The Rate And Extent Of Chemical Change

Question 1

Example of very fast reaction

Answer 1

Explosion of dynamite

Question 2

Example of very slow reaction

Answer 2

Rusting of steel

Question 3

What is the word for how fast a reaction is occuring

Answer 3

Rate of reaction

Question 4

Two formula for mean rate of reaction

Answer 4

Quantity of reactant used / time

Quantity of product formed / time

Question 5

What is quantity of reactant or quantity of product measured as

Answer 5

Grams (g)
Cubic centimetres (cm^3)
Moles (mol)

Question 6

What is time in rate of reaction measured in

Answer 6

Seconds

Question 7

Why is the rate of a reaction different if measured at different times and not the mean

Answer 7

Because the rate is constantly changing and most reaction are fastest at the beginning, slow down and then eventually stop, meaning the rate at one moment is likely to be different to the rate at another.

Question 8

What are on the axis’s for the rate of reaction graph

Answer 8

Time - y axis
Quantity of products formed - x axis

Question 9

How to measure volume of gas formed in a reaction

Answer 9

Set up apparatus - have a conical flask sealed with a rubber bung with the reaction mixture inside and a gas syringe going through the rubber bung into the conical flask. You should then record the volume of gas by the gas syringe readings every few seconds and plot it against time.

Question 10

How to measure mass of gas formed in a reaction and how to make it easier

Answer 10

Set up apparatus - place the conical flask which would be sealed with cotton wool and filled with the reaction mixture onto a balance. The gas escapes through the cotton wool and so the mass on the balance decreased due to this gas escaping. If the balance is set to zero with the apparatus and chemicals in the balance before the reaction starts then it is even easier to record the mass of gas produced every few seconds as the reaction takes place.

Question 11

How can the rate of reaction using graphs be compared

Answer 11

The steeper the slop of the line, the greater the rate of reaction and thus can be confirmed with the gradient of a tangent on the graph.

Question 12

How to find the rate of reaction at any time with a rate of reaction graph

Answer 12

1. Select the time at which you want to measure the rate
2. With a ruler, draw a tangent to the curve at that point (should have the same slope as the graph line at that point)
3. Choose two points a good distance apart on the tangent line and draw lines until they meet the axes
4. Find the slip using slope = change in y axis/change in x axis
5. The higher the slope/gradient the faster the rate of reaction

Question 13

What is activation energy

Answer 13

The minimum energy particles must have to react

Question 14

What must occur for a chemical reaction take place

Answer 14

The particles of the reactant must have the activation energy

Question 15

What are successful collisions

Answer 15

Collisions between reactant particles which collide with enough energy to react resulting in a reaction

Question 16

What are unsuccessful collisions

Answer 16

Collisions which do not result in a reaction as the reactant particles collide but do not have enough energy to react.

Question 17

Example of how a successful collision would occur

Answer 17

1. Reactant particles move towards each other
2. The reactant particles collide and react
3. Product particles move away from each other

Question 18

Factors affecting the rate of reaction

Answer 18

Temperature
Concentration of reactant in solution
Pressure of reactant gases
Surface area of solid reactants
The presence of catalysts

Question 19

How does temperature affect the rate of reaction

Answer 19

The higher the temperature, the faster a reaction. When the temperature is increased, the kinetic energy of the particles increases. This means that they will move faster and therefore collide more frequently. Since they all have more kinetic energy, this means more of the collisions will have enough energy to make the reaction happen.

Question 20

Example of moderate speed reaction

Answer 20

Metal magnesium reacting with acid to produce a gentle stream of bubbles

Question 21

An everyday example of the effect of temperature on chemical reactions

Answer 21

The use of fridges. When food goes off, chemical reactions take place. So the cold temperature of fridges slow down the rate of reactions that take place and slow down the rate at which food goes off.

Question 22

How does concentration of reactions in solution affect the rate of reaction

Answer 22

The higher the concentration, the greater the rate of reaction. This is because is the solution is more concentrated it means there are more particles knocking about in the same volume of solvent and because there are more reactant particles in the same volume, there will be more frequent collisions, resulting in an increase in rate of reaction

Question 23

How does increasing the pressure of reacting gases affect the rate of reaction

Answer 23

The higher the pressure of reacting gases, the greater the rate of reactants. This is because it meand that the same number of particles occupy a smaller space meaning the particles are closer together, resulting in more frequent collisions and therefore increase in rate of reaction.

Question 24

How does increasing the surface area of solid reactants affect rate of reaction

Answer 24

The greater the surface area of a solid reactant, the greater the rate of reaction. This is because when increasing the surface area, the particles around it will have more area to work on as, so there will be collisions more frequently and therefore increase rate of reaction.

Question 25

How to increase surface area of a solid reactant

Answer 25

Breaking a solid reactant into smaller pieces

Question 26

why does rate of reaction vary for one large piece of solid and the same solid but broken up into smaller pieces

Answer 26

The larger one will have a smaller surface area to volume ration and only reactant particles at the surface of the solid can collide with particles of this reactant. However in the broke up one, there are more pieces there are more reactant particles than can be collided with

Question 27

What is a catalyst

Answer 27

A substance that speeds up a chemical reaction but does not get used up

Question 28

How does a catalyst speed up the rate of reaction

Answer 28

It provides a different route (pathway) for the reaction that has a lower activation energy

Question 29

Three examples of catalysts

Answer 29

Iron in the production of ammonia from the reaction of hydrogen and nitrogen (the Haber process). Nickel in the production of margarine from reaction of vegetable oils with hydrogen Platinum in catalytic converters to remove some pollutants from the exhaust gases of cars

Question 30

What can be added to cars to reduce air pollution

Answer 30

Catalytic converters

Question 31

Is there more less or the same amount of catalyst at the end of the reaction than there was at the start and why

Answer 31

There is the same because the catalyst is not used up in a reaction

Question 32

Where can a catalyst be shown in an equation

Answer 32

On top of the arrow

Question 33

What are enzymes

Answer 33

Molecules that act as catalysts in biological systems

Question 34

Example of artificial use of enzymes

Answer 34

Biological washing powders contain protease enzymes to break down proteins in dirt on clothes

Question 35

Two Examples of enzymes

Answer 35

Amylase is an enzyme that catalyses the breakdown of starch into sugars Protease is an anzyme that catalyses the breakdown of protein into amino acids

Question 36

Proportionality of gas pressure, surface area of solid and concentration of solution all of reactants to rate of reaction

Answer 36

It is proportional

Question 37

Is temperature and rate of reaction proportional

Answer 37

No

Question 38

Define the term turbidity

Answer 38

The cloudiness of a solution

Question 39

What is a reversible reaction

Answer 39

A reaction where once the products have been made from the reactants, the products can react to reform the reactants.

Question 40

Why is temperature and rate of reaction not proportional

Answer 40

Because a small increase to temperature causes a big increase in rate of reaction. This is because a small increase in temperature lesss to many more particles having the activation energy.

Question 41

What is a reversible reaction

Answer 41

where once the products have been made from the reactants, the products can react to reform the reactants.

Question 42

1st example of reversible reaction

Answer 42

Anhydrous copper sulfate (white solid) + water (colourless liquid -> <- (arrows on top of each other) hydrated copper sulfate (blue solid) When the product is heated it breaks back down into the reactants

Question 43

2nd reversible reaction example

Answer 43

Ammonium chloride (white solid) -> <- (the arrows are on top of each other) ammonia (colourless gas) + hydrogen chloride (colourless gas) When cooled the products can go back into the reactant

Question 44

If a reversible reaction is exothermic in one direction then in the other reaction it is …

Answer 44

Endothermic and they will be the exact same energy release or use

Question 45

What is a closed system

Answer 45

Apparatus where no substances can get in or out

Question 46

What is dynamic equilibrium

Answer 46

Where both the forward and reverse reactions are taking place simultaneously and at the same rate.

Question 47

What occurs if a reversible reaction takes place in a closed system a

Answer 47

A dynamic equilibrium is reached

Question 48

When does the equilibrium position lie to the left

Answer 48

When there are more reactants than products in the mixture of chemicals at equilibrium

Question 49

When does the equilibrium lie somewhere in the middle

Answer 49

When there is a similar amount of reactants and products in the mixture of chemicals at equilibrium

Question 50

When does the equilibrium lie to the right

Answer 50

When there are more products than reactants in the mixture of chemicals at equilibrium

Question 51

What does Le Châtelier’s principle state

Answer 51

It a change is made to the conditions of a system at equilibrium, then the position of the equilibrium moves to oppose that change in conditions.

Question 52

What happens to equilibrium if concentration of a reactant increases

Answer 52

Equilibrium position moves right to reduce concentration of reactant

Question 53

What happens to equilibrium if concentration of a reactant decreases

Answer 53

Equilibrium position moves left to increase concentration of reactant

Question 54

What happens to equilibrium if concentration of a product decreases

Answer 54

Equilibrium position moves right to increase concentration of product

Question 55

What happens to equilibrium if concentration of a product increases

Answer 55

Equilibrium position moves left to reduce concentration of product

Question 56

How does equilibrium change when changing temperature

Answer 56

In order to increase the temperature the equilibrium position moves in the direction of exothermic reaction. In order to decrease the temperature, the equilibrium position moves in the direction of the endothermic reaction.

Question 57

What happens to equilibrium when there is an increase in temperature and the forward reaction is exothermic

Answer 57

Equilibrium moves left in endothermic direction to lower the temperature

Question 58

What happens to equilibrium when there is a decrease in temperature and the forward reaction is exothermic

Answer 58

The equilibrium position moves right in exothermic direction to increase the temperature

Question 59

What happens to equilibrium when there is a decrease in temperature and the forward reaction is endothermic

Answer 59

The equilibrium position moves left in exothermic direction to increase the temperature

Question 60

What happens to equilibrium when there is a increase in temperature and the forward reaction is endothermic

Answer 60

The equilibrium position moves right in endothermic direction to increase the temperature

Question 61

Why are reactions where more product is formed at lower temperatures not usually carried out at low temperature and what is done instead

Answer 61

Because they would be far too slow. Instead a compromise temperature is usually used that gives a reasonable yield if product at a fast rate

Question 62

The more molecules that are present in a gas…

Answer 62

The grater the pressure of the gas

Question 63

What happens to equilibrium when pressure of an equilibrium containing gases changes

Answer 63

The position of the equilibrium will move to oppose that change (if it can). In order to increase the pressure, the equilibrium position moves to the side with the most gas molecules. In order to decrease the pressure, the equilibrium moves to the side with fewer gas molecules

Question 64

Why is the use of high pressure very expensive

Answer 64

Due to the high energy cost of compressing gases and the cost of pipes to withstand that pressure

Question 65

Why might actual optimum pressure of gas not be as high as expected to maximise rate of reaction

Answer 65

Because it’s not cost effective. Because the use of high pressure is expensive. In reactions where higher pressure gives more product, the value of the extra product formed is sometimes less than the cost of those higher pressure. The pressure used is often a compromise between the amount of product formed and the cost of using higher pressure

Question 66

How do catalysts effect the position of the equilibrium

Answer 66

They do not at all, rather they increase the rate of forward and backward reactions, both by the same amount. This means that the system reachers equilibrium faster and the product is formed faster.