C6 Rates

Question 1

What is the rate of a chemical reaction in terms of reactants?

Answer 1

How quickly the reactants in a reaction are used up

Question 2

What is the rate of a chemical reaction in terms of products?

Answer 2

How quickly the products in a reaction are formed

Question 3

What is the formula for a mean rate of reaction in terms of reactants?

Answer 3

quantity of reactant used/time taken

Question 4

What is the formula for a mean rate of reaction in terms of products?

Answer 4

quantity of reactant product formed/time taken

Question 5

How can you measure the quantity of a reactant or product?

Answer 5

In grams or in cm³

Question 6

What are the possible units for rate of reaction?

Answer 6

g/s, cm³/s or mol/s (where s is seconds)

Question 7

How could you measure the rate of a reaction from a graph?

Answer 7

Draw a tangent to the curve and calculate the gradient.

Question 8

What is a tangent line?

Answer 8

A straight line that just touches the curve of best fit

Question 9

How do you calculate a gradient?

Answer 9

change in values on y axis ÷ change in values on x axis

Question 10

What is “collision theory”?

Answer 10

The theory that chemical reactions only occur when particles collide with enough energy

Question 11

What factors can affect the rate of a reaction?

Answer 11

Temperature, surface area of a solid, concentration or reactants in solution, pressure of gases

Question 12

State the effect of increasing the surface area on the rate of a reaction

Answer 12

Increases the rate

Question 13

How can you increase the surface area of a solid?

Answer 13

Break it into smaller pieces.

Question 14

Explain why increasing the surface area increases the rate of a reaction

Answer 14

More particles are available to collide, there are therefore more frequent collisions between reactants.

Question 15

State the effect of increasing the concentration on the rate of reaction

Answer 15

Increases

Question 16

Explain why increasing the concentration increases the rate of reaction

Answer 16

More particles in the same volume, therefore more frequent collisions between reactants.

Question 17

State the effect on increasing the pressure of a gas on the rate of reaction

Answer 17

Increases

Question 18

Explain why increasing the pressure of a gas increases the rate of a reaction

Answer 18

More particles in the same volume, therefore more frequent collisions between reactants.

Question 19

State the effect of increasing the temperature on the rate of reaction

Answer 19

Increases

Question 20

What is the activation energy?

Answer 20

The energy needed to break bonds to start a reaction

Question 21

Explain why increasing the temperature increases the rate of reaction

Answer 21

Increases the kinetic energy of the particles so more frequent collisions, it also increases the number of particles which have the activation energy therefore more collisions result in a reaction.

Question 22

What is a catalyst?

Answer 22

Something which changes the rate of a reaction but is not used up in that reaction

Question 23

How do catalysts speed up reactions?

Answer 23

They provide another route for the reaction with a lower activation energy.

Question 24

What is a reversible reaction?

Answer 24

A reaction which can go from reactants to products but also from products to reactants

Question 25

What chemical symbol represents a reversible reaction?

Answer 25

⇌

Question 26

If a reaction is exothermic in the forward direction what will it be in the reverse direction?

Answer 26

Endothermic

Question 27

Two reactants require 30kJ to turn into products. What energy transfer is involved when the products turn into reactants?

Answer 27

30kJ is released

Question 28

What is equilibrium?

Answer 28

When the forward and backwards reactions are occurring at the same rate in a closed system

Question 29

How is the amount of reactant changing at equilibrium?

Answer 29

It is not changing

Question 30

How is the amount of product changing at equilibrium?

Answer 30

It is not changing

Question 31

What is Le Chatelier’s principle?

Answer 31

When a reaction at equilibrium is changed, it will seek to counteract that change

Question 32

How does increasing the concentration of a chemical affect the equilibrium position?

Answer 32

The equilibrium will shift away from that chemical until it reaches equilibrium again

Question 33

How does increasing the temperature of they system affect the equilibrium position?

Answer 33

The equilibrium shifts to the side with the least gas molecules until it reaches equilibrium again

Question 34

How does increasing the pressure of they system affect the equilibrium position?

Answer 34

The equilibrium shifts to the endothermic side until it reaches equilibrium again

Question 35

A reaction is exothermic in the forward direction. What will occur if the temperature is increased?

Answer 35

The backward reaction will increase as it is endothermic.

Question 36

A reaction is at equilibrium when some product is removed. What will occur?

Answer 36

The forward reaction will increase as that will increase the amount of product

Question 37

The reaction below is at equilibrium. What will occur when the pressure is increased? 2H₂(g) + O₂(g) ⇌ 2H₂O(g)

Answer 37

The forward reaction will increase as there are fewer molecules on the right.