
The reaction has stopped completely.
The rate of the forward reaction is equal to the rate of the reverse reaction.
Products are continuously being formed.
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?
At point A on the time axis, the concentration of all three gases is zero.
The reaction between the gases reaches equilibrium at point B.
At point C, the system is in a state of dynamic equilibrium.
Adding more hydrogen at point D will alter the shape of the graph.
Le Châtelier'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.
stress, equilibrium
stress, rest
pressure, equilibrium
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?
When heat is applied to a system at equilibrium
the system absorbs the heat.
the system releases the heat.
more product(s) is/are formed.
the temperature of the system increases.
In the reaction N2 + 3H2 ⇋ 2NH3 ΔH = -92.4 kJ/mol Select three ways of increasing the yield of ammonia (NH3)
The reaction between hydrogen (H2) and nitrogen (N2) is described by the equation N2 + 3H2 ⇋ 2NH3 ΔH = -92.4 kJ/mol What will be the effect of increasing the concentration of ammonia (NH3)?
More hydrogen (H2) is formed
More ammonia (NH3) is formed
Less nitrogen (N2) is formed
The temperature increases
Which one of the following equilibrium reactions is not affected by a change in pressure?
H2(g) + I2(g) ⇋ 2HI(g)
PCl3(g) + Cl2(g) ⇋ PCI5(g)
2NO2(g) ⇋ N2O4(g)
N2(g) + 3H2(g) ⇋ 2NH3(g)
The reaction H2(g) + I2(g) ⇋ 2HI(g) ΔH = +53 kJ/mol . is not affected by a change in pressure. Why is this?
There are equal numbers of molecules on both sides of the equation.
They are all in the gaseous state.
Because it is an endothermic reaction.
It is a catalysed reaction.
Consider the equilibrium reaction C2H5OH + CH3COOH ⇋ CH3COOC2H5 + H2O What effect will adding a catalyst have on this reaction?
The system reaches equilibrium faster.
More CH3COOC2H5 is formed.
More C2H5OH is formed.
Less H2O is formed.
When cobolt (II) chloride is added to water, the following equilibrium is set up with the red colour predominant. On adding dilute HCl, the colour changes to blue. Why does this happen?
Addition of chloride ions shifts the equilibrium to the left.
The equilibrium shifted to the right.
Because water changes the colour of the system to blue.
More Cl- ions were formed.
The following equilibrium mixture is a purple colour According to Le Châtelier's Principle, what will happen when water is added to the mixture?
It will go red as more Co(H2O)62+ is formed.
It stays a violet colour as the water is neutral.
It will turn blue as CoCl42- is being formed.
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?
Addition of sodium hydroxide (NaOH)
Addition of hydrochloric acid (HCl)
Removal of water
Addition of sodium chromate (Na2CrO4)
For the equilibrium reaction dilute HCl is added to the mixture. Select two statements to describe what is happening.
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?
Dilute hydrochloric acid
Water
Iron (III) chloride solution (FeCl3)
Potassium cyanide (KCNS)
What colour change will occur if concentrated sulfuric acid (H2SO4) is added to the following equilibrium mixture?
Yellow to orange
Orange to yellow
Orange to green
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?
Blue to pink
Pink to blue
No colour change
Henri Le Châtelier studied equilibrium reactions in industry in the late 19th century. According to Le Châtelier’s principle, what effect would an increase in pressure have on the yield of ammonia at equilibrium?
There would be a greater yield of ammonia.
The yield of ammonia would be less.
It would have no effect on the yield of ammonia.
More hydrogen and nitrogen are formed.
Ammonia is formed in the Haber process according to the following balanced equation N2 + 3H2 ⇋ 2NH3 ΔH = -92.4 kJ/mol The table shows the percentages of ammonia present at equilibrium under different conditions of temperature T and pressure P when hydrogen and nitrogen gases were mixed in a 3:1 molar ratio. From the table, what conditions of temperature and pressure will give the highest yield of ammonia.
1000 atm and 573 K
1000 atm and 773 K
10 atm and 573 K
100 atm and 573 K
Ammonia is formed in the Haber process according to the following balanced equation: N2(g) + 3H2(g) ⇋ 2NH3(g) ΔH = -92.4 kJ/mol The table shows the percentages of ammonia present at equilibrium under different conditions of temperature T and pressure P when hydrogen and nitrogen gases were mixed in a 3:1 molar ratio. Is this an endothermic or exothermic reaction? Select the correct reason for your answer.
It is exothermic because as the temperature decreases, the yield increases. Lowering the temperature favours an exothermic reaction.
It is exothermic because as the pressure increases, the yield increases. Increasing the pressure favours an exothermic reaction.
It is endothermic because as the temperature decreases, the yield increases. Lowering the temperature favours an endothermic reaction.
It is exothermic because as the pressure increases, the yield increases. Increasing the pressure favours an exothermic reaction.
The equilibrium constant for the Haber Process is If a catalyst is used in this process, what effect will it have on the value of Kc?
A catalyst will have no effect.
A catalyst will change equilibrium to the left.
A catalyst will change equilibrium to the right.
The equation N2(g) + 3H2(g) ⇋ 2NH3(g) ΔH = -92.4 kJ/mol describes the Haber Process. According to Le Châtelier'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.
The Contact Process for making sulfuric acid involves two steps: 2SO2(g) + O2(g) ⇋ 2SO3(g) ΔH = -196 kJ/mol SO3(g) + H2O ⇋ H2SO4(l) In the first stage, Le Châtelier'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.
The reaction between SO2 and O2 may be described as 2SO2(g) + O2(g) ⇋ 2SO3(g) ΔH = -196 kJ/mol Select the two conditions that will favour a high yield of SO3
For the reaction H2(g) + I2(g) ⇋ 2HI(g) what is its correct equilibrium constant?
Consider the general equilibrium reaction pA + qB ⇋ rC + sD Which one of the following represents the correct equilibrium constant for this reaction?
The equilibrium constant for the reaction 2HI(g) ⇋ H2(g) + I2(g) is:
The Haber Process may be described by the equation N2(g) + 3H2(g) ⇋ 2NH3(g) The equilibrium constant for this process is
If Kc = 2.5 for the reaction N2(g) + 3H2(g) ⇋ 2NH3(g) then
the equilibrium lies predominantly to the right.
the equilibrium lies predominantly to the left.
there is 2.5 times as much ammonia as nitrogen.
the reaction has gone to completion.
Which one of the following statements is correct?
When Kc is very large, there are more products formed.
Kc does not depend on temperature.
Kc never has units.
The value of Kc gives us the rate of reaction.
For the reaction H2(g) + I2(g) ⇋ 2HI(g) at equilibrium, in a 1 litre container, the amount of H2 is 1 mole, the amount of I2 is 2 moles & the amount of HI is 2 moles. What is Kc for this reaction?
2
1
1.33
0.5
Three moles of ethanol and three moles of ethanoic acid were reacted together according to the equation C2H5OH + CH3COOH ⇋ CH3COOC2H5 + H2O At equilibrium, there were 2 moles each of ethyl ethanoate (CH3COOC2H5) and water formed. What is the equilibrium constant for this reaction?
4
2
0.25
0.44
0.5 mole of PCl5 was placed in a 4 litre sealed container. The PCl5 decomposed according to the equation PCl3(g) + Cl2(g) ⇋ PCI5(g) When the reaction had reached equilibrium, there were 0.2 mole of PCl3 and Cl2 present in the container. Which one of the following is the correct dissociation constant for this reaction?
0.033
7.5
0.133
33
For the reaction H2(g) + I2(g) ⇋ 2HI(g) the equilibrium constant, Kc is 49 at a fixed temperature. Two moles of hydrogen and two moles of iodine are allowed to reach equilibrium at this temperature. What is the concentration of hydrogen iodide at equilibrium?
1.55
9.2
0.77
1.75
Which change will increase the equilibrium concentration of sulfur trioxide in this reaction? 2SO2(g) + O2(g) ⇌ 2SO3(g) 2SO2(g)H = negative
Increasing the pressure
Decreasing the concentration of oxygen
Using a catalyst
Increasing the temperature
The equation below describes an equilibrium reaction occurring in a closed system. A(g) + B(g) ⇌ 4C(g) ΔH = +58 kJ Under which set of the following conditions would the highest yield of C(g) be obtained?
Temperature = 300oC, Pressure = 100 kPa
Temperature = 50oC, Pressure = 100 kPa
Temperature = 50oC, Pressure = 200 kPa
Temperature = 300oC, Pressure = 200 kPa
Consider the following equilibrium reaction in a closed container at 50 °C. SO2(g) + Cl2(g) ⇌ SO2Cl2(g), ΔH = -85 kJ Which of the following statements is correct?
Decreasing the temperature will increase the amount of SO2Cl2(g)
Increasing the volume of the container will increase the amount of SO2Cl2(g)
Increasing the temperature will increase the amount of SO2Cl2(g)
Adding a catalyst will increase the amount of SO2Cl2(g)
A 1.0 litre reaction vessel initially contains 6.0 mol of P and 6.0 mol of Q. At equilibrium 4.0 mol of R is present. What is the value of Kc for the following reaction? P(g)+ Q(g) ⇌ R(g)+ S(g)
4.00
0.44
0.11
0.25
The equation for the Haber process is: N2(g) + H2 → 2NH3(g) ΔH = − 92.2kJ Which conditions will favour the production of the greatest amount of ammonia at equilibrium?
Low temperature and high pressure
High temperature and high pressure
High temperature and low pressure
Low temperature and low pressure
Which changes cause an increase in the equilibrium yield of SO (g) in this reaction? 2SO2(g) + O2(g) ⇌ 2SO3(g), ΔH = −196 kJ 1. Increasing the pressure 2. Decreasing the temperature 3. Adding oxygen
1, 2 and 3
1 and 2 only
2 and 3 only
1 and 3 only
The equation for a reversible reaction used in industry to convert methane to hydrogen is shown below. CH4(g) + H2O(g) → CO(g) + 3H2(g), ΔH = +210 kJ Which statement is always correct about this reaction when equilibrium has been reached?
The value of ΔH for the reverse reaction is −210 kJ .
The concentrations of methane and carbon monoxide are equal.
The rate of the forward reaction is greater than the rate of the reverse reaction.
The amount of hydrogen is three times the amount of methane.
The expression for the equilibrium constant for a reaction is At a certain temperature the values of [A], [B] and [C] are all 0.2 mol dm−1. What happens to the value of Kc when all three values are doubled to 0.4 mol dm−1?
There is no change
It is halved.
It doubles.
It increases by a factor of four.
For the reaction below H2(g) + I2(g) ⇌ 2HI(g) at a certain temperature, the equilibrium concentrations are (in mol dm−3) [H2] = 0.30, [I2] = 0.30, [HI] = 3.0 What is the value of K?
100
5.0
15
10
The value of the equilibrium constant for the reaction2HI(g) ⇌ H2(g) + I2(g) is 0.25 at 440 °C . What would the value of the equilibrium constant be for the following reaction at the same temperature?H2(g) + I2(g) ⇌ 2HI(g)
4.0
0.5
0.25
2.0
A few drops of concentrated sulphuric acid were added to a mixture of 0·1 mol of methanol and 0·2 mol of ethanoic acid. Even after a considerable time, the reaction mixture was found to contain some of each reactant. Which one of the following is the best explanation for the incomplete reaction?
An equilibrium mixture was formed.
The temperature was too low.
Insufficient methanol was used.
Insufficient ethanoic acid was used.
Which of the following applies correctly to the use of a catalyst in a chemical reaction?
No change in equilibrium, no change in ΔH
No change in equilibrium, increase in ΔH value
Equilibrium shifts to right, decrease in ΔH value
Equilibrium shifts to left, no change in ΔH
What will happen to the position of equilibrium and the value of the equilibrium constant when the temperature is increased in the following reaction: Br2(g) + Cl2(g) ⇌ 2BrCl(g), ΔH = +14 kJ
Equilibrium shifts towards the products and the equilibrium constant increases
Equilibrium shifts towards the reactants and the equilibrium constant decreases
Equilibrium shifts towards the reactants and the equilibrium constant increases
Equilibrium shifts towards the products and the equilibrium constant decreases
Carbonic acid is formed by dissolving carbon dioxide in water. This equilibrium is represented by the following equation. CO2 + H2O ⇌ H2CO3 If carbon dioxide is removed from this equilibrium mixture, the pH will
increase
decrease
remain approximately constant because the concentration of the hydrogencarbonate changes to compensate.
remain approximately constant because the concentration of the carbonic acid changes to compensate.