Rates of Reactions

Question 1

What is Collision Theory?

Answer 1

Chemical reactions can only take place when the reacting particles collide with each other. The collisions must have sufficient energy. The rate of reaction is determined by the frequency of successful reactions.

Question 2

What happens to the rate of reaction if concentration is increased?

Answer 2

There are more reactant particles moving together, so the frequency of collisions would increase. So rate of reaction increases (faster reaction).

Question 3

What happens if we increase the surface area?

Answer 3

More particles are exposed to the other reactant. Greater chance of particles colliding, leading a higher frequency of collisions. Rate of reaction increases.

Question 4

Investigating the effect of surface area on the rate of reaction:

Answer 4

1. Marble chips contain calcium carbonate.
2. Reacts with hydrochloric acid to produce carbon dioxide gas.
3. Measure the volume of carbon dioxide and use this to determine the rate of reaction.
4. Then change the surface area of the marble chips.
5. Measuring the volume of gas can be difficult using a measuring cylinder as the bubbles can be rapid.
6. A gas syringe is more accurate.
7. Or you can measure the mass of carbon dioxide lost.

Question 5

What is activation energy?

Answer 5

The minimum amount of energy needed for a reaction to take place/particles to collide successfully.

Question 6

Effect of increasing temperature on rate of reaction?

Answer 6

Increases the rate of reaction. The energy of the particles is increased so they move faster. This increases the frequency of collisions. Each collision has more energy so more particles overcome the activation energy barrier and collide successfully.

Question 7

How do catalysts increase the rate of reaction?

Answer 7

They provide alternate pathway for the reaction to take which has a lower activation energy. This means particles require less energy to overcome the activation energy barrier. So the frequency of successful collisions is increased.

Question 8

What is Le Chatelier’s Principle?

Answer 8

If a system is at equilibrium and a change is made to the conditions, then the system responds to counteract the change.

Question 9

Does exothermic or endothermic increase the temperature of the reaction?

Answer 9

Exothermic.

Question 10

What is meant by a hypothesis?

Answer 10

A proposal that could explain a fact or an observation. This must be testable.

Question 11

What happens if we increase the pressure on a reversible reaction at equilibrium?

Answer 11

The position of equilibrium shifts to the side with the smaller number of molecules.

Question 12

What happens if we decrease the pressure of a reversible reaction at equilibrium?

Answer 12

The position of equilibrium shifts to the side with the larger number of molecules.

Question 13

What if we change the pressure and there is the same number of molecules on each side?

Answer 13

Then changing the pressure would have no effect on the position of equilibrium.

Question 14

What is meant by equilibrium?

Answer 14

The rate of forward and backward reactions are equal in a closed system.

Question 15

Exploring the effect of concentration (RP5)

Disappearing cross

Answer 15

Use a measuring cylinder to put 10cm^3 of sodium thiosulfate solution into a conical flask.
Place the conical flask onto a printed black cross.
Add 10cm^3 of hydrochloric acid into the conical flask.
Swirl the solution and start a stopwatch.
Look down through the top of the flask.
After a certain time, the solution will turn cloudy.
Stop the clock when you can no longer see the cross.
Carry out the experiment again using lower concentrations of sodium thiosulfate solution.
Repeat the whole experiment and calculate the mean values for each concentration of sodium thiosulfate solution.
Do not include anomalous results.

Question 16

What makes the solution go cloudy? (disappearing cross)

Answer 16

sulfur

Question 17

What is meant by reproducibility.

Answer 17

A measurement is reproducible if it can be repeated by another person or using a different technique or equipment and still get the same result.

Question 18

What is the problem with the disappearing cross?

Answer 18

Different people have different eyesights.

So some people can see the cross longer than others so they may not get the same results.

Question 19

Exploring the effect of concentration (RP5)

Measuring the volume of hydrogen gas produced.

Answer 19

Use a measuring cylinder to place 50cm^3 of hydrochloric acid into a conical flask.
Attach the conical flask to a bung and delivery tube.
Place the delivery tube into a container filled with water.
Then place an upturned measuring cylinder also filled with water over the delivery tube.
Add a 3cm strip of magnesium to the hydrochloric acid and start a stopwatch.
The reaction produces hydrogen gas which is trapped in the measuring cylinder.
Every 10 seconds, red the volume of hydrogen gas in the measuring cylinder.
Continue until no more hydrogen is given off.
Repeat the experiment using different concentrations of hydrochloric acid.

Question 20

What do these experiments show us?

Answer 20

The greater the concentration of a chemical in a reaction, the faster the reaction takes place.
This finding is reproducible as this result was shown by two different experiments.