SC18 Rates of Reaction

Question 1

Define rate of reaction

Answer 1

The speed at which reactants are turned into products

Question 2

How can we control the rate of a reaction?

Answer 2

By controlling the variables

Question 3

What are three commonly used techniques to measure the rate of a reaction?

Answer 3

1. measuring mass lost on a balance
2. measuring the volume of a gas produced
3. measuring a reaction where there is a colour change at the end of the reaction

Question 4

How can we use the change in mass to find the rate of the reaction?

Answer 4

• when gas is produced in a reaction, it usually escapes the reaction vessel, causing a loss in mass
• the difference between the initial mass and the final mass can be used to find out the rate of the reaction
• in a set period of time

Question 5

When are reaction rates usually the fastest and why?

Answer 5

At the start, because that is when the concentrations of all the reactants are the greatest

Question 6

When is measuring the change in mass not suitable?

Answer 6

When the gases produced have a small relative formula mass

Question 7

How can the rate be calculated?

Answer 7

(reactant used or product formed)/time taken

Question 8

When do we measure the change in the volume of a reactant or a product?

Answer 8

When a gas leaves the container

Question 9

How do we measure the volume of the gas leaving the reaction container?

Answer 9

Using:
- a gas syringe
- upside down burette
- measuring cylinder

Question 10

What is the collision theory?

Answer 10

When reactants come together, the kinetic energy they possess means that their particles will collide and some of these collisions will result in chemical bonds being broken and new bonds being formed

Question 11

What must occur for a chemical reaction to take place?

Answer 11

• particles must collide with each other
• particles must have enough energy for them to react

Question 12

Define activation energy

Answer 12

The minimum amount of energy needed for a collision to be successful

Question 13

What is the effect of increasing the concentration or pressure of a reacting component?

Answer 13

• the reactant particles are closer together
• the frequency of collisions between the reactant particles increases
• therefore increasing the rate of reaction

Question 14

What factors affect the rate of reaction?

Answer 14

• concentration and reaction rate
• surface area
• pressure of gases
• temperature

Question 15

How does the concentration of solutions increase the rate of reaction?

Answer 15

There are more reacting particles in the same volume so collisions occur more often

Question 16

How does an increase in surface area increase the rate of reaction?

Answer 16

More surface area of the particles will be exposed to the other reactant, producing a higher number of collisions per second

Question 17

How does an increase in the pressure increase the rate of reaction?

Answer 17

Reactant particles are squeezed closer together so collisions occur more often

Question 18

How does an increase in temperature result in an increase in the rate of reaction?

Answer 18

Particles will have more kinetic energy than the required activation energy , therefore there will be more frequent and successful collisions per second

Question 19

What variable is usually plotted on the x axis of a rate graph?

Answer 19

Time

Question 20

What are catalysts?

Answer 20

A substance that increases the rate of a reaction without altering the products of the reaction. It is chemically unchanged by the end of the reaction

Question 21

What do catalysts do?

Answer 21

Provide an alternative route for the reaction to take place

Question 22

What is the effect of a catalyst on the activation energy?

Answer 22

Lowers the activation energy, which provides a pathway requiring less energy

Question 23

Define enzymes

Answer 23

Biological enzymes

Question 24

Name an example of a enzyme

Answer 24

Yeast enzymes

Question 25

What do enzymes do?

Answer 25

• controlling reactions in cells
• to lower the temperature and the pressures of industrial reactions