3.2 Rates of Reaction

Dilute hydrochloric acid reacts with a solution of sodium thiosulfate (Na₂S₂O₃) to form a precipitate.

The equation for the reaction is

Na₂S₂O₃ (aq) + 2HCl (aq) → 2NaCl (aq) + S (s) + H₂O (l) + SO₂ (g)

State the name of the precipitate that forms.

• Pour 50 cm³ of cold sodium thiosulfate solution into a conical flask and heat it to 20 °C
• Draw a cross (X) on a piece of paper and place it under the flask
• Add 5 cm³ of dilute hydrochloric acid to the flask
• Look at the cross from above and record the time taken until the cross cannot be seen

The table shows the student’s results.

The highest temperature the student uses is 60 °C because he thinks the results might not be as accurate at temperatures higher than 60 °C.

Suggest a reason why the results might not be as accurate at temperatures higher than 60 °C.

The student wants to compare the rates of the reaction at the different temperatures.

He uses this formula to obtain a value for each rate of reaction

rate = 

The table shows the value of the rate of reaction at each temperature.

A student uses this apparatus to investigate the rate of reaction between marble chips and dilute hydrochloric acid.

The equation for the reaction is

CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂

During the reaction the mass of the contents of the flask decreases.

The graph shows the student’s results.

Explain, using particle collision theory, how increasing the temperature affects the rate of a reaction.

This question is about reactions that form gases.

Hydrogen peroxide decomposes to form water and oxygen.

The equation for the reaction is

2H₂O₂ → 2H₂O + O₂

25.0 cm³ of hydrogen peroxide solution are poured into a conical flask and 1.00 g of solid manganese(IV) oxide is added.

Bubbles of oxygen gas are formed.

(1)

(3)

A student uses this apparatus to investigate the rate of the reaction between zinc and an excess of dilute hydrochloric acid.

This is the student’s method.

• pour 50 cm³ of dilute hydrochloric acid into a conical flask
• add about 1.2 g of zinc lumps
• record the volume of hydrogen gas collected every 30 s until no more hydrogen is collected

The graph shows the student’s results.

(2)

mean rate = .............................................................. cm³ / s

(3)

(2)

(2)

In another experiment, the student adds 0.55 g of zinc to a solution containing 2.50 × 10⁻² moles of hydrochloric acid.

Use the equation to show that hydrochloric acid is in excess.

[A_r of Zn = 65]

A student uses this apparatus to investigate the rate of reaction between calcium carbonate chips and dilute hydrochloric acid.

Every 20 seconds the student records the reading on the balance.

Explain why using a cotton wool plug increases the accuracy of the student’s results.

Complete the equation for the reaction by adding the state symbols.

The student uses the balance readings to find the decrease in mass of the flask and contents.

The graph shows the student’s results.

The student repeats the investigation by diluting the original hydrochloric acid. 

The student then determines the initial rate of reaction at different percentage concentrations of the original hydrochloric acid. 

The graph shows the student’s results.

A student uses this apparatus in an experiment to study the rate of the reaction between zinc and dilute sulfuric acid.

This is the student’s method.

• Add a few zinc granules to a conical flask on a balance
• Add 100 cm³ of dilute sulfuric acid to the flask, start a timer and immediately record the mass of the flask and contents
• Record the mass of the flask and contents every minute until the mass remains constant

The mass of the flask and contents decreases because hydrogen gas is produced and leaves the flask.

The student uses the mass readings to calculate the total mass of hydrogen produced.

Complete the equation for the reaction by adding the state symbols. 

The table shows the student’s results.

The student does another experiment using

• the same amount of similarly sized magnesium granules instead of zinc
• the same volume of sulfuric acid, but of a lower concentration

Explain why it is difficult to predict how the rate of reaction in this experiment compares with the rate of reaction in the first experiment.

Explain, in terms of particle collision theory, how increasing the temperature affects the rate of a reaction.

Hydrogen peroxide solution decomposes slowly at room temperature to form water and oxygen. The equation for the reaction is

2H₂O₂ → 2H₂O + O₂

A catalyst increases the rate of this reaction. State one other property of a catalyst.

A student has samples of three solids, X, Y and Z. The student uses this apparatus to find out which solids act as catalysts in the decomposition of hydrogen peroxide solution.

Describe the method that the student should use to find out which solids act as catalysts.

Separate: Chemistry Only

The decomposition of hydrogen peroxide solution is exothermic.

On the diagram, draw and label the reaction profiles for the reaction

• without a catalyst
• with a catalyst

Separate: Chemistry Only

The equation for the reaction can be shown using displayed formulae.

2H-O-O-H → 2H-O-H + O=O    ΔH = –204kJ

The table gives the bond energies for the two of the bonds

(1)

energy needed = .............................................................. kJ

(1)

energy released = .............................................................. kJ

(2)

bond energy = .............................................................. kJ/mol

A student uses this apparatus to investigate the rate of reaction between marble chips and dilute hydrochloric acid.

(2)

(1)

This is the equation for the reaction between marble chips and dilute hydrochloric acid.

Complete the equation by adding the state symbols.

CaCO₃ (.........) + 2HCl (.........) → CaCl₂ (.........) + H₂O (.........) + CO₂ (.........)

The student uses large marble chips in the investigation.

This is a graph of his results.

The student repeats the experiment using the same total mass of smaller marble chips.

On the graph, draw the curve that would be obtained.
[assume the marble chips are in excess]

The rate of this reaction can be altered by increasing the temperature or by increasing the concentration of the hydrochloric acid.

(3)

(3)

A solution of hydrogen peroxide decomposes when a catalyst of manganese(IV) oxide is added.

The products of the reaction are water and oxygen.

Complete the chemical equation for this reaction.

............ H₂O₂ → ........... H₂O + ........... O₂

State the reason for adding a catalyst.

A student investigates how changing the concentration of the hydrogen peroxide solution affects the rate of this reaction.

She uses this apparatus.

The student records the volume of oxygen that collects every 2 minutes for 16 minutes.

volume of oxygen = ............................................... cm³

The student repeats the experiment using hydrogen peroxide solution of half the concentration of the original solution. She keeps the volume of the hydrogen peroxide solution and all other conditions the same.

(2)

(3)

Zinc reacts with dilute hydrochloric acid to form hydrogen.

A student investigates the reaction between pieces of zinc and dilute hydrochloric acid.

In each experiment, he uses the same mass of zinc but a different volume of the acid.

He collects the hydrogen and measures its volume in each experiment.

The graph shows the student’s results.

Explain how increasing the concentration of the hydrochloric acid affects the rate of reaction.

The rate of reaction could also be affected by changing the temperature of the hydrochloric acid, or by using a catalyst. Explain one other way in which the rate of reaction between zinc and hydrochloric acid can be affected.

Hydrogen peroxide solution decomposes to give water and oxygen gas.

The equation for this reaction is:

2H₂O₂ (aq) → 2H₂O (l) + O₂ (g)

Three different solids are catalysts for the decomposition of hydrogen peroxide solution.

A student is given hydrogen peroxide solution and a sample of each of the solid catalysts.

The student has a timer, a measuring cylinder, a balance and the apparatus shown in the diagram.

Describe a method the student could use to find which of the three solids is the most effective catalyst for the decomposition of hydrogen peroxide solution.

The diagram shows the reaction profile for the decomposition of hydrogen peroxide without a catalyst.

Hydrogen peroxide, H₂O₂, quickly decomposes to produce water and oxygen when a catalyst is added to the solution:

2H₂O₂ (aq) → 2H₂O (l)  + O₂ (g)

The volume of gas produced was measured and is shown in the graph below:

Which statement is not true for this reaction?

This question is about ethane and ethene.

Ethane can be obtained from crude oil.

Describe the industrial process used to separate crude oil into fractions.

Separate: Chemistry Only

The equation for the reaction between ethene gas and hydrogen gas is

C₂H₄ + H₂ →  C₂H₆

(2)

(2)

(1)

Separate: Chemistry Only

The reaction between ethene and hydrogen can be represented using displayed formulae.

Use the bond energies in the table to calculate the enthalpy change, ΔH, in kJ/mol for this reaction.

ΔH = .............................................................. kJ/mol