Reactivity 2: How much, how fast and how far?IB Chemistry HL: Topic test

20 questions, 54 marks

IB Chemistry HL

Reactivity 2: How much, how fast and how far? topic test

Total 54 marks

Name

Class

Date

1
50.0 cm\u00b3 of 0.200 mol dm\u207b\u00b3 barium chloride solution is mixed with 40.0 cm\u00b3 of 0.150 mol dm\u207b\u00b3 sodium sulfate solution: BaCl\u2082(aq) + Na\u2082SO\u2084(aq) \u2192 BaSO\u2084(s) + 2NaCl(aq). The mixture is filtered and the solid barium sulfate is dried and weighed; the dry mass obtained is 1.24 g.
(a)
Which reactant is limiting?
[1 mark]
ASodium sulfate, because only 0.0060 mol is present compared with 0.0100 mol of barium chloride
BBarium chloride, because it has the higher concentration
CNeither — the reactants are present in the exact 1:1 stoichiometric ratio
DIt cannot be determined without knowing the mass of precipitate formed
(b)
What is the theoretical (maximum possible) mass of barium sulfate that could form (Mr BaSO₄ = 233.4)?
[1 mark]
A2.33 g
B1.40 g
C0.86 g
D1.75 g
(c)
Calculate the percentage yield of barium sulfate obtained.
[2 marks]
Total for question 1: 4 marks
2
A chemist studies the decomposition of hydrogen peroxide catalysed by manganese(IV) oxide: 2H\u2082O\u2082(aq) \u2192 2H\u2082O(l) + O\u2082(g). At 20 \u00b0C the reaction is slow, but raising the temperature to 40 \u00b0C approximately doubles the initial rate. Adding solid MnO\u2082 increases the rate further without being consumed.
(a)
Why does raising the temperature from 20 °C to 40 °C increase the initial rate of decomposition?
[1 mark]
AThe activation energy of the reaction decreases at higher temperature
BMore particles are present in the same volume, increasing the collision frequency
CA greater fraction of particles have kinetic energy ≥ the activation energy, so more collisions are successful
DThe particles collide with a more favourable orientation at higher temperature
(b)
What effect does adding solid MnO₂ have on the activation energy and the enthalpy change of the reaction?
[1 mark]
ABoth the activation energy and the enthalpy change decrease
BThe activation energy increases; the enthalpy change is unchanged
CThe activation energy is unchanged; the enthalpy change decreases
DThe activation energy decreases; the enthalpy change is unchanged
(c)
Describe how the Maxwell–Boltzmann energy distribution at 40 °C compares with that at 20 °C, and explain how this accounts for the higher rate.
[2 marks]
Total for question 2: 4 marks
3
Nitric acid is manufactured by oxidising ammonia: 4NH\u2083(g) + 5O\u2082(g) \u2192 4NO(g) + 6H\u2082O(g). In a trial run, 340 kg of ammonia (Mr 17.0) reacts with excess oxygen. The actual yield of NO obtained is 92.0% of the theoretical maximum.
(a)
Calculate the atom economy of this reaction, treating NO as the only desired product.
[3 marks]
(b)
Calculate the mass of NO actually obtained from 340 kg of ammonia, given the 92.0% actual yield.
[4 marks]
Total for question 3: 7 marks
4
Industrial methanol synthesis uses the reaction CO(g) + 2H\u2082(g) \u21cc CH\u2083OH(g), \u0394H = \u221291 kJ mol\u207b\u00b9, carried out at about 250 \u00b0C and 100 atm over a Cu/ZnO/Al\u2082O\u2083 catalyst, even though a lower temperature would give a higher equilibrium yield of methanol.
(a)
Using ideas of rate and equilibrium, explain why a moderate temperature of about 250 °C is used industrially rather than either a very low or a very high temperature.
[6 marks]
(b)
The pressure used is 100 atm, much higher than atmospheric pressure. Evaluate, using Le Chatelier's principle and practical considerations, whether operating at an even higher pressure (e.g. 250 atm) would be worthwhile.
[6 marks]
Total for question 4: 12 marks
5
Sulfur dioxide is oxidised to sulfur trioxide in the Contact process: 2SO\u2082(g) + O\u2082(g) \u21cc 2SO\u2083(g), \u0394H = \u2212196 kJ mol\u207b\u00b9. At 450 \u00b0C the reaction reaches equilibrium in a sealed vessel at constant volume.
(a)
What is the correct expression for Kc for this equilibrium?
[1 mark]
AKc = [SO₃]² / ([SO₂]²[O₂])
BKc = [SO₂]²[O₂] / [SO₃]²
CKc = [SO₃] / ([SO₂][O₂])
DKc = [SO₂][O₂] / [SO₃]
(b)
Predict the effect on the equilibrium position and on Kc of increasing the pressure on the system at constant temperature.
[1 mark]
AEquilibrium shifts left (towards SO₂ and O₂); Kc increases
BEquilibrium shifts right (towards SO₃); Kc is unchanged
CEquilibrium shifts right (towards SO₃); Kc increases
DNo shift in equilibrium position; Kc decreases
(c)
State and explain the effect of increasing temperature at constant pressure on the position of this equilibrium.
[2 marks]
Total for question 5: 4 marks
6
The reaction between bromate(V) ions and bromide ions in acidic solution was studied: BrO\u2083\u207b(aq) + 5Br\u207b(aq) + 6H\u207a(aq) \u2192 3Br\u2082(l) + 3H\u2082O(l). Three experiments at the same temperature gave: Experiment 1: [BrO\u2083\u207b] = 0.10 mol dm\u207b\u00b3, [Br\u207b] = 0.10 mol dm\u207b\u00b3, [H\u207a] = 0.10 mol dm\u207b\u00b3, rate = 1.2 \u00d7 10\u207b\u00b3 mol dm\u207b\u00b3 s\u207b\u00b9. Experiment 2: [BrO\u2083\u207b] = 0.20 mol dm\u207b\u00b3, others unchanged, rate = 2.4 \u00d7 10\u207b\u00b3 mol dm\u207b\u00b3 s\u207b\u00b9. Experiment 3: [H\u207a] = 0.20 mol dm\u207b\u00b3, others as experiment 1, rate = 4.8 \u00d7 10\u207b\u00b3 mol dm\u207b\u00b3 s\u207b\u00b9.
(a)
What is the order of reaction with respect to BrO₃⁻?
[1 mark]
AZero order
BThe order cannot be determined from this data
CFirst order
DSecond order
(b)
What is the order of reaction with respect to H⁺?
[1 mark]
AZero order
BFirst order
CThe order cannot be determined from this data
DSecond order
(c)
Given that the reaction is also first order with respect to Br⁻, use experiment 1 to calculate the rate constant, k, including its units.
[2 marks]
Total for question 6: 4 marks
7
At 500 K, Kc for N\u2082(g) + 3H\u2082(g) \u21cc 2NH\u2083(g) is 1.7 \u00d7 10\u207b\u00b2 mol\u207b\u00b2 dm\u2076. A 2.00 dm\u00b3 vessel at 500 K contains 0.40 mol N\u2082, 0.90 mol H\u2082 and 0.10 mol NH\u2083, not yet at equilibrium.
(a)
Calculate the reaction quotient, Q, for this mixture, and use it to determine the direction in which the reaction will proceed to reach equilibrium.
[3 marks]
(b)
Given ΔG⊖ = −RT ln K (R = 8.31 J K⁻¹ mol⁻¹), calculate ΔG⊖ for this reaction at 500 K, and state what the sign of ΔG⊖ indicates about the position of equilibrium relative to standard conditions.
[4 marks]
Total for question 7: 7 marks
8
A company makes ethyl ethanoate by esterification: CH\u2083COOH(l) + C\u2082H\u2085OH(l) \u21cc CH\u2083COOC\u2082H\u2085(l) + H\u2082O(l), Kc \u2248 4 at room temperature. The uncatalysed reaction is very slow at room temperature.
(a)
The company adds a small amount of concentrated sulfuric acid to the mixture and gently heats it. Explain, in terms of rate and mechanism ideas, why this increases how quickly the mixture reaches equilibrium, and explain why adding the acid catalyst does not change the equilibrium yield of ethyl ethanoate.
[6 marks]
(b)
Kc for this reaction is about 4 at room temperature. Starting from 1.00 mol of ethanoic acid and 1.00 mol of ethanol with no products present, evaluate whether removing the water formed (e.g. using a drying agent) as the reaction proceeds would be an effective way to increase the percentage yield of ethyl ethanoate, using Le Chatelier's principle and the equilibrium law.
[6 marks]
Total for question 8: 12 marks

End of questions