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Chemistry GCSE OCR Gateway > C3 Chemical Reactions > Flashcards

C3 Chemical Reactions Flashcards

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1
Q

Why is the formula for Bromine Br2 and not Br?

A

Bromine exists as a diatomic molecule

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2
Q

What is the meaning of the Roman Numerals in Iron(II) and Iron (III)?

A

The number of electrons in its outer shell

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3
Q

Explain why a wooden log has more mass before burning than the ashes it leaves after burning despite the Law of Conservation of Mass?

A

Some of the particles will have evaporated as a gas. If the reaction took place in a closed system, the mass would be the same.

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4
Q

Explain, in terms of particles, why iron bars increase in mass after rusting.

A

Rust is the reaction between Iron and Oxygen - since there are now more particles since the oxygen has bonded to the iron, the mass is higher.

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5
Q

Explain why an unbalanced chemical equation is not a completed chemical equation.

A

It does not abide to the Law of Conservation of Mass - the number of particles is not the same on both sides of the equation.

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6
Q

What is a half-equation?

A

An equation to model what happens to one reactant in a chemical equation and its electrons

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7
Q

What is a complete ionic equation ?

A

An ionic equation with all of the ions in the experiment present.

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8
Q

What are spectator ions?

A

Ions that do not take part in the reaction (i.e. that are the same on both sides of the equation)

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9
Q

What is a net ionic equation?

A

An ionic equation only showing the ions that change in the reaction (i.e. ignoring spectator ions)

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10
Q

What is the value of Avogrado’s Constant?

A

6.02x10^23

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11
Q

What is the mole?

A

The amount of any substance that has the same number of entities as there are atoms in Carbon-12

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12
Q

What is the mass of one mole of a substance?

A

Its relative formula mass/relative atomic mass/molar mass

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13
Q

What is the equation linking mass, moles and molar mass?

A

Mass (g) = moles (mol) x molar mass (g/mol)
OR
Moles (mol) = Mass (g) / molar mass (g/mol)

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14
Q

What is a limiting reactant?

A

The reactant that detemines how much product is produced.

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15
Q

What is a reactant that is in excess?

A

There are more moles of the reactant in excess than the limiting reactant, so it has no effect on how much product is produced.

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16
Q

How do you work out which is the limiting reactant?

A

Calculate the number of MOLES of each substance - NEVER use the MASS

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17
Q

What is the stoichiometry of an equation?

A

The relative amounts of each substance used.

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18
Q

What is an endothermic reaction?

A

A reaction that takes in energy from the surroundings.

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19
Q

What is an exothermic reaction?

A

A reaction that releases energy to the surroundings.

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20
Q

What are some examples of exothermic reactions?

A

Combustion
Neutralisation

21
Q

What are some examples of endothermic reactions?

A

Thermal decomposition
Photosynthesis

22
Q

Does breaking bonds release or require energy?

A

Breaking bonds requires energy.

23
Q

Does making bonds release or require energy?

A

Making bonds releases energy.

24
Q

What is the formula for energy change?

A

Energy change = energy required to break bonds of reactants - energy released when making bonds

25
Q

Is the energy change of an endothermic reaction positive or negative?

A

Positive because more energy is required to break bonds than to make them, so energy is taken from the surroundings.

26
Q

Is the energy change of an exothermic reaction positive or negative?

A

Negative because more energy is released making bonds than is required to break bonds, so energy is released to the surroundings.

27
Q

What are bond energies?

A

The energy required to break 1 mol of a particular bond.
OR
The energy released when 1 mol of this bond is made

28
Q

What is oxidation?

A

The gain of oxygen
OR
The loss of electrons
OR
Both

29
Q

What is reduction?

A

The loss of oxygen
OR
The gain of electrons
OR
Both

30
Q

What is a redox reaction?

A

A reaction where reduction and oxidation happen at the same time.

31
Q

What is an oxidising agent?

A

A substance that oxidises another substance without getting oxidised itself.

32
Q

What is a reduction agent?

A

A substance that reduces another substance without getting reduced itself.

33
Q

What is an acid?

A

A substance that releases hydrogen ions when it dissolves in water to form a solution

34
Q

What is a base?

A

A substance that can neutralise an acid?

35
Q

What is an alkali?

A

A base that can dissolve in water. AN alkali releases hydroxide ions when it dissolves in water to form a solution.

36
Q

What is the pH scale?

A

A scale displaying the acidity or the alkalinity of a substance. 0-6 is acidic, 8-14 is alkaline and 7 is neutral. The closer to 0 you go, the more acidic the substance becomes. The closer to 14 you go, the more alkaline it becomes.

37
Q

How can you find the pH of a solution?

A

Using indicators e.g. Universal Indicator or an electronic probe.

38
Q

What is the general equation for neutralisation?

A

Acid + base —> salt + water

39
Q

What is neutralisation?

A

The process where an acid and a base react to form a salt and water. The salt made depends on the acid and the base used.

40
Q

How can you predict the salt made in a neutralisation reaction?

A

The first part comes from the metal in the base/alkali and the second part comes from the acid used e.g. Sodium Hydroxide + Nitric Acid makes Sodium Nitrate.

41
Q

Why are all alkalis bases but all bases are not alkalis?

A

A base is a substance that neutralises an acid, whereas an alkali is a base that can also dissolve in water.

42
Q

What is the general equation for the reaction between an acid and a carbonate?

A

Acid + carbonate —> salt + water + carbon dioxide

43
Q

What is the general equation for the reaction between an acid and a metal?

A

Acid + metal —> salt + hydrogen

44
Q

What is the difference between a dilute and concentrated acid>

A

A dilute acid has a low acid-to-volume ratio - a concentrated acid has a high acid-to-volume ratio e.g. dilute acid: 1: 10, concentrated acid: 12:10

45
Q

What is the difference between weak and strong acids?

A

Weak acids are only partially ionised - only some of their molecules release hydrogen ions. Strong acids are completely ionised - all of their molecules release hydrogen ions.

46
Q

Explain why a dilute strong acid may have the same pH as a concentrated weak acid.

A

pH depends on both concentration and the strength of the acid. A strong acid will have a low pH but that will increase due to it being diluted. A weak acid will have a higher pH but that will decrease because it is concentrated.

47
Q

What is electrolysis?

A

A process where an electric current is passed through a compound, causing a chemical change.

48
Q

What components are required for electrolysis?

A

Electrolyte: A compound in a liquid state or in a solution, which contains mobile (able to move) ions and can conduct electricity.
Electrodes: Two are required. Made from a metal or graphite that conducts electricity to the electrolyte.
An electrical supply.

Chemistry GCSE OCR Gateway (4 decks)

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