topic 6

Question 1

What does the rate of a chemical reaction depend on (2)

Answer 1

• the collision frequency of reacting particles. The more collisions there are the faster the reaction is
• the energy transferred during a collision. Particles have to collide with enough energy for the collision to be successful

Question 2

The more collisions there are ….

Answer 2

The faster the reaction is

Question 3

What is the activation energy

Answer 3

The minimum amount of energy that particles need to react

Question 4

Why do particles need activation energy

Answer 4

To break the bonds in the reactants and start the reaction

Question 5

What is the rate of a reaction

Answer 5

How fast the reactants are changed into products

Question 6

2 examples of slow reactions

Answer 6

• rustling of iron

- chemical weathering- acid rain damaging limestone buildings

Question 7

An example of moderate speed reaction

Answer 7

-metal magnesium reacting with an acid to produce a gentle stream of bubbles

Question 8

How can you find the speed of a reaction

Answer 8

By recording the amount of product formed r the amount of reactant used up over time

Question 9

What does the rate of reaction depend on (4)

Answer 9

• temperature
• concentration of a solution or the pressure of gas
• surface area
• presence of a catalyst

Question 10

What does more collisions increase

Answer 10

It increases the rate of reaction

Question 11

3 ways in how increasing the temperature increases the rate

Answer 11

• when the temperature is increases, the particles all move faster
• if they are moving faster, they are going to collide more frequently
• the faster they move the more energy they have, so more of the collisions have enough energy to make the reaction happen

Question 12

What does it mean if a solution is more concentrated

Answer 12

It means there are more particles knocking about in the same volume of water or other solvent

Question 13

What happens when the pressure of gas is increased

Answer 13

It means the same number of particles occupies a smaller space- this makes collisions between the reactant particles more frequent

Question 14

How can you increase the surface area of a volume

Answer 14

If one of the reactants is a solid, then breaking it up into smaller pieces will increase its surface area to volume ratio

Question 15

How does increasing surface area increase rate

Answer 15

It means that for the same volume of the solid, the particles around it will have more area to work on so there will be collisions more frequently

Question 16

What is a catalyst

Answer 16

A substance that speed up the rate of a reaction without being used up in a reaction itself

Question 17

What do catalysts do in a rate of reaction

Answer 17

They 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

Question 18

What are enzymes

Answer 18

Biological catalysts- hey catalyse reactions in living things

Question 19

What is “Le Chatelier’s Principle”

Answer 19

The idea that if you change the conditions of a reversible reaction at equilibrium, the system will try to counteract that change

Question 20

What can “Le Chatelier’s Principle” be used to predict

Answer 20

The effect of any changes you make to a reaction system

Question 21

What does it mean if the equilibrium lies to the right

Answer 21

The concentration of products is greater than that of the reactants

Question 22

What does it mean if the equilibrium lies to the left

Answer 22

The concentration of reactants is greater than that of the products

Question 23

What does the position of equilibrium depend on what conditions (3)

Answer 23

• the temperature
• pressure
• concentration of the reactants and products

Question 24

if you decrease the temp of a system, what happens to the equilibrium

Answer 24

it moves in the exothermic direction to produce more heat- this means you get more products for the exothermic reaction and fewer products for the endothermic reaction

Question 25

what does changing the pressure have an affect on equilibrium involving …

Answer 25

gases only

Question 26

what happens to the equilibrium if you increase the pressure

Answer 26

the equilibrium tries to reduce it- it moves in the direction where there are fewer molecules of gas

Question 27

what happens to the equilibrium if you decrease the pressure

Answer 27

the equilibrium tries to increase it- it moves in the direction of where there are more molecules of gas

Question 28

when will a system no longer be at equilibrium

Answer 28

if you change the concentration of either the reactants or the products

Question 29

what happens to the system if you increase the concentration of the reactants

Answer 29

the system tries to decrease it by making more products

Question 30

what happens to the system if you decrease the concentration of products

Answer 30

the system tries to increase it again by reducing the amount of reactants

Question 31

what does it mean if a system is at equilibrium

Answer 31

both reactions are still happening, but there is no overall effect. This means that the concentration of reactants and products have reached a balance and won’t change

Question 32

how is equilibrium reached

Answer 32

equilibrium is only reached if the reversible reaction takes place in a ‘closed system’.

Question 33

what is a closed system

Answer 33

it means that none of the reactants or products can escape and nothing else can go in