The Rate and Extent of Chemical Change

Question 1

What is an example of a slow reaction?

Answer 1

The rusting of iron

Question 2

What is an example of a moderate speed reaction?

Answer 2

Magnesium reacting with acid to create a gentle stream of bubbles

Question 3

What is an example of a fast reaction?

Answer 3

Burning or an explosion

Question 4

How do you find the rate of a reaction?

Answer 4

By recording the amount of product formed or the amount of reactant used

Question 5

How is the rate of a reaction represented on a graph?

Answer 5

Steep line = faster rate
Less steep line = slower rate

Question 6

What does collision theory state?

Answer 6

A higher collision frequency of particles results in a faster reaction.

Question 7

What is activation energy?

Answer 7

The minimum amount of energy that particles need for a successful collision

Question 8

What are the four factors that can affect the rate of reaction?

Answer 8

Temperature, surface area, pressure/concentration, catalysts

Question 9

How does temperature affect the rate of reaction?

Answer 9

Increased temperature gives the particles more energy so they move faster which increases the number of successful collisions

Question 10

How do pressure and concentration affect the rate of a reaction?

Answer 10

More particles being present within a certain volume increases the likelihood of frequent successful collisions

Question 11

How does surface area affect the rate of reaction?

Answer 11

Breaking a solid reactant into more, smaller pieces increases its surface area to volume ratio which gives the particles around it more area to work on

Question 12

How does using a catalyst affect the rate of a reaction?

Answer 12

It speeds up the reaction without being used. It decreases the activation energy by providing an alternative reaction pathway

Question 13

How can you visually measure the rate of a reaction?

Answer 13

• turns from transparent to cloudy
• out a mark under the solution and see how long it takes to disappear
• see how long it takes for the solution to lose of gain colour

Question 14

How can you measure the rate of a reaction based on the change in mass (gas given off)?

Answer 14

Use a mass balance. As the gas is released, loss of mass is shown on the balance. The quicker the reading drops, the faster the reaction. Take regular readings to plot a graph. Very accurate.

Question 15

How do you measure the rate of a reaction based on the volume of gas given off?

Answer 15

Use a gas syringe. The more gas given off in a certain time period, the faster the reaction. Take regular readings to plot a graph. A vigorous reaction can blow the plunger out of the syringe.

Question 16

What do Magnesium and HCl react to produce?

Answer 16

Hydrogen (H2)

Question 17

How do you react Magnesium with HCl?

Answer 17

• add HCl to a conical flask on a mass balance
• add magnesium ribbon and plug with cotton wool
• time it and take readings at regular intervals
• record and plot the results
• repeat with different concentrations of acid solutions

Question 18

What is the result of reacting Sodium Thiosulfate and HCl?

Answer 18

They are both clear solutions and they react together to form a yellow precipitate of sulfur

Question 19

How do you react Sodium Thiosulfate and HCl

Answer 19

• add dilute sodium thiosulfate to a conical flask on top of a cross drawn on paper
• add some dilute HCl
• time how long it takes for the solution to cloud until you can’t see the cross anymore
• repeat with different concentrations

Question 20

What is the formula to calculate the mean rate of a reaction from a graph using two points?

Answer 20

Change in y / Change in x

Question 21

How do you find the rate of a reaction at a particular point on a graph?

Answer 21

Draw a tangent at the point and calculate it’s gradient

Question 22

What happens to the concentrations of reactions and products during a reversible reaction?

Answer 22

The concentration of the reactant falls, slowing the forward reaction down. The concentration of the product rises, speeding up the backwards reaction.

Question 23

What is equilibrium?

Answer 23

When the forward and backward reactions are going at exactly the same rate and have reached a balance. This means that even though the reactions keep happening, there is no overall change.

Question 24

What is the most important condition for equilibrium in a reversible reaction.

Answer 24

That it takes place in a closed system, where none of the reactant of products can escape.

Question 25

What does it mean if an equilibrium lies to the right?

Answer 25

The concentration of the products is greater than the concentration of the reactants.

Question 26

What does it mean if an equilibrium lies to the left?

Answer 26

The concentration of the reactants is greater than the concentration of the products.

Question 27

How does the concept of endo. and exothermic reactions relate to reversible reactions.

Answer 27

If a reaction’s endothermic in one direction the it will always be exothermic in the other and vice versa. The energy taken in is always equal to the energy put out.

Question 28

What does Le Chatelier’s Principle state?

Answer 28

That if you change the conditions of a reversible reaction at equilibrium, the system will try to counteract the change.

Question 29

How would Le Chatelier’s Principle apply to a change in temperature?

Answer 29

• Decrease in temperature = equilibrium moving to the exothermic direction = more products for the exothermic reaction.
• Increase in temperature = equilibrium moving to the endothermic reaction = more products for the endothermic reaction.

Question 30

How would Le Chatelier’s Principle apply to a change in pressure?

Answer 30

• only affects an equilibrium involving gases
• increase in pressure = equilibrium moving to the direction with fewer molecules of gas
• decrease in pressure = equilibrium moving to the direction with more molecules of gas

Question 31

How would Le Chatelier’s Principle apply to a change in concentration?

Answer 31

changing the concentration will mean the reaction is no longer at equilibrium so the system will try and restore the original concentration to bring itself back to equilibrium again.