Reaction Rates (kinetics)

Question 1

Reaction rate

Answer 1

Number of moles of product formed per second
OR
Numberof moles of reactant used per second

Question 2

What are the methods of measuring the rate of a reaction?

Answer 2

• Mass change
• Volume of gas
• Solid disappearing
• Color change

Question 3

How doe you measure the rate of a reaction using mass change?

Answer 3

Question 4

How do you measure the rate of a reaction using volume of gas?

Answer 4

By using two different methods. Either the dispalcement of water, or a gas syringe.

Question 5

How do you measure the rate of a reaction using solid disappearing?

Answer 5

1. Measure time until solid disappears
2. Do this several times
3. Calulate average

Question 6

How doe you measure the rate of a reaction using color change

Answer 6

1. Time until color change is observed
2. Calculate the rate

Question 7

What is the problem of measuring the rate of reactions uing solid disappearing?

Answer 7

• There is no graph and so, you can only calculate the average rate.

Question 8

What is the problem of using color change to measure the rate of reactions?

Answer 8

• There is no graph
• It is subjective

Question 9

How do you calculate the rate of a reaction at a specific point?

Answer 9

By using the graph and finding the tangent and calculating the gradient of that tangent.

Question 10

What is the trends with the rate of the reaction?

Answer 10

The rate of a reaction ALWAYS decreases from the beginging to the end. The initial rate is always the highest.

Question 11

Why does the rate of a reaction decrease as time passes?

Answer 11

Because the frequency of collisions decreases (collisions of particles colliding with eachother with eachother per second).

Question 12

Why does the frequency of the collisions between particles in a reaction decrease as the time increases?

Answer 12

This is because the reactants are used up during the reaction causing fewer to be availabe to react. At the end of the reaction there are no more reactants available. Therefore, no collisions can occur.

Question 13

What needs to occure for a reaction to happen?

Answer 13

During a reaction, particles need to collide. These collisions require 2 properties in order to be successful.

Question 14

What properties do the collision of particles require in order to be successful?

Answer 14

• Sufficient energy (activation energy)
• Correct orientation

Question 15

What factors can affect the rate of a reaction?

Answer 15

• Surface area
• Temperature
• Catalyst
• Concentration/preassure

Question 16

When do you use mass change to measure the rate of a reaction?

Answer 16

When a reaction produces gas or makes gas

Question 17

When do you use the volume of gas to measure the rate of a reaction?

Answer 17

when a reaction produces gas and there was no gas initially.

Question 18

When do you use solid disappearing to measure the rate of a reaction?

Answer 18

When an (aq) is produced from a solid and liquid.

Question 19

When do you use color change to measure the rate of a reaction?

Answer 19

When 2 (aq) are forming new chemicals and none of the other methods apply. (Displacement)

Question 20

When hydrogen is produced in a raction, should you use volume of gas produced or mass change to measure the rate of the reaction?

Answer 20

Usually, mass change would be used. However, hudrogen is very light and therefore, the mass change is hard to detect.

Question 21

What is the advantage of using vol. of gas to measure the rate of a reaction?

Answer 21

You can measure the rate of the reaction at any point of the reaction.

Question 22

What must occure for the rate of a reaction to increase?

Answer 22

• The frequency of collisions must increase
• The proportion of successful collisions must increase by:
  -changing the energy of particles
  -changing the orientation of particles

Question 23

Method to measure the effect of SA on the rate of a reaction.

Answer 23

• Measure 25cm³ of HCl into a chonical flask
• Record the mass of the apparatus
• Record the mass of CaCO₃ (calk form)
• Add CaCO₃ to HCl (on the balance)
• Start timing
• Record the mass every 20 seconds until reaction ceases
• Repeate with an equal mass of CaCO₃ powder

Question 24

Explain why there is a difference in reaction rate when using powdered solid instead of large pieces.

Answer 24

The pwdered solid has a higher SA, therefore, more particles are available to react at the SA of the solid. So, there is a higher frequency of collisionsbetween the paricles.

Question 25

What happens to the rate of a reaction when you increase the temperature?

Answer 25

Increasing the temp will increase the rate of a reaction through 2 factors:
* Particles gain energy, move faster and collide more frequently. (This affect is minor, there is only a slight change on the frequency)
* The proportion of particles with Ea is increased

Question 26

Use a graph to compare what occures in a reaction when the themp is increased.

Answer 26

Question 27

Why does the rate of a reaction increase with a higher temperature?

Answer 27

At a higher temp. a greater proportion of particles have the required Ea. It is more likely that each collision will be succesful. The frequency for successful collisions will increase and therefore, the rate shall as well. additionally, the particles will be moving faster as they have more energy. Therefeore, the collisions between reactants will be more frequent.

Question 28

What is the difference between energy and temperature?

Answer 28

Temp: the average energy/movement of particles (does not depend on no. of particles)
Energy: the total movement of particles in a subsatnce (depends on no. of particles)

Question 29

How does changing the concentration effect the rate of a reaction?

Answer 29

• Only affects solutions
• If there are more particles in the same volume then they will collide more frequently
• Increases the no. of reactant particles
• Increasing the concentration increases the number of reactant particles in a specific volume causes there to be more particles in the same volume. This results in an increased collision frequency.

Question 30

How does changing the surface area affect the rate of a reaction?

Answer 30

• Only affects solids
• Increases frequency of collisions
• Increases proportion of partic;es available to react

Question 31

How does changing the temperature affect the rate of a reaction?

Answer 31

• Increases collision frquency
• Increases proportion of successful collisions
• Increases proportion particles with Ea
• Affcts movement of particles

Question 32

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

Answer 32

• Increases collision frequency
• Increases proportion of successful collisions
• Affects the position of Ea
• Affects orientation of particles

Question 33

Catalyst

Answer 33

A substance which increases the rate of a reaction without being used up in the reaction.

Question 34

Why do catalysts affect the frequency of collisions with the right orientation?

Answer 34

Because one of the reactants ususally adsorbs to the catalyst due to the size of the catalyst particles. The frequency is increased since the reactant molecules are fixed in plave. Collisions are more likely to have the correct orentation due to the position of adsorbtion.

Question 35

Draw 2 graphs to show hoe catalysts affect the rate of a reaction

Answer 35

Question 36

Why would the rate in a reaction increase with time?

Answer 36

Because the reaction is exothermic. If the reaction releases sufficient energy and the temp. increases a lot, than the rate of the reaction will increase (freq. collsions + greater proportion of particles with sufficient energy)