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IGCSE Chemistry > Topic 6: Chemical reactions > Flashcards

Topic 6: Chemical reactions Flashcards

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1
Q
A
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2
Q

What are physical changes?

A

Changes that involve the states of matter and energy.
They are reversible; there are no new substances made, it is only the appearance of the substance that changes

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3
Q

Give examples of physical changes.

A

Changes in state
Dissolving
Mixing two solids (e.g. sand and soil)

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4
Q

What are chemical changes?

A

Changes that involve the bonds being broken and new ones being formed.
They are often irreversible

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5
Q

Give examples of indications of a chemical change.

A

Bubbles or releasing gas
Absorbing or releasing heat
Changing colour
Releasing an odour
Inability to reverse the change
Precipitation of a solid from a liquid solution
The formation of a new chemical

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6
Q

Give examples of chemical changes

A

Rusting
Neutralisation
Electrolysis
Digestion
Respiration
Souring of milk
Baking a cake

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7
Q

What is a reaction rate?

A

A measure of how long it takes for a reactant to be used up or a product to be formed.

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8
Q

What is the rate of reaction affected by?

A

Temperature
Concentration
Pressure of gases
Surface area of reacting solids
Use of catalysts

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9
Q

How does surface area affect reaction rate?

A

If reactant molecules exist in different phases, the rate of reaction will be limited by the surface area of the phases that are in contact.

Powders react faster than blocks - greater surface area and since the reaction occurs at the surface we get a faster rate

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10
Q

How does concentration affect reaction rate?

A

Increasing the concentration of one or more reactants will often increase the rate of reaction.

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11
Q

How does temperature affect reaction rate?

A

Rate of reactions speed up with increasing temperature

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12
Q

How does a catalyst affect reaction rate?

A

The presence of a catalyst increases the rate of reaction by providing an alternate pathway which has lower activation energy

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13
Q

How does pressure affect reactant rates?

A

Pressure increases the concentration of gases which in turn results in the increase of the rate of reaction.
The reaction rate increases in the direction of less gaseous molecules and decreases in the reverse direction.

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14
Q

What does the rate of reaction depend on?

A

The rate of successful collisions between reactant particles. The more successful collisions there are, the faster the rate of reaction.

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15
Q

Explain how surface area affects the rate of reaction (collision theory)

A

Increase in surface area of a solid reactant results in an increase in the number of collisions and this results in an increase in the number of successful collisions

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16
Q

Explain how concentration affects the rate of reaction (collision theory)

A

More particles in a more concentrated solution so collision rate between reactant particles is higher. The more often the particles collide, the greater the chance they have to overcome the activation energy and of a successful collision occurring.

17
Q

Explain how temperature affects the rate of reaction (collision theory)

A

As the temperature increases, the reactant particles increase their kinetic energy and they move faster, resulting in more collisions between the particles. Theis causes the reaction rate to increase.

18
Q

Explain how a catalyst affects the rate of reaction (collision theory)

A

Provides an alternative reaction path which has a lower activation energy. This causes more of the collisions to become successful, increasing the rate of reaction.

19
Q

Explain how pressure affects the rate of reaction (collision theory)

A

Increase in pressure results in the gas particles being push closer together, increasing the number of particles per unit volume. This means that they collide more frequently, and so the rate of reaction increases.

20
Q

What is a catalyst?

A

A substance which can alter the rate of a reaction without being chemically change etself

21
Q

Why is a catalyst specific to a particular reaction?

A

Because different catalysts catalyse different reactions and not all reactions have suitable catalysts.

22
Q

How do you measure rate of reaction?

A

Measure the rate at which a reactant is used up
Measure the rate at which a product is formed

23
Q

How can the rate of reaction be calculated?

A
24
Q

Tell me the conditions of a reversible reaction.

A
  1. They eventually reach an equilibrium
  2. When the rate of the forward and reverse reactions are equal = equilibrium
  3. When the concentrations of the reactants and products remain constant = equilibrium
25
Q

List the factors that affect the position of equilibrium.

A

Increasing temperature: results in a lower yield of product.
Increasing pressure
Increasing concentration
Using a catalyst: does not affect position of equilibrium but does increase the rate at which equilibrium is reached.

26
Q

What is the haber process?

A

A major process used for making ammonia

27
Q

Tell me the uses of ammonia.

A

manufacture of explosives
nitric acid
fertilisers

28
Q

How is ammonia produced?

A
29
Q

Tell me the conditions of the Haber process.

A

20000kPa
iron catalyst
450 degrees celsius

30
Q

Why are industrial conditions employed?

A

To ensure sufficient ammonia is produced at a fast enough rate

31
Q

Tell me the reactions involved in the contact process.

A

S(s) + O2(g) —> SO2(g)
2SO2(g) + O2(g) ⇌ 2SO3(g)
SO3(g) + H2O(l) —-> H2SO4(l)

32
Q

Tell me the conditions of the contact process.

A

450 degrees Celsius
Vanadium oxide catalyst
200 kPa

33
Q

What is reduction?

A

The loss of oxygen from a substance in a reaction
Gain of electrons.
Reduction in oxidation number

34
Q

What is oxidation?

A

Gain of oxygen
Loss of electrons
Increase in oxidation number

34
Q

What is an oxidising agent?

A

The substance that brings about oxidation and is reduced itself in the process

35
Q

What is the reducing agent?

A

A substance that brings about reduction and is itself oxidised during the process.

36
Q

What are spectator ions?

A

Ions that have not taken part in the reaction

IGCSE Chemistry (13 decks)

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