Unit 5: Reactivity 2: How Much, How Fast and How Far?
Topic 5.3: How Far? The Extent of Chemical Change Questions
Practice 8 exam-style questions for IB Chemistry Topic 5.3. Review the question stems below, then unlock the full Question Bank to access markschemes, model answers, and AI grading.
1State1 mark
• Aimnova practice
Write the equilibrium constant expression, Kc, for the equilibrium 2NO(g) + O2(g) ⇌ 2NO2(g).
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Unlock Question2State2 marks
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A reversible reaction is left in a sealed flask at constant temperature until no further change is observed.
State two features of a system that has reached dynamic equilibrium. [2]
State two features of a system that has reached dynamic equilibrium. [2]
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Unlock Question3Explain3 marks
• Aimnova practice
Hydrogen and iodine reach equilibrium in a sealed container: H2(g) + I2(g) ⇌ 2HI(g), where I2 vapour is purple.
Explain why the colour of the mixture becomes constant once equilibrium is reached, even though the reaction has not stopped. [3]
Explain why the colour of the mixture becomes constant once equilibrium is reached, even though the reaction has not stopped. [3]
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Unlock Question4Calculate3 marks
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At a certain temperature, 1.0 mol of N2O4 is placed in a 2.0 dm³ flask and allowed to reach the equilibrium N2O4(g) ⇌ 2NO2(g).
At equilibrium 0.60 mol of N2O4 remains.
Calculate the value of Kc for this equilibrium. [3]
At equilibrium 0.60 mol of N2O4 remains.
Calculate the value of Kc for this equilibrium. [3]
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Unlock Question5Calculate3 marks
• Aimnova practice
Hydrogen and iodine react in a sealed 1.00 dm³ flask: H2(g) + I2(g) ⇌ 2HI(g).
Initially 2.00 mol of H2 and 2.00 mol of I2 are present, and at equilibrium 3.00 mol of HI has formed.
Calculate Kc.
Initially 2.00 mol of H2 and 2.00 mol of I2 are present, and at equilibrium 3.00 mol of HI has formed.
Calculate Kc.
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Unlock Question6Predict3 marks
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Methanol is made industrially by CO(g) + 2H2(g) ⇌ CH3OH(g), which is exothermic in the forward direction.
Predict, with a reason, the effect of (i) increasing the pressure and (ii) raising the temperature on the equilibrium yield of methanol. [3]
Predict, with a reason, the effect of (i) increasing the pressure and (ii) raising the temperature on the equilibrium yield of methanol. [3]
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Unlock Question7Calculate3 marks
• Aimnova practice
A gas-phase reaction has an equilibrium constant K = 0.020 at 500 K.
Calculate its standard Gibbs energy change, ΔG°, in kJ mol⁻¹, and state whether the reaction is spontaneous.
(R = 8.31 J K⁻¹ mol⁻¹.)
Calculate its standard Gibbs energy change, ΔG°, in kJ mol⁻¹, and state whether the reaction is spontaneous.
(R = 8.31 J K⁻¹ mol⁻¹.)
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Unlock Question8Deduce3 marks
• Aimnova practice
A sealed flask contains the equilibrium 2NO2(g) ⇌ N2O4(g), where brown NO2 forms colourless N2O4.
Cooling the flask makes the mixture turn paler.
Deduce, with a reason, whether the forward reaction is exothermic or endothermic, and state the effect of cooling on Kc. [3]
Cooling the flask makes the mixture turn paler.
Deduce, with a reason, whether the forward reaction is exothermic or endothermic, and state the effect of cooling on Kc. [3]
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