Rates of reaction

Question 1

What is collision theory?

Answer 1

The theory used to predict the rates of chemical reactions, particularly for gases.

Question 2

What has to occur for a chemical reaction to take place?

Answer 2

• Reactant particles must collide with each other

- The particles must have enough energy for them to react

Question 3

What happens when particles collide?

Answer 3

1. Two pairs of particles move towards each other
2. The pairs collide and reform so that each member of the original pair joins with a member of the other pair, forming two new pairs
3. The new pairs are now moving away from each other

Question 4

What are the two ways that mean rate of reaction can be calculated?

Answer 4

mean rate of reaction = quantity of reactant used/time taken

mean rate of reaction = quantity of product formed/time taken

Question 5

What increases with the number of successful collisions?

Answer 5

The rate of reaction.

Question 6

If the concentration of a reacting solution or the pressure of a reacting gas is increased:

Answer 6

• The reactant particles become more crowded
• The frequency of collisions between reactant particles increases
• The rate of reaction increases

Question 7

How do you calculate rate of reaction from a graph?

Answer 7

• You draw a tangent to find the change in mass or volume.

- then use the formula: rate of reaction = change in mass or volume of product/change in time

Question 8

If the surface area to volume ratio of a reacting solid is increased:

Answer 8

• More reactant particles are exposed at the surface
• The frequency of collisions between reactant particles increases
• The rate of reaction increases

Question 9

If the temperature of the reaction mixture is increased:

Answer 9

• Reactant particles move more quickly
• The energy of the particles increases
• The frequency of successful collisions between reactant particles increases
• The proportion of collisions which are successful increases
• The rate of reaction increases

Question 10

A catalyst is a substance that:

Answer 10

• Increases the rate of a reaction
• Does not alter the products of the reaction
• Is not chemically changed or used up at the end of the reaction

Question 11

What is the method for measuring the production of gas?

Answer 11

1. Support a gas syringe with a stand, boss and clamp.
2. Using a measuring cylinder, add 50 cm3 of dilute hydrochloric acid to a conical flask.
3. Add 0.4 g of calcium carbonate to the flask. Immediately connect the gas syringe and start a stop clock.
4. Every 10 seconds, record the volume of gas produced.
5. When the reaction is complete, clean the apparatus as directed by a teacher.
6. Repeat steps 1 to 5 with different concentrations of hydrochloric acid.

Question 12

Analysis of the practical: measuring the production of gas.

Answer 12

1. For each concentration of hydrochloric acid, plot a graph to show:
   - volume of gas (cm3) on the vertical axis
   - time (s) on the horizontal axis
   draw a curve of best fit
2. For each concentration of acid, calculate the mean rate of reaction until the reaction stops:
   mean rate of reaction = total mass of gas produced/reaction time

Question 13

What are the hazards, risks, and precautions for the practical: measuring production of gas.

Answer 13

Hazard: hydrochloric gas
Risk: causes skin and eye irritation
Precaution: wear eye protection

Hazard: fizzing in the reaction mixture
Risk: Acidic spray or foam escaping, which may damage skin and eyes
Precaution: Use a large conical flask so there is plenty of space inside, do not look over the top when adding the calcium carbonate

Question 14

What is the method for investigating the rate of reaction by colour change?

Answer 14

1. Using a measuring cylinder, add 50 cm3 of dilute sodium thiosulfate solution to a conical flask.
2. Place the conical flask on a piece of paper with a black cross drawn on it.
3. Using a different measuring cylinder, add 10 cm3 of dilute hydrochloric acid to the conical flask. Immediately swirl the flask to mix its contents, and start a stop clock.
4. Look down through the reaction mixture. When the cross can no longer be seen, record the time on the stop clock.
5. Measure and record the temperature of the reaction mixture, and clean the apparatus as directed by a teacher.
6. Repeat steps 1 to 5 with different starting temperatures of sodium thiosulfate solution.

Question 15

Analysis of the practical: investigating the rate of reaction by colour change.

Answer 15

1. Calculate 1000/time for each temperature. This value is proportional to the rate of reaction.
2. Plot a graph to show:
   - Reaction rate (/s) on the vertical axis
   - temperature (°C) on the horizontal axis
   - Draw a curve of best fit

Question 16

Hazards, risks and precautions of the practical: investigating the rate of reaction by colour change.

Answer 16

Hazard: Hot sodium thiosulfate solution.
Risk: Burns to the skin.
Precaution: Do not heat above 60°C.

Hazard: Sulfur dioxide.
Risk: Can cause irritation to the eyes and lungs, particularly to people with asthma.
Precaution: Make sure the room is well ventilated, avoid breathing directly over the top of the flask.