Topic 6- Rates Of Reaction

Question 1

What is the rate of a chemical reaction?

Answer 1

How fast the reactants are changed into products.

Question 2

Name two of the slowest rate of reaction

Answer 2

Rusting of iron.
Chemical weathering.

Question 3

Give an example of a moderate speed reaction

Answer 3

Magnesium reacting with an acid to produce a gentle stream of bubbles

Question 4

Give an example of a fast speed reaction

Answer 4

Explosive reactions as they happen in a fraction of a second

Question 5

Two facts about graphs for rates of reactions

Answer 5

• the steeper the line, the faster the reaction. Overtime the line becomes less steep at the reactants are being used up.
• the quickest reactions have the steepest lines and become flat in less time.

Question 6

How to calculate rates of reaction.

Answer 6

Mean rate of reaction = quantity of reactant used/ time
Or
Mean rate of reaction = quantity of products formed/ time

Question 7

What is the collision theory?

Answer 7

For a chemical reaction to occur the reacting particles need to collide with one another

Question 8

What does the rate of a chemical reaction depend on?

Answer 8

• the collision frequency of reacting particles (how often they collide). The more collisions the faster the reaction is. Doubling frequency of collisions doubles the rate.
• the energy transferred during a collision. Particles have to collide with enough energy for the collision to be successful.

Question 9

What is a successful collision?

Answer 9

A collision that ends in the particle reactions to from products

Question 10

What is a drawback to fast rates of reactions?

Answer 10

• costs: it may be expensive to generate the conditions for very fast reactions.
• there can be safety concerns with very fast reactions.

Question 11

What do the rates of reactions depend on?

Answer 11

• temperature
• the concentration of a solution or the pressure of a gas.
• surface area: this changes depending on the size of the solid.
• presence of a Catalyst.

Question 12

How does increasing the temperature increase the rate of reaction?

Answer 12

1) when the temperature is increased, the particles move faster.
2) if they’re moving faster, they’re going to collide more frequently.
3) also, the faster they move the more energy they have, so more of the collisions will have enough energy to make the reaction happen.

Question 13

How does increasing the concentration or pressure increase the rate?

Answer 13

1) if a solution is made more concentrated, it means there are more particles knocking about in the same volume of water ( or other solvent).
2) similarly, when the pressure of a gas is increased, it means that the same number of particles occupies the smaller space.
3) this makes the collisions between the reactant particles more frequent.

Question 14

How does increasing the surface area increase the rate of reaction?

Answer 14

1) if one of the reactants is a solid, then breaking it up into smaller pieces will increase its surface area to volume ratio.
2) this means that for the same volume of the solid, the particles around it will have more area to work on — so there are more collisions.

Question 15

How does using a catalyst increase the rate of reaction?

Answer 15

1) a catalyst is a substance that speeds up a reaction, without being used up in the reaction itself. This means it’s not part of the overall reaction equation.
2) different catalysts are needed for different reactions, but they all work by decreasing the activation energy needed for the reaction to occur. They do this by providing an alternative reaction pathway with a lower activation energy.
3) enzymes are biological catalysts. (they catalyse reactions in living things)

Question 16

What is the le chatelier principle?

Answer 16

If you change the conditions of a reversible reaction the system will try to counteract the change

Question 17

Required practical: measuring the production of a gas. What is the method?

Answer 17

1) clamó a gas syringe to a record stand using a boss and clamp. Ensure the syringe is a quarter of the way from the top of the stand. Place the delivery tube to the end of the gas syringe.
2) measure out 50ml of hydrochloric acid using a measuring cylinder and pour it in the conical flask.
3) using a top pan balance, measure out 0.5g of powdered calcium carbonate and place in the conical flask.
4) immediately connect the bung and delivery tube to the conical flask. Start the stop watch.
5) record the volume of carbon dioxide gas produced every 10 seconds.
6) when the reaction has finished and there are no more bubbles of gas being produced, clean the equipment and repeat using four different concentrations of hydrochloride acid.

Question 18

What is the chemical equation for measuring the production of a gas?

Answer 18

Calcium carbonate + hydrochloric acid —> calcium chloride + water + carbon dioxide

Question 19

What is the symbol equation for measuring the production of a gas.

Answer 19

CaCO3 + 2HCl —> CaCl2 + H2O +CO2

Question 20

Required practical: investigating a change in colour. What is the method?

Answer 20

1) place a black cross on a white tile.
2) using the first temperature, measure out 35cm^3 of sodium thiosulfate using a measuring cylinder. Place the liquid in a conical flask and position it over the black cross on the white tile.
3) measure out 5cm^3 of water and 10cm^3 of hydrochloric acid in separate measuring cylinders.
4) pour the water and acid into the conical flask.
5) pour the measured amount of sodium thiosulfate into the conical flask and immediately start the stopwatch.
6) look down through the conical flask to the black cross below. When the black cross is no longer visible, stop the stopwatch and record the results on a table.
7) repeat the steps with the remaining temperatures of sodium thiosulfate.