Rate and extent of chemical change

Question 1

Explain the rate of chemical reactions

Answer 1

How fast the products are being formed / how fast the reactants are being used up

Question 2

Equation for rate of reaction

Answer 2

quantity of reactants used / time taken

Question 3

Factors that affect the rate of chemical reactions

Answer 3

• Catalyst
• Temperature
• Surface area
• Concentration / pressure

Question 4

What is the collision theory

Answer 4

For particles to react, they have to collide with each other with sufficient energy (AE)

Question 5

What affect the rate of reaction at a particular point

Answer 5

• The amount of energy the particles have. More energy they have = more energy they can transfer during collision = more likely to surpass activation energy
• The frequency of collisions. More often they collide = more successful collisions

Question 6

Why does rate of reaction increase as temperature increases

Answer 6

• Particles gain more energy
• So they move faster and collide more frequently
• Also, they collide with more energy and are therefore more likely to exceed activation energy

Question 7

Why does rate of reaction increase as conc/pressure increases

Answer 7

More particles per unit of volume
More frequent collisions

Question 8

Why does rate of reaction increase as surface area increases

Answer 8

Much higher area over which collisions with other reactants could take place
More frequent collision

Question 9

Why does rate of reaction increase as a catalyst is introduced

Answer 9

Catalyst lowers activation energy by providing alternate reaction pathway.
Higher proportion o successful collisions

Question 10

Describe a rate of reaction graph
(amount of reactant used on Y)
(time on X)

Answer 10

• Steeper at beginning as there is more reactant particles that can react together. Lots of products are produced, indicating high rate of reaction.
• As limiting reagent is used up, the products are produced more slowly, giving a less steep graph
• Eventually, the graph plateaus as the reactant has been fully used up

Question 11

When is a reaction at equilibrium

Answer 11

When the forward and backward reactions are happening at the same rate

Question 12

When there are fewer reactants than products, what would you say about equilibrium

Answer 12

Equilibrium lies to the right

Question 13

When there are more reactants than products, what would you say about equilibrium

Answer 13

Equilibrium lies to the left

Question 14

How does increased temperature change position of equilibrium

Answer 14

Favours the forward reaction (endothermic)
So we have more products
So equilibrium lies to the right

Question 15

In what conditions can a reversible reaction be reached

Answer 15

In a closed system
So none of reactants or products can escape

Question 16

What is Le Chatelier’s principle

Answer 16

The idea that id you change the conditions of a reversible reaction
The position of equilibrium will shift to try and counteract that change

Question 17

If pressure increases, where will equilibrium shift

Answer 17

Will shift to the side with less molecules to try to decrease the pressure again

Question 18

If concentration of a reactant increases, where will equilibrium shift

Answer 18

Will shift to the opposite side of the increased concentration