Factors affecting the rate of reaction

This question is about rates of reaction.

The rate of hydrolysis of a bromoalkane (RBr) is investigated using this method.

• A boiling tube has a cross drawn onto it.

• An aqueous solution of silver nitrate is added to an ethanolic solution of RBr in the boiling tube in a warm water bath.

• The time is recorded for the cross on the boiling tube to become invisible.

The method is repeated at different temperatures.

State why the cross on the boiling tube becomes invisible.

The volume and concentration of each substance used at each temperature is kept constant.

Identify one other variable that should be kept constant to ensure that the investigation is fair.

The reaction between the bromoalkane RBr and an aqueous solution of KOH is investigated.

The rate constant k for this reaction is determined at a series of temperatures T.

The Arrhenius equation can be written in this form.

Table 2 shows an incomplete set of results for this investigation.

Complete Table 2.

The results in Table 2 can be used to plot a graph to determine the activation energy E_a for this reaction.

Complete the x-axis in Figure 10 by adding an appropriate scale.

Plot the graph on the grid in Figure 10.

Use your graph to determine a value, in kJ mol^–1, for the activation energy E_a

The gas constant, R = 8.31 J K^–1 mol^–1

The rate equation for the reaction between a different bromoalkane (R₂CHBr) and an aqueous solution of KOH is

Which of these is a correct mechanism for the reaction between R₂CHBr and KOH?

Tick (✓) one box.

Explain, in terms of bond polarity, why R₂CHBr and KOH react together.

50.0 cm³ of 0.015 mol dm^–3 Fe₂(SO₄)₃(aq) are mixed with 50.0 cm³ of

The mixture is left for several hours until equilibrium is reached.

A sample of the equilibrium mixture is titrated to determine the amount of I^–(aq) in the equilibrium mixture.

Give the expression for the equilibrium constant, K_c, for the equilibrium.

Before the titration, the sample is ‘quenched’ by adding 50 cm³ of ice-cold water.

Suggest why the sample is ‘quenched’ in this way before the titration. Explain your answer.

The amount of I^–(aq) in the equilibrium mixture is found to be 3.00 × 10^–4 mol

Calculate the value of K_c at 40 °C for the equilibrium.

Assume that the total volume of the mixture remains constant at 100 cm³

This question is about ethanoic anhydride.

In the gas phase, ethanoic anhydride (CH₃CO)₂O decomposes to form ethenone.

The equation is

Ethenone is the simplest member of the ketene homologous series. Ketenes all contain one C=C double bond and one C=O double bond.

Deduce the general formula for the ketene homologous series.

Figure 11 shows an incomplete suggested mechanism for the decomposition of ethanoic anhydride.

Complete the mechanism in Figure 11 by adding three curly arrows and any relevant lone pairs of electrons.

For a chemical reaction the relationship between the rate constant, k, and the temperature, T, is shown by the Arrhenius equation.

For the decomposition of gaseous ethanoic anhydride

the activation energy, E_a = 34.5 kJ mol^–1

At temperature T₁ the rate constant, k = 2.48 10⁸ s^–1

The gas constant, R = 8.31 J K^–1 mol^–1

Sketch the Maxwell–Boltzmann distribution of molecular energies for gaseous ethanoic anhydride at temperature T₁ and at a higher temperature T₂

Include a label for each axis, and mark on the appropriate axis a typical position for the activation energy.

Explain why the rate of reaction is faster at T₂

Explanation

An acidified solution of butanone reacts with iodine as shown.

Draw the displayed formula for CH₃CH₂COCH₂I

Give the name of CH₃CH₂COCH₂I

Displayed formula

The rate equation for the reaction is

Table 1 shows the initial concentrations used in an experiment.

The initial rate of reaction in this experiment is 1.45×10⁻⁴ mol dm⁻³ s⁻¹

Calculate the value of the rate constant, k, for the reaction and give its units.

Calculate the initial rate of reaction when all of the initial concentrations are halved.

An experiment was done to measure the time, t, taken for a solution of iodine to react completely when added to an excess of an acidified solution of butanone.

Suggest an observation used to judge when all the iodine had reacted.

The experiment was repeated at different temperatures. Figure 1 shows how varied with temperature for these experiments.

Describe and explain the shape of the graph in Figure 1.

Deduce the time taken for the reaction at 35^oC

For a different reaction, Table 2 shows the value of the rate constant at different temperatures.

This equation can be used to calculate the activation energy, E_a

Calculate the value, in kJ mol⁻¹, of the activation energy, E_a

The gas constant, R = 8.31 J K⁻¹mol⁻¹

Name and outline the mechanism for the reaction of butanone with KCN followed by dilute acid.

Name of mechanism

Outline of mechanism

Hydrogen peroxide solution decomposes to form water and oxygen.

The reaction is catalysed by manganese(IV) oxide.

A student determines the order of this reaction with respect to hydrogen peroxide. The student uses a continuous monitoring method in the experiment.

The student places hydrogen peroxide solution in a conical flask with the catalyst and uses a gas syringe to collect the oxygen formed. The student records the volume of oxygen every 10 seconds for 100 seconds.

Explain why the reaction is fastest at the start.

The graph in Figure 1 shows how the concentration of hydrogen peroxide changes with time in this experiment.

Tangents to the curve in Figure 1 can be used to determine rates of reaction.

Draw a tangent to the curve when the concentration of hydrogen peroxide solution is

Use your tangent to calculate the gradient of the curve at this point.

The concentration of hydrogen peroxide solution at time t during the experiment can be calculated using this expression.

H₂O_2t = concentration of hydrogen peroxide solution at time t / mol dm_–3

H₂O_2initial = concentration of hydrogen peroxide solution at the start / mol dm_–3

V_max = total volume of oxygen gas collected during the whole experiment / cm³

V_t = volume of oxygen gas collected at time t / cm³

Use Figure 1 and the expression to calculate H₂O_2t when 20 cm₃ of oxygen has been collected.

Table 5 shows data from a similar experiment.

Plot the data from Table 5 on the grid in Figure 2.

Draw a line of best fit.

Use Figure 2 to determine the order of reaction with respect to H₂O₂

State how the graph shows this order.

How the graph shows this order

Sodium thiosulfate reacts with dilute hydrochloric acid as shown.

Give the simplest ionic equation for this reaction.

The gas SO₂ is a pollutant.

State the property of SO₂ that causes pollution when it enters rivers.

Give an equation to show the reaction of SO₂ with water.

Draw a diagram to show the shape of a molecule of H₂O Include any lone pairs of electrons.

State the HOH bond angle.

Explain this shape and bond angle.

Diagram

The initial rate of the reaction between sodium thiosulfate and hydrochloric acid can be monitored by measuring the time taken for a fixed amount of sulfur to be produced.

Describe an experiment to investigate the effect of temperature on the initial rate of this reaction.

Include

• a brief outline of your method

• how you will measure the time taken for a fixed amount of sulfur to be formed

• how you will present your results in graphical form

• a sketch of the graph that you would expect.