8. Reaction kinetics
A section of Chemistry, 9701
Listing 10 of 220 questions
Sulfur trioxide, SO3, is manufactured from sulfur dioxide and oxygen by the Contact process. 2SO2+ O22SO3ΔH = –196.0 kJ mol–1 The enthalpy change of formation of SO2, ΔHf SO2, is –296.8 kJ mol–1. Define the term enthalpy change of formation. Use the data to calculate the enthalpy change of formation of SO3. ΔHf SO3= kJ mol–1 The Contact process is usually carried out at a temperature of approximately 700 K, a pressure of approximately 150 kPa and in the presence of a vanadium(oxide catalyst, V2O5. The Boltzmann distribution for a mixture of SO2 and O2 at 700 K is shown. Eacat represents the activation energy for the reaction in the presence of the catalyst. proportion of molecules with a given energy molecular energy Eacat Add a labelled mark, Eauncat, to the diagram to indicate the activation energy in the absence of the catalyst. State the benefit of using a catalyst in this reaction. Explain how it achieves this effect. State and explain how an increase in pressure would affect both the rate of reaction and the yield of SO3 in the Contact process. rate yield At a pressure of 1.50 × 105 Pa, 1.00 mol of sulfur dioxide gas, SO2, was mixed with 1.00 mol of oxygen gas, O2. The final equilibrium mixture formed was found to contain 0.505 mol of O2. 2SO2+ O22SO3Calculate the amount, in mol, of SO2 and SO3 in the equilibrium mixture. SO2 = mol SO3 = mol Calculate the partial pressure of oxygen gas, pO2, in the equilibrium mixture. pO2 = Pa In another equilibrium mixture formed from different starting amounts of SO2 and O2, the partial pressures of SO2, O2 and SO3 were as shown. pSO2 = 8.42 × 102 Pa pO2 = 6.00 × 104 Pa pSO3 = 9.10 × 104 Pa Write the expression for the equilibrium constant, Kp, for the production of SO3 from SO2 and O2. Kp = Calculate the value of Kp for this reaction and state the units. Kp = units =
9701_s17_qp_23
THEORY
2017
Paper 2, Variant 3
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The spontaneity of a chemical reaction depends on the standard Gibbs free energy change, ∆G o. This is related to the standard enthalpy and entropy changes by the equation shown. ∆G o = ∆H o – T∆S o State and explain whether the following processes will lead to an increase or decrease in entropy. the reaction of magnesium with hydrochloric acid entropy change explanation solid potassium chloride dissolving in water entropy change explanation steam condensing to water entropy change explanation Magnesium carbonate can be decomposed. MgCO3→ MgO+ CO2∆H o = +117 kJ mol–1 Standard entropies are shown in the table. substance MgCO3MgOCO2S o / J mol–1 K–1 +65.7 +26.9 +214 Calculate ∆G o for this reaction at 298 K. Include a relevant sign and give your answer to three significant figures. ∆G o = kJ mol–1 Explain, with reference to ∆G o, why this reaction becomes more feasible at higher temperatures. On heating, sodium hydrogencarbonate decomposes into sodium carbonate as shown. 2NaHCO3→ Na2CO3+ CO2+ H2O∆H o = +130 kJ mol–1 ∆S o = +316 J mol–1 K–1 Calculate the minimum temperature at which this reaction becomes spontaneous . Show your working. temperature = K The solubility of Group 2 sulfates decreases down the Group. Explain this trend.
9701_w16_qp_41
THEORY
2016
Paper 4, Variant 1
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The spontaneity of a chemical reaction depends on the standard Gibbs free energy change, ∆G o. This is related to the standard enthalpy and entropy changes by the equation shown. ∆G o = ∆H o – T∆S o State and explain whether the following processes will lead to an increase or decrease in entropy. the reaction of magnesium with hydrochloric acid entropy change explanation solid potassium chloride dissolving in water entropy change explanation steam condensing to water entropy change explanation Magnesium carbonate can be decomposed. MgCO3→ MgO+ CO2∆H o = +117 kJ mol–1 Standard entropies are shown in the table. substance MgCO3MgOCO2S o / J mol–1 K–1 +65.7 +26.9 +214 Calculate ∆G o for this reaction at 298 K. Include a relevant sign and give your answer to three significant figures. ∆G o = kJ mol–1 Explain, with reference to ∆G o, why this reaction becomes more feasible at higher temperatures. On heating, sodium hydrogencarbonate decomposes into sodium carbonate as shown. 2NaHCO3→ Na2CO3+ CO2+ H2O∆H o = +130 kJ mol–1 ∆S o = +316 J mol–1 K–1 Calculate the minimum temperature at which this reaction becomes spontaneous . Show your working. temperature = K The solubility of Group 2 sulfates decreases down the Group. Explain this trend.
9701_w16_qp_43
THEORY
2016
Paper 4, Variant 3
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Questions Discovered
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