Section 5 - Physical chemistry

Question 1

Define rate of reaction

Answer 1

How fast the reactants can are changed into products

Question 2

What is an example of a slow reaction?

Answer 2

Rusting

Question 3

What is an example of a moderate speed reaction?

Answer 3

Metal magnesium reacting with acid

Question 4

What is an example of a fast reaction?

Answer 4

An explosive reaction

Question 5

How can you work out the speed of a reaction?

Answer 5

Recording the amount of product formed or amount of reactant used up over time

Question 6

How can you measure the rate of reaction on a graph?

Answer 6

-The steeper the gradient the faster the rate of reaction
-The quickest reactions become flat in the least time

Question 7

What is the collision theory?

Answer 7

In order for a reaction to happen the particles must collide. The faster the reaction the more frequent successful collisions there are

And particles must have the minimum amount of energy (activation energy) in order for the collisions to be succesful

Question 8

What are the factors that increase the rate of reaction?

Answer 8

-Temperature
-Concentration of a solution or pressure of a gas
-Surface area
-Presence of a catalyst

Question 9

How does increasing the temperature increase the rate of reaction?

Answer 9

-When temperature is increased the particles move faster which means there will be more frequent successful collisions
-Higher temperatures also increase the energy of the collisions since the particles are moving faster

Question 10

How does increasing concentration increase rate of reaction?

Answer 10

-If a solution is made more concentrated it means there are more particles of the reactant in the same volume
-Therefore there are more particles which means there are more frequent successful collisions so rate increases

Question 11

How does increasing pressure increase rate of reaction?

Answer 11

-In a gas increasing the pressure means that the particles are more crowded
-This means there are more frequent successful collisions which increases the rate of reaction

Question 12

How does increasing the surface area increase rate of reaction?

Answer 12

-If you break a solid into loads of little pieces it increases its surface area to volume ratio
-Therefore more of the solid is exposed
-Therefore the particles will have more area to work on so there will be more frequent successful collisions
-This increases rate of reaction

Question 13

What is a catalyst?

Answer 13

A substance which increases the rate of reaction without being chemically changed or used up in a reaction

Question 14

How do catalysts work?

Answer 14

-They decrease the activation energy
-They do this by providing an alternate reaction pathway that has lower activation energy
-Therefore more particles have activation energy needed for a reaction to happen

Question 15

On a reaction profile how will the graph look different if there was a catalyst?

Answer 15

The highest point will be lower

Question 16

What is the equation for rate of reaction?

Answer 16

Amount of reactant used or amount of product formed/ time

Question 17

What is the precipitation method to measuring rate of reaction?

Answer 17

-This works when there are 2 see through solutions which produce a precipitate which clouds the solution

-Firstly you mix the 2 reactant solutions together and place the flask on a cross

-Then you observe the mark through the mixture and measure how long it takes for you to not be able to see the mark

-The faster it disappears the faster the reaction

Question 18

What is a disadvantage to the precipitate method to working out rate of reaction?

Answer 18

The result is subjective

Question 19

What is the change in mass method to measuring rate of reaction?

Answer 19

-You can measure the rate of a reaction that produces a gas using a mass balance

-As the gas is released the lost mass is easily measured on a balance

-The quicker the reading on the balance drops the faster the rate of reaction

-You can tell when the reaction is finished as there will be no more change to the mass balance

-Record the mass at certain time intervals and plot the results on a graph of change of mass against time

Question 20

What is a disadvantage to the change in mass method to working out rate of reaction?

Answer 20

The gas produced releases the gas straight into the room so if the gas is harmful then take safety precautions and do it in a fume cupboard

Question 21

What is the equipment needed in the precipitation method for measuring rate of reaction?

Answer 21

-Conical flask
-Paper with an x (mark) on it

Question 22

What is the equipment used in the change in mass experiment to work out rate of reaction?

Answer 22

-Mass balance
-Conical flask
-Cotton wool
-Stopwatch

Question 23

Why is cotton wool used when measuring rate of reaction using the change in mass method?

Answer 23

As the cotton wool lets gas escape however doesn’t let any solid, liquid or aqueous reactions fly out

Question 24

Describe the volume of gas given off experiment to measure the rate of reaction

Answer 24

-This involves the use of a gas syringe to measure the volume of gas given off

-The more gas given off during a set time interval the faster the reaction

-You can tell the reaction has finished when no more gas is produced

-You can use your results to plot a graph of gas volume against time elapsed

Question 25

What is a disadvantage to the volume of gas given off experiment to work out rate of reaction?

Answer 25

You need to use a right size gas syringe otherwise if the reaction is too vigorous then the plunger may blow out the other side

Question 26

What equipment is needed for the volume of gas given off experiment to work out rate of reaction?

Answer 26

-Conical flask
-Gas syringe

Question 27

Describe the experiment used to measure how surface area affects rate of reaction?

Answer 27

-Set up the required apparatus

-Measure the volume of gas produced from a conical flask with HCl and marble chips using a gas syringe taking regular readings at time intervals and record results

-Plot a graph of results (time on the x axis and volume on the y axis)

-Repeat the experiment with the same volume and same mass of marble chips but with them more crunched up

-Then repeat with powdered marble chips

Question 28

What is the apparatus required for the marble chip experiment to measure how surface area affects rates?

Answer 28

-Conical flask
-Marble chips
-HCl
-Gas syringe
-Stopwatch

Question 29

Describe the experiment that is used to work out how concentration affects the rate of reaction?

Answer 29

-Set up the required apparatus

-Measure the volume of gas produced from a conical flask with HCl and marble chips using a gas syringe taking regular readings at time intervals and record results

-Plot a graph of results (time on the x axis and volume on the y axis)

-Repeat the experiment with different concentrations of acid

-Then repeat with powdered marble chips

Question 30

Describe an experiment that is used to measure how temperature affects rate of reaction

Answer 30

-Sodium thiosulfate and HCl are both clear solutions and when reacted together form a yellow precipitate of sulfur

-You can measure rate of reaction by watching a black mark disappear through the cloud sulfur and timing how long it takes

-This is the repeated at different temperatures

-The best way to do it is in a water bath to heat the solutions to the right temperature before you mix them

NOTE: The depth of the liquid must be the same each time

Question 31

Describe an experiment on how you can measure how catalysts affect rate of reaction

Answer 31

-You use the decomposition of Hydrogen peroxide with the prescence of manganese (IV) oxide

-Copper(II) oxide and Zinc oxide also work as catalysts

-Set up the apparatus

-Add the desired catalyst

-Measure the volume of oxygen gas produced at certain time intervals

-Repeat with the same concentration of acid but different catalysts (the same mass)

Question 32

What is the apparatus used in the experiment used to measure how catalysts affect rate of reaction?

Answer 32

-Conical flask
-Gas syringe
-Hydrogen peroxide
-Catalyst

Question 33

What are the catalysts used in the experiment to work out how catalysts affect rate of reaction?

Answer 33

-With hydrogen peroxide the catalysts used are:

-Manganese (IV) oxide (MnO2)
-Copper (II) oxide (CuO)
-Zinc oxide (ZnO)

Question 34

What is the equation of the decomposition of hydrogen peroxide?

Answer 34

2H2O2(aq) -> 2H2(l) + O2(g)