6. Chemical Reactions

Question 1

Equilibrium

Answer 1

The state achieved when the forward and reverse reactions occur at the same rate and the concentration of the reactants and products stay constant.

Question 2

Is White copper sulfate powder turning blue when water is added and white again when water is evaporated a chemical or physical reaction

Answer 2

Physical

Question 3

How can compounds be split up

Answer 3

chemical separating techniques such as electrolysis

Question 4

Difference between chemical and physical changes

Answer 4

In a physical reaction, the substance itself doesn’t change, only the form. E.g. changes of state
In a chemical reaction reactants are converted to products and have different properties
Physical changes are reversible, most chemical changes aren’t e.g. combustion

Question 5

What factors affect the rate of reaction (5)

Answer 5

Concentration
Pressure (only in gases)
Temperature
Catalyst
Surface area

Question 6

rate of reaction

Answer 6

The change in concentration per unit time of either the product or the reactants

Question 7

What is the formula for gases

Answer 7

v=n24

Question 8

How does concentration affect the rate of reaction

Answer 8

The higher the concentration the higher the number of particles per unit volume, resulting in more effective collisions per unit time and a faster reaction rate

Question 9

How does temperature affect the rate of reaction

Answer 9

As the temperature increases, the particles gain energy and move faster, resulting in more effective collisions per second with sufficient energy to react

Question 10

How does a catalyst affect the rate of reaction

Answer 10

By introducing a catalyst it lowers the activation energy resulting in a higher rate of effective collisions per second as more molecules collide with equal or greater activation energy.

Question 11

How does surface area affect the rate of a reaction

Answer 11

The smaller the particles size(the greater the surface area), the more surface exposed for reactions to take place, therefore there are more effective collisions per unit time.

Question 12

How does pressure affect the rate of reaction

Answer 12

Reducing the volume of the container means that you are reducing the space in which the gas particles can move, therefore more effective collisions per unit time.

Question 13

How can we measure the rate of a reaction

Answer 13

1. Measuring the volume of gas given off every minute
2. Measure the decrease in mass as the gas escapes

Question 14

How is nitrogen obtained

Answer 14

Distillation of liquid air

Question 15

How is hydrogen obtained

Answer 15

Methane

Question 16

What effect does equilibrium have on the concentration of the reactants/products in a reaction

Answer 16

None, they cancel each other out

Question 17

Homogeneous equilibrium

Answer 17

One in which all species present are in the same phase
E.g gas-phase/solution reactions

Question 18

Heterogeneous equilibrium

Answer 18

One in which the reactants, products, or both are in more than one phase
E.g reactions involving solids and gases or solids and liquids

Question 19

What are the characteristics/requirements of equilibrium

Answer 19

Constant concentration of reactants and products given there is no other change in the system
Dynamic-products and reactants changing into each other by chemical reactions constantly and at the same time
Must occur in a closed system so nothing can escape

Question 20

How does a catalyst effect equilibrium

Answer 20

It affects the rate of a reaction, but has no influence on the equilibrium of a reaction

Question 21

What factors affect equilibrium (3)

Answer 21

Temperature
Pressure (only in gasses)
Concentration

Question 22

What is the Haber process

Answer 22

The industrial process used to make ammonia

Question 23

What are the uses of ammonia

Answer 23

Nitric acid-cleaning products
Explosives
Fertilizers

Question 24

How is nitrogen gas obtained

Answer 24

From fractional distillation

Question 25

How is hydrogen gas obtained

Answer 25

Through cracking of natural gases

Question 26

Do you make or break bonds when making ammonia, therefore what is the forward reaction of ammonia

Answer 26

Make bonds Exothermic

Question 27

What is the equation for the haber process

Answer 27

N2(g) + 3H2(g) <->2NH3(g)

Question 28

What will a system do to try to increase pressure

Answer 28

It will shift in the direction of the most gas molecules

Question 29

What are the conditions of the harbour process and what do they do (3)

Answer 29

Iron catalyst-does not take part in the reaction, just facilitates it. It increases the rate of the reaction by lowering the activation energy Temperature-450*, it is low enough to favour the forward reaction, but high enough that the rate is economical-can’t be too low otherwise rate of reaction would be too slow Pressure-200atm/20 000kPa, high enough is needed to favour forward reaction, but not too high as maintaining pressure is very costly

Question 30

What are the uses of sulfuric acid (2)

Answer 30

Manufacture of paint Car batteries

Question 31

What is significant about the steps in the contact process

Answer 31

Only the second one is reversible

Question 32

How do they stop toxic gases released during the contact process from being released into the atmosphere

Answer 32

The chimneys are fired with acid scrubbers, bases Eg.(Na2CO3) Or by recycling gases between stage 2 and 3

Question 33

Major source of sulfuric

Answer 33

Crude oil/petroleum/fossil fuels

Question 34

Uses of sulfur dioxide (2)

Answer 34

Bleaching of wood fibres to make paper Food preservatives

Question 35

contact process conditions + reasons

Answer 35

450* Celsius - a lower temperature doesn’t produce an economical rate of SO3 and it would slow the reaction 200 kPa/2 atm pressure- high enough that equilibrium shifts in direction of lesser gas yield, low enough to be economical Vanadium (V) oxide catalyst V2O5 - to increase the rate of reaction

Question 36

Why can water not be directly reacted with sulfur trioxide

Answer 36

It is too volatile and a toxic gas is produced

Question 37

State 2 characteristics of an equilibrium

Answer 37

The rate of the forward reaction = rate of reverse reaction Concentration of reactants and products are constant

Question 38

Sources of hydrogen and nitrogen in the harbour process

Answer 38

Methane (cracking of natural gases) Fractional distillation of Air

Question 39

Haber process conditions (3)

Answer 39

450*C Iron catalyst 20 000 kPa/ 200 atm

Question 40

Sources of sulphur dioxide and oxygen in the contact process

Answer 40

Roasting sulphur ores Air

Question 41

Contact process equation

Answer 41

2SO2(g) + O2(g) ->REVERSIBLE<- 2SO3(g)

Question 42

How the addition of water to anhydrous compounds can change the direction of a reversible reaction

Answer 42

When anhydrous compounds are exposed to water, they can undergo a hydration reaction and become hydrated. This can shift the equilibrium of the reaction towards the products. However, if water is removed from the system, it can cause the hydrated compound to become anhydrous again, and shift the equilibrium towards the reactants. copper(II) sulfate - White- blue cobalt(II) chloride - blue - pink

Question 43

How the effect of heat on hydrated compounds can change the direction of a reversible reaction

Answer 43

When hydrated compounds are heated, the water molecules that are bound to the compound can be released, causing the compound to become anhydrous. This can shift the equilibrium of the reaction towards the products. On the other hand, if the hydrated compound is cooled, it can cause the water molecules to rebind with the compound, shifting the equilibrium towards the reactants. Copper (II) sulphate - blue - white Cobalt (II) chloride - pink - blue

Question 44

How to identify redox reactions when using acidified potassium manganate (VII)

Answer 44

KMnO4 is an oxidising agent which turns from purple to colourless when added to a reducing agent containing solution

Question 45

How to identify redox reactions when using Potassium iodide (KI)

Answer 45

KI is a reducing agent which when added to an acidified oxidising agent containing solution such as Cl(aq) or hydrogen peroxide (H2O2) turns the solution red-brown due to the formation of iodine