7.1 Rates of Reaction

This question is about rates of reaction.

A student investigates the effect of catalysts on the rate of reaction between iron(III) nitrate solution and sodium thiosulfate solution using this method.

• transfer 50 cm³ of iron(III) nitrate solution into a conical flask
• add 1 cm³ of catalyst
• transfer 50 cm³ of sodium thiosulfate solution into the conical flask
• record the time taken for the mixture to become colourless

Explain how a catalyst increases the rate of reaction.

Figure 1 shows the student's results repeating the experiment using different catalysts and also with no catalyst.

Figure 1

Explain which is the best catalyst for the reaction.

Explain, using particle collision theory, how using a solution of a lower concentration affects the rate of reaction.

The rate of a reaction can also be altered by changing other factors.

Explain one factor that will not affect the rate of reaction.

A student uses the apparatus in Figure 1 to investigate the rate of reaction between calcium carbonate chips and dilute hydrochloric acid.

Figure 1

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.

Higher Only

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

The graph in Figure 2 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 in Figure 3 shows the student’s results.

A student uses this apparatus to investigate the rate of reaction between magnesium and an excess of dilute hydrochloric acid. The apparatus is shown in Figure 1.

Figure 1

She uses this method.

• use a graduated beaker to pour 50 cm³ of dilute hydrochloric acid of concentration 2.00 mol / dm³ into the conical flask
• add a piece of magnesium ribbon of mass 0.086 g to the acid and put the bung into the neck of the flask
• measure the total volume of gas collected every ten seconds until the reaction stops

The table shows the student's results in Figure 2.

 Figure 2

• 0.043 g of magnesium ribbon
• 50 cm³ of 2.00 mol / dm³ hydrochloric acid

• 0.086 g of magnesium ribbon
• 50 cm³ of 2.00 mol / dm³ hydrochloric acid
• a slightly higher temperature than the first experiment

The expected volume of gas produced in the first experiment is 86 cm³.

Suggest why the volume collected is less than the expected volume.

The student uses a graduated beaker to measure the volume of dilute hydrochloric acid.

Explain why it is not necessary to use a measuring cylinder in this experiment.

The ionic equation for the reaction between magnesium and hydrochloric acid is

Mg (s) + 2H⁺ (aq) → Mg²⁺ (aq) + H₂ (g)

Use the information in this equation, and the particle collision theory, to explain why the rate of reaction decreases during each of the experiments.

Figure 1 shows a diagram of the apparatus which could be used to investigate the rate of reaction between magnesium and an excess of an acid is drawn below.

Figure 1

The magnesium kept rising to the surface. In one experiment, this was prevented by twisting the magnesium around a piece of copper. In a second experiment, the magnesium was held down by a plastic net fastened to the beaker.

(1)

(1)

The only difference between the two experiments was the method used to hold down the magnesium. The results are shown below in Figure 2.

(1)

(1)

Higher Only

The experiment was repeated using propanoic acid instead of hydrochloric acid. Propanoic acid is a weak acid.

(1)

(1)

The rate of a reaction can also be altered by changing the temperature or by changing the surface area.

The rate of a reaction was monitored by recording the volume of gas produced every 5 seconds.

What is the mean rate of reaction in the first 10 seconds of the reaction, in cm³ s^-1?

A student investigated the rate of reaction between dilute hydrochloric acid and marble chips (calcium carbonate).

Calcium chloride, carbon dioxide and water are formed.

Complete and balance the equation for the reaction.

   CaCO₃ + HCl → ....................... + ......................... + ......................

The student investigated the rate by using different sizes of marble chips. In their investigation, the same mass of marble chips was used in each experiment.

The volume of gas given off was measured.

The graph in Figure 8 shows the results.

Figure 8

(1)

(2)

rate of reaction =.............................................................cm³ s⁻¹

During any reaction, reactants are used up and the rate of reaction decreases.

Explain, in terms of particles, why the rate of reaction decreases.

The decomposition of hydrogen peroxide is catalysed by adding a small amount of manganese(IV) oxide.

Which of these graphs shows the mass of the catalyst as the reaction takes place?

	☐	A
	☐	B
	☐	C
	☐	D

Two gases, X and Y, react to give a gaseous product Z.

The reaction is carried out under two different sets of conditions in experiments 1 and 2 as shown in Figure 9.

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?

Hydrogen peroxide decomposes to form water and oxygen.

The rate of this reaction can be found by measuring the volume of oxygen formed after different time intervals.

Hydrogen peroxide solution is placed in a conical flask.
The apparatus is set up as shown in Figure 5.

Figure 5

At the end of the reaction the bung is removed from the conical flask.
A glowing splint is put into the gas in the flask.

State what you would see.

A solid catalyst can be used for this reaction.

The experiment is repeated three times

In each case, all other conditions are kept the same.

Circle the word that shows the change in the rate of decomposition in each case.

Complete the balanced equation for the reaction and fill in the two missing state symbols.

........................ H₂O₂ (aq) 2H₂O (........................) + O₂ (........................)

Magnesium metal reacts with an excess of hydrochloric acid solution to form magnesium chloride and hydrogen:

Mg (s) + 2HCl (aq) → MgCl₂ (aq) + H₂ (g)

Which of the following will not increase the rate of this reaction?

The word equation for the reaction between magnesium and dilute hydrochloric acid is

magnesium + hydrochloric acid → magnesium chloride + hydrogen

The reaction was carried out using the apparatus shown in Figure 11.

Figure 11

A strip of magnesium ribbon was placed in the conical flask.

100 cm³ of dilute hydrochloric acid was added to the conical flask.

The mass of the flask and contents was measured at regular intervals.

The loss in mass was calculated.

Figure 12 shows a graph of the results.

Figure 12

Explain why there is a loss in mass of the flask and contents.

The graph shows that the rate of reaction slows as the reaction takes place.

Explain, in terms of particles, why the rate of reaction between magnesium ribbon and dilute hydrochloric acid slows as the reaction takes place.

The experiment was repeated using the acid at a higher temperature.
All other conditions were kept the same.

State the effect of the higher temperature on the mass loss after two minutes.

The original experiment was repeated using the same mass of magnesium powder instead of the magnesium ribbon.

All other conditions were kept the same.

Sketch, on the graph in Figure 12, the line you would expect for this experiment.

Some reactions are affected by the presence of a catalyst.

(1)

(3)

Catalysts are often used in chemical reactions.

Which letter represents two correct features of catalysts?

Calcium carbonate reacts with dilute hydrochloric acid to produce calcium chloride,
water and carbon dioxide.

CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂

A student wanted to measure the amount of gas produced in two minutes.

The student suggested that this could be done by counting the number of bubbles formed.
However, the bubbles are produced too quickly to count them.

Figure 4 shows a conical flask in which the calcium carbonate and dilute hydrochloric acid are reacting.

Complete Figure 4 to show the apparatus that could be used to measure accurately the volume of gas given off in two minutes.

Figure 4

The reaction between calcium carbonate and dilute hydrochloric acid is exothermic.

Explain, in terms of bond breaking and bond making, why some reactions are exothermic.

An investigation was carried out into the rate of reaction of calcium carbonate with dilute hydrochloric acid.

5.0 g of small lumps of calcium carbonate were reacted with 50 cm³ of 0.50 mol dm^–3 hydrochloric acid.
Another 5.0 g of the same sized lumps of calcium carbonate were reacted with 50 cm³ of 1.0 mol dm^–3 hydrochloric acid.
The volume of gas collected in two minutes was recorded for each experiment.

The two experiments were then repeated, each using 5.0g of large lumps of calcium carbonate.

Figure 5 shows the results.

Figure 5

Explain, in terms of collision of particles, how these results show the effect of the size of the lumps of calcium carbonate and the effect of the concentration of the acid on the rate of this reaction.

Calcium carbonate reacts with hydrochloric acid to produce calcium chloride, water and carbon dioxide:

CaCO₃ (s) + 2HCl (aq) → CaCl₂ (aq) + H₂O (l) + CO₂ (g)

Which statement is not true if the temperature of the reaction decreases?

Calcium carbonate reacts with dilute hydrochloric acid to produce carbon dioxide gas.

The rate of reaction between calcium carbonate and dilute hydrochloric acid at room temperature was investigated.

Figure 15

State, using the information in Figure 15, the effect of the surface area of the calcium carbonate on the rate of this reaction.

(1)

average rate of reaction = ......................................... cm³ s^-1

Zinc metal reacts with dilute hydrochloric acid to produce hydrogen gas.

A student investigated the effect of doubling the concentration of the hydrochloric acid on this reaction.
The student made the following prediction.

Devise a plan, including the apparatus you would use, to test the student’s prediction.

You are provided with pieces of zinc and two bottles of dilute hydrochloric acid.
One bottle of hydrochloric acid is double the concentration of the other.

Magnesium reacts with hydrochloric acid to produce magnesium chloride and hydrogen gas:

Mg (s) + 2HCl (aq) MgCl₂ (aq) + H₂ (g)

During the first 10 s of the reaction, 1.2 g of magnesium was used up.

Calculate the mean rate of reaction, in mol s^-1, for this part of the reaction.

Relative atomic masses (A_r): H = 1, Mg = 24 and Cl = 35.5.

Magnesium reacts with dilute sulfuric acid to form magnesium sulfate and hydrogen gas.

A student wants to find out the effect of temperature on the rate of this reaction.

The student used the following method.

The student kept the volume of sulfuric acid the same when they repeated the method at 50 °C.

State two other variables that should be kept the same.

Which piece of equipment that can be used to find the volume of 25 cm³ of sulfuric acid?

State how the student will know that the reaction has finished.

The reaction at 50 °C was faster than the reaction at 30 °C.

Give one reason, in terms of particles, why the reaction at 50 °C was faster than the reaction at 30 °C.

At 50 °C, 15.0 cm³ of gas was produced during the first 60 seconds of the reaction.

Calculate the average rate of reaction, in cm³ s^–1, for the first 60 seconds of the reaction.

A student wants to investigate the effect of surface area on the rate of reaction between marble chips and dilute acid.

What pieces of apparatus could be used for this investigation?

Figure 9 shows a sample of hydrogen peroxide solution decomposing to form water and oxygen gas.

Figure 9

(1)

Describe the test to show the gas produced is oxygen.

Figure 10 shows the electron arrangement for an atom of hydrogen and an atom of oxygen.

Figure 10

Complete the dot and cross diagram in Figure 11 for a molecule of water, H₂O.

Draw outer shell electrons only.

Figure 11

Liver contains the enzyme catalase.

A piece of liver was added to another sample of hydrogen peroxide solution.

Figure 12 shows the results.

Figure 12

Figure 13 shows a graph of the volume of oxygen produced from the hydrogen peroxide with and without liver.

Figure 13

(1)

(2)

(2)

This question is about the rate of reaction between calcium carbonate and dilute hydrochloric acid.

The word equation for this reaction is

        calcium carbonate + hydrochloric acid → calcium chloride + water + carbon dioxide

Which of the following is the formula for calcium carbonate?

Some pieces of calcium carbonate were added to dilute hydrochloric acid in a conical flask and the volume of carbon dioxide produced was measured.

Complete the diagram in Figure 7 to show the apparatus to collect the gas produced and measure its volume.

The reaction between calcium carbonate and dilute hydrochloric acid was investigated at different temperatures.

Figure 8

Draw a tangent at 100 seconds on Figure 8.
Use this tangent to calculate the rate of reaction at this time.

(2)

rate of reaction = ................................ cm³ s^-1