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IGCSE Chemistry > 6. Chemical Reactions > Flashcards

6. Chemical Reactions Flashcards

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1
Q

Equilibrium

A

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

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2
Q

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

A

Physical

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3
Q

How can compounds be split up

A

chemical separating techniques such as electrolysis

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4
Q

Difference between chemical and physical changes

A

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

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5
Q

What factors affect the rate of reaction (5)

A

Concentration
Pressure (only in gases)
Temperature
Catalyst
Surface area

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6
Q

rate of reaction

A

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

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7
Q

What is the formula for gases

A

v=n24

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8
Q

How does concentration affect the rate of reaction

A

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

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9
Q

How does temperature affect the rate of reaction

A

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

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10
Q

How does a catalyst affect the rate of reaction

A

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.

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11
Q

How does surface area affect the rate of a reaction

A

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.

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12
Q

How does pressure affect the rate of reaction

A

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.

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13
Q

How can we measure the rate of a reaction

A
  1. Measuring the volume of gas given off every minute
  2. Measure the decrease in mass as the gas escapes
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14
Q

How is nitrogen obtained

A

Distillation of liquid air

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15
Q

How is hydrogen obtained

A

Methane

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16
Q

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

A

None, they cancel each other out

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17
Q

Homogeneous equilibrium

A

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

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18
Q

Heterogeneous equilibrium

A

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

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19
Q

What are the characteristics/requirements of equilibrium

A

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

20
Q

How does a catalyst effect equilibrium

A

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

21
Q

What factors affect equilibrium (3)

A

Temperature
Pressure (only in gasses)
Concentration

22
Q

What is the Haber process

A

The industrial process used to make ammonia

23
Q

What are the uses of ammonia

A

Nitric acid-cleaning products
Explosives
Fertilizers

24
Q

How is nitrogen gas obtained

A

From fractional distillation

25
Q

How is hydrogen gas obtained

A

Through cracking of natural gases

26
Q

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

A

Make bonds
Exothermic

27
Q

What is the equation for the haber process

A

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

28
Q

What will a system do to try to increase pressure

A

It will shift in the direction of the most gas molecules

29
Q

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

A

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

30
Q

What are the uses of sulfuric acid (2)

A

Manufacture of paint
Car batteries

31
Q

What is significant about the steps in the contact process

A

Only the second one is reversible

32
Q

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

A

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

33
Q

Major source of sulfuric

A

Crude oil/petroleum/fossil fuels

34
Q

Uses of sulfur dioxide (2)

A

Bleaching of wood fibres to make paper
Food preservatives

35
Q

contact process conditions + reasons

A

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

36
Q

Why can water not be directly reacted with sulfur trioxide

A

It is too volatile and a toxic gas is produced

37
Q

State 2 characteristics of an equilibrium

A

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

38
Q

Sources of hydrogen and nitrogen in the harbour process

A

Methane (cracking of natural gases)
Fractional distillation of Air

39
Q

Haber process conditions (3)

A

450*C
Iron catalyst
20 000 kPa/ 200 atm

40
Q

Sources of sulphur dioxide and oxygen in the contact process

A

Roasting sulphur ores
Air

41
Q

Contact process equation

A

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

42
Q

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

A

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

43
Q

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

A

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

44
Q

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

A

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

45
Q

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

A

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

IGCSE Chemistry (21 decks)

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