The Rate And Extent Of Chemical Change

Question 1

Rate of reaction=

Answer 1

Amount of reactant used or product formed/ time

Question 2

What are the different ways to find the rate of reaction?

Answer 2

• Measuring the time it takes for a reaction mixture to become opaque/change colour.
• Measuring the amount of products formed.
• Measuring amount of reactants used.

Question 3

How can you find the rate of reaction used by measuring the amount of reactants used?

Answer 3

• If one is a gas, measure the mass in grams of the reaction before and after.
• Mass of mixture will decrease.

As the reaction takes place, the reaction mixture is used up, so the amount of remaining reactant decreases. The concentration of the reactants is calculated as the amount is divided by the volume of the reaction mixture.

Question 4

What can the amount of reactant be measured in?

Answer 4

Moles

Question 5

How do you find the rate of reaction by measuring the amount of product formed?

Answer 5

If one of the products is a gas, measure the total volume of gas produced in centimetres cubed with a gas syringe and the time it takes for the reaction to happen rate of reaction is measured in centimetres cubed/s

Question 6

How do you find the rate of reaction by measuring the time it takes for a reaction mixture to become opaque/change colour?

Answer 6

Time how long it takes for the mixture to change colour.

Rate of reaction = 1/time taken for solution to change colour

Question 7

What are the important factors that affect the rate of reaction?

Answer 7

Temperature, SA, concentration, catalysts

Question 8

How does temperature affect the rate of reaction?

Answer 8

In a hot reaction mixture the particles move more quickly- they collide more often and with greater energy so more more collision are successful.

Question 9

How does concentration affect the rate of reaction?

Answer 9

At higher concentrations, the particles are crowded closer together so they collide more often. Increasing the pressure of reacting gases also increases the frequency of collisions.

Question 10

How does surface area affect the rate of reaction?

Answer 10

• Small pieces of a solid reactant have a larger surface area in relation to their volume.
• More particles are exposed and available for collisions, so there are more collisions and a faster reaction.

Question 11

What are key things to remember when plotting reaction rates?

Answer 11

• Steeper the line, faster the reaction
• When 1 reactant is used up, reaction stops (horizontal line)
• Same amount of product is formed from the same amount of reactants

Question 12

How do you work out the rate of a reaction at a particular time in a graph?

Answer 12

• Draw a tangent time the curve at that time
• Find gradient of tangent
• Gradient = rate of reaction at that time

Question 13

What are catalysts?

Answer 13

Substances that increase rate of chemical reaction without be used up.

Question 14

A catalyst:

Answer 14

• Reduces amount of energy needed for a successful collision.
• Makes more collisions successful
• Speeds up reaction
• Provides surface for molecules to attach to which increases chance of bumping into each other.

Question 15

Which different reactions use different catalysts?

Answer 15

• Cracking of hydrocarbons uses broken poverty.

- Manufacture of ammonia uses iron.

Question 16

What do catalysts help do in industry?

Answer 16

Reduce cost

Question 17

What happens in a reversible reaction?

Answer 17

In a reversible reaction the products can react to produce the original reactants.

Question 18

How can the direction of reversible reactions be changed?

Answer 18

By changing conditions

Question 19

If a reversible reaction is endothermic one way…

Answer 19

It is exothermic in the other.

Question 20

Energy given out in exothermic=

Answer 20

Energy taken in in endothermic

Question 21

What are closed systems?

Answer 21

Systems where no reactants are added and no products are removed.

Question 22

What happens when a reversible reaction occurs in a closed system?

Answer 22

An equilibrium is achieved Shen the rates of the forwards and backwards reactions are equal.

Question 23

What does Le Chatelier’s principle state?

Answer 23

That if a system in equilibrium is subjected to a change in conditions, the system then shifts to resist a change.

Question 24

In an exothermic reaction if the temperature increases the yield…

Answer 24

Decreases

Question 25

In an exothermic reaction if the temperature decreases the yield…

Answer 25

Increases

Question 26

In an endothermic reaction if the temperature increases the yield…

Answer 26

Increases

Question 27

In an endothermic reaction if the temperature decreases the yield…

Answer 27

Decreases

Question 28

In reactions involving gases what does an increase in pressure favour?

Answer 28

The reaction that produces the least number of gas molecules.

Question 29

In reactions involving gases what does an decrease in pressure favour?

Answer 29

The reaction that produces the most number of gas molecules.

Question 30

If the concentration of a reactant or product is change…

Answer 30

• the system is no longer in equilibrium

- the system adjusts to reach equilibrium

Question 31

If the concentration of one of the reactants increases what happens to the position of equilibrium?

Answer 31

It shifts so more products are formed until equilibrium is reached again.

Question 32

If the concentration of one of the reactants decreases what happens to the position of equilibrium?

Answer 32

It shifts so less products are formed until equilibrium is reached again.

Question 33

What is dynamic equilibrium?

Answer 33

In a reversible reaction where both products and reactions are in equilibrium and working at the same rate simultaneously.