8.2. Effect of temperature on reaction rates and the concept of activation energy
A subsection of Chemistry, 9701, through 8. Reaction kinetics
Listing 10 of 111 questions
A chemist puts a sample of dilute aqueous hydrochloric acid into beaker 1. She adds a sample of zinc and measures the rate of production of hydrogen gas. She then puts a different sample of dilute aqueous hydrochloric acid into beaker 2. She adds a different sample of zinc and measures the rate of production of hydrogen gas. The rate of the reaction in beaker 2 is greater than the rate of the reaction in beaker 1. Which factors could help to explain this observation?
9701_m16_qp_12
MCQ
2016
Paper 1, Variant 2
View
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
View
The initial rate of reaction for propanone and iodine in acid solution is measured in a series of experiments at a constant temperature. H+ catalyst CH3COCH3 + I2 CH3COCH2I + HI The rate equation was determined experimentally to be as shown. rate = k [H+] State the order of reaction with respect to ● CH3COCH3 ● I2 ● H+ and state the overall order of this reaction.  The rate of this reaction is 5.40 × 10–3 mol dm–3 s–1 when ● the concentration of CH3COCH3 is 1.50 × 10–2 mol dm–3 ● the concentration of I2 is 1.25 × 10–2 mol dm–3 ● the concentration of H+ is 7.75 × 10–1 mol dm–3. Calculate the rate constant, k, for this reaction. State the units of k.  k =  units =  Complete the table by placing one tick () in each row to describe the effect of decreasing the temperature on the rate constant and on the rate of reaction. decreases no change increases rate constant rate of reaction  From the results, a graph is produced which shows how the concentration of I2 changes during the reaction. time Describe how this graph could be used to determine the initial rate of the reaction. On the axes below, sketch a graph to show how the initial rate changes with different initial concentrations of CH3COCH3 in this reaction. rate  The rate of a reaction between metal ions was studied. The following three-step mechanism has been suggested for this reaction. Step1 is the rate-determining step. step 1 Ce4+ + Mn2+ Ce3+ + Mn3+ step 2 Ce4+ + Mn3+ Ce3+ + Mn4+ step 3 Mn4+ + Tl + Tl 3+ + Mn2+ Explain the meaning of the term rate-determining step. Use this mechanism to ● determine the overall equation for this reaction ● suggest the role of Mn2+ ions in this mechanism. Explain your answer.  
9701_s19_qp_42
THEORY
2019
Paper 4, Variant 2
View
Questions Discovered
111