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Worksheets3.1.6 Chemical equilibria + Le Chatelier + Kc
Total questions: 31
Worksheet time: 16mins
Which statement is not correct about the industrial preparation of ethanol by the hydration of ethene at 300 °C?
C2H4(g) + H2O(g) ⇌ C2H5OH(g) ∆H = –46 kJ mol–1
The reaction is catalysed by an acid.
The higher the pressure, the higher the equilibrium yield of ethanol.
The higher the temperature, the higher the equilibrium yield of ethanol.
A low equilibrium yield of ethanol is acceptable because unreacted ethene is recycled.
For this reaction at equilibrium, which combination of temperature and pressure would give the greatest equilibrium yield of products?
W(g) + X(g) ⇌ 2Y(g) + Z(g) ∆H = +47 kJ mol–1
High pressure and high temperature
High pressure and low temperature
Low pressure and high temperature
Low pressure and low temperature
The forward reaction in this equilibrium is endothermic
COCl2 (g) ⇌ CO(g) + Cl2 (g)
Which statement is correct?
If the total pressure is increased at constant temperature, the proportion of COCl2 in the equilibrium mixture will decrease
Use of a catalyst will increase the proportion of COCl2 in the equilibrium mixture at constant temperature and pressure
Reducing the equilibrium concentration of CO will increase the value of the equilibrium constant
Raising the temperature from 373 K to 473 K will increase the value of the equilibrium constant
The following equilibrium was established in a container with volume V cm3 at 393 K and 200 kPa.
M2(g) + R(g) ⇌ RM2(g) ΔH = +150 kJ mol−1
Which change would increase the yield of RM2?
change the pressure to 150 kPa
change the temperature to 293 K
remove RM2 as it is formed
change the volume of the vessel to 2V cm3
A pale brown mixture of NO2 and N2O4 is allowed to reach equilibrium in a sealed gas syringe according to the following equation.
2NO2(g) ⇌ N2O4(g)
When the plunger is pushed further into the syringe the pressure increases and the mixture becomes paler in colour.
When the syringe is placed in a hot oven the mixture becomes darker in colour.
Which of the following statements is correct?
NO2 is brown and the forward reaction is exothermic.
NO2 is brown and the forward reaction is endothermic.
NO2 is colourless and the forward reaction is exothermic.
NO2 is colourless and the forward reaction is endothermic.
Hydrogen is produced by the reaction of methane with steam. The reaction mixture reaches a state of dynamic equilibrium.
CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g) ∆H = +206 kJ mol−1
Which of the following shows how the equilibrium yield of hydrogen and the value of the equilibrium constant are affected by the changes shown?
A
B
C
D
The standard enthalpy of formation, ΔHf for O3(g) is + 142 kJ mol–1. In which one of the following would both the changes shown increase the amount of O2 gas in an equilibrium mixture containing only O2(g) and O3(g)?
increasing the temperature and increasing the pressure
increasing the temperature and decreasing the pressure
decreasing the temperature and increasing the pressure
decreasing the temperature and decreasing the pressure
Use the information about the following solutions to answer the question below.
Solution F: This is a mixture of 1 mol of propanoic acid, 1 mol of methanol and 2 mol of water.
Solution G: This was originally the same mixture as solution F but it has been left to reach equilibrium.
Compared to the pH of solution F, the pH of solution G will be
considerably lower.
slightly lower.
slightly higher.
exactly the same.
Refer to the following reaction
H2(g) + I2(g) ⇌ 2HI(g) ΔH = −11 kJ mol−1, ΔS = +20 J K−1 mol−1
Which one of the following statements is correct?
This is a redox reaction.
The reaction is not feasible below 298 K
At equilibrium, the yield of hydrogen iodide is changed by increasing the pressure.
At equilibrium, the yield of hydrogen iodide increases as the temperature is increased.
The data below refer to the industrial production of nitric acid from ammonia.
The equilibrium yield in all three reactions is increased when
the pressure is increased.
the pressure is decreased.
the temperature is increased.
the temperature is decreased.
The ester methyl ethanoate is hydrolysed as shown in the following equation.
The equilibrium yield of ethanoic acid could be increased by
lowering the temperature.
adding a catalyst.
adding more water to the reaction mixture.
adding more methanol to the reaction mixture.
The following information concerns the equilibrium gas-phase synthesis of methanol.
CO(g) + 2H2(g) ⇌ CH3OH(g)
At equilibrium, when the temperature is 68 °C, the total pressure is 1.70 MPa.
The number of moles of CO, H2 and CH3OH present are 0.160, 0.320 and 0.180, respectively.
Thermodynamic data are given in the table.
Which one of the following statements applies to this equilibrium?
The value of Kp increases if the temperature is raised.
The value of Kp increases if the pressure is raised.
The yield of methanol decreases if the temperature is lowered.
The yield of methanol decreases if the pressure is lowered.
Normal water and heavy water react together to form isotopically mixed water according to the equation
H2O(l) + D2O(l) ⇌ 2HDO(l)
The standard enthalpy of formation of H2O(l) is −286 kJ mol−1, that of D2O(l) is −294 kJ mol−1, and that of HDO(l) is −290 kJ mol−1. Which one of the following best represents the variation with temperature of the yield of HDO at equilibrium?
The equilibrium constant, Kc, for a reaction which leads to ozone (O3) formation is given in the image.
More ozone is formed as the temperature rises. Which one of the following is true at equilibrium?
When ozone molecules collide with nitrogen they may form nitrogen monoxide.
The enthalpy change for the reaction has a negative sign.
Less ozone is formed at high pressure.
At a fixed temperature, the magnitude of Kc increases as the concentration of NO decreases.
Phosphorus(V) chloride decomposes at high temperatures into phosphorus(III) chloride and chlorine according to the equation.
PCl5(g) ⇌ PCl3(g) + Cl2(g)
Which one of the graphs best represents the variation with pressure of the yield of chlorine at equilibrium?
The graph shows the equilibrium percentage of ammonia present during the formation of ammonia by the Haber process:
N2 + 3H2 ⇌ 2NH3 ∆H = −92 kJ mol−1
Which one of the following are correct labels for the graph?
x axis: temperature Curve A: high pressure Curve B: low pressure
x axis: temperature Curve A: low pressure Curve B: high pressure
x axis: pressure Curve A: high temperature Curve B: low temperature
x axis: pressure Curve A: low temperature Curve B: high temperature
A weak acid HA dissociates in aqueous solution as shown below
HA(aq) ⇌ H+(aq) + A−(aq) ∆H = +20 kJ mol−1
Which one of the following changes will result in a decrease in the pH of an aqueous solution of the acid?
addition of a little aqueous sodium hydroxide solution
raising the temperature of the solution
dissolving a little of the sodium salt, NaA, in the solution
adding a platinum catalyst to the solution
A compound X is formed during a gas phase reaction. The graphs below show how the percentage of a compound X present at equilibrium varies with temperature and pressure.
Which one of the following statements concerning the formation of X is correct?
The reaction is exothermic and involves a decrease in the number of moles of gas.
The reaction is exothermic and involves no change in the number of moles of gas.
The reaction is exothermic and involves an increase in the number of moles of gas.
The reaction is endothermic and involves a decrease in the number of moles of gas.
A sample of chlorine gas was sealed in a tube, heated and an equilibrium was established.
Cl2(g) ⇌ 2Cl(g)
Which one of the following is not true?
The concentration of chlorine atoms remains the same when a catalyst is added to the tube.
Increase in temperature causes an increase in the concentration of chlorine atoms.
Increase in pressure causes an increase in the concentration of chlorine atoms relative to chlorine molecules.
Addition of more chlorine gas to the tube causes an increase in the concentration of chlorine atoms.
Hydrogen can be produced by this reaction.
CO(g) + H2O(g) ⇌ CO2(g) + H2(g)
In an experiment 4.20 mol of carbon monoxide were mixed with 2.00 mol of steam. When the reaction reached equilibrium, 1.60 mol of hydrogen had been formed.
What is the value of the equilibrium constant, Kc, for this reaction?
0.30
0.41
1.54
2.46
When one mole of ammonia is heated to a given temperature, 50% of the compound dissociates and the following equilibrium is established.
NH3(g) ⇌ 0.5N2(g) + 1.5H2(g)
What is the total number of moles of gas present in this equilibrium mixture?
1.5
2.0
2.5
3.0
A and B react together in this reversible reaction.
A + 3B ⇌ C + 2D
A mixture of 10 mol of A and 10 mol of B were left to reach equilibrium. The equilibrium mixture contained 4 mol of B.
What is the total amount, in moles, of substances in the equilibrium mixture?
14
16
18
20
Hydrogen is produced by the reaction of methane with steam. The reaction mixture reaches a state of dynamic equilibrium.
CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g) ∆H = +206 kJ mol−1
Which of the following shows how the equilibrium yield of hydrogen and the value of the equilibrium constant are affected by the changes shown?
Change: Increase pressure
Effect on equilibrium yield of H2(g): decrease
Effect on value of Kc: decrease
Change: Add a catalyst
Effect on equilibrium yield of H2(g): increase
Effect on value of Kc: no effect
Change: Increase temperature
Effect on equilibrium yield of H2(g): increase
Effect on value of Kc: increase
Change: Remove CO(g) as formed
Effect on equilibrium yield of H2(g): increase
Effect on value of Kc: increase
Use the information about the following solutions to answer the question below.
Solution F: This is a mixture of 1 mol of propanoic acid, 1 mol of methanol and 2 mol of water.
Solution G: This was originally the same mixture as solution F but it has been left to reach equilibrium.
Solution G was found to contain 0.5 mol of propanoic acid. Which one of the following is the value of the equilibrium constant (Kc) for the following equilibrium?
propanoic acid + methanol ⇌ methyl propanoate + water
0.2
1
5
10
Ethanoic acid reacts with ethanol in a reversible reaction represented by the equation below.
In an experiment 3.0 mol of ethanoic acid were mixed with 1.0 mol of ethanol and when the reaction had reached equilibrium 0.9 mol of water had been formed.
CH3COOH(l) + C2H5OH(l) ⇌ CH3COOC2H5(l) + H2O(l)
The equilibrium constant for the reaction under these conditions is
0.20
0.23
3.9
4.3
Ethanoic acid reacts with ethanol in a reversible reaction represented by the equation below.
In an experiment 3.0 mol of ethanoic acid were mixed with 1.0 mol of ethanol and when the reaction had reached equilibrium 0.9 mol of water had been formed.
CH3COOH(l) + C2H5OH(l) ⇌ CH3COOC2H5(l) + H2O(l)
The percentage of ethanoic acid converted into the ester CH3COOC2H5 in this reaction is
22.5%
30%
43%
90%
The data below refer to the industrial production of nitric acid from ammonia.
Possible units for the equilibrium constant, Kc, for reaction 2 are
mol−2 m6
mol−1 dm3
no units
mol dm−3
Use the information below to answer this question.
A saturated solution of magnesium hydroxide, Mg(OH)2, contains 0.1166 g of Mg(OH)2 in 10.00 dm3 of solution. In this solution the magnesium hydroxide is fully dissociated into ions.
The equilibrium constant expression for the dissolving of magnesium hydroxide is K = [Mg2+] [OH−]2. In a saturated solution of Mg(OH)2 at a different temperature, the concentration of hydroxide ions is 1.0 × 10−3 mol dm−3.
Which one of the following has the correct value and units for K under these conditions?
1.0 × 10−6 mol2 dm−6
5.0 × 10−7 mol2 dm−6
1.0 × 10−9 mol3 dm−9
5.0 × 10−10 mol3 dm−9
The ester methyl ethanoate is hydrolysed as shown in the following equation.
A 3 mol sample of methyl ethanoate was mixed with 3 mol of water and left to reach equilibrium at 298 K. The equilibrium yield of ethanoic acid was 2 mol. The value of Kc for this reaction at 298 K is
2
4
Methanol is synthesised from carbon monoxide and hydrogen according to the equation below.
CO(g) + 2H2(g)⇌ CH3OH(g) ∆H = −91 kJ mol−1
Which one of the following changes would not affect the value of the equilibrium constant and would not increase the yield of methanol?
increase in temperature
decrease in temperature
increase in pressure
decrease in pressure
The equilibrium constant, Kc, for a reaction which leads to ozone (O3) formation is shown in the image
More ozone is formed as the temperature rises. Which one of the following is true at equilibrium?
When ozone molecules collide with nitrogen they may form nitrogen monoxide.
The enthalpy change for the reaction has a negative sign.
Less ozone is formed at high pressure.
At a fixed temperature, the magnitude of Kc increases as the concentration of NO decreases.
