Rate of Reaction (Cambridge (CIE) AS Chemistry)

A platinum-rhodium catalyst used in the reaction forming nitrogen(II) oxide from ammonia.

4NH₃ (g) + 5O₂ (g) ⇌ 4NO (g) + 6H₂O (g)

i) State what is meant by the term heterogeneous catalyst.

[1]

ii) Explain why a catalyst has no effect on the yield of the products in the reaction.

[1]

A group of students were completing a practical, investigating the factors which affect the rate of the following chemical reaction. 

A (s) + B (aq) → C (g)

The students collected the gas produced and plotted the graph shown in Fig. 1.1. 

Fig. 1.1

i) State and explain what the letter R represents on the student's graph.

[1]

ii) In the original reaction above, the students used 0.5 g of A and 50 cm³ of 1.0 mol dm^-3 of B. Sketch a curve on the graph in Fig 1.1 to show how the total volume of gas collected would change if the students still used 0.5 g of A, but used 50 cm³ of 2.0 mol dm^-3 of B.

[2]

Explain why the gradient of the curve in part (b) decreases as the time of the reaction progresses.

Another way to increase the rate of reaction is to increase the temperature. 

Explain why a small increase in temperature has a large effect on the initial rate of a chemical reaction.

This question is about how different factors affect the rate of a chemical reaction.

A reaction between reactant molecules can only occur when collisions between the reactant molecules are effective.

i) Explain what is meant by the term effective collision.

[1]

ii) State two factors that could cause an ineffective collision.

[2]

A student made the following statement about factors that affect the rate of a chemical reaction.

'The rate of a reaction increases with temperature as there are more collisions'

Discuss why this statement is only true to an extent and what other factors need to be considered to fully explain how the rate of a reaction is affected by temperature.

Hydrogen and oxygen can react to form water in an exothermic reaction.

2H₂ (g) + O₂ (g) → 2H₂O (g)

The rate of this reaction depends on the pressure as well as the temperature.

Describe and explain the effect of increasing the pressure on this reaction.

If the rate of reaction increases suddenly, an explosion can occur.

A highly exothermic reaction, such as the reaction in (c), is at more risk of exploding than a less exothermic reaction.

Suggest why.

A series of experiments was carried out to investigate the factors which affect the rate of reaction between calcium carbonate and dilute hydrochloric acid.

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

• 50.0 cm³ of hydrochloric acid was added to 10 g of small pieces of calcium carbonate (an excess) in a conical flask placed on an electronic balance.

• The loss in mass of the flask and its contents was recorded every 30 seconds for 10 minutes.

• The experiment was repeated using a different concentration of hydrochloric acid or a different temperature.

• The results are shown in Table 3.1

Table 3.1

The results of Experiment 1 are shown in Fig. 3.1.

Fig. 3.1

Draw curves on the graph in Fig 3.1 to show the results you would expect for Experiments 2 and 3.

Label the curves 2 and 3.

Determine the initial rate of reaction for Experiment 1.

You must show your working on the graph in Fig 3.2. Include units in your answer.

Fig 3.2

 Initial rate of reaction .........................................................

Calculate the average rate of reaction over the first 240 seconds of Experiment 1.

Average rate of reaction....................................................................

The student repeated each experiment but used 10.0 g of larger sized pieces of calcium carbonate.

Suggest what effect this would have on the rate of reaction. Give your reasoning.

0.5 g of magnesium reacts with 50 cm³ of 0.01 moldm^-3 nitric acid. Magnesium is in excess.

A graph monitoring the volume of hydrogen gas produced is shown below:

i) Calculate the mean rate of reaction over the first 15 seconds of the reaction

[1]

ii) Calculate the actual rate of reaction at 15 seconds

[3]

iii) Explain the difference in values for rate

[1]

Compare the expected rate and progress of the reaction if 25 cm³ of 0.2 mol dm^-3 nitric acid was used instead of 50 cm³ of 0.1 mol dm^-3 nitric acid.

Suggest one change to the reaction that could be made to produce more hydrogen gas in total and explain your choice.

Suggest why it is often better to study a slower reaction instead of a faster one.