Definitions - All Topics

Question 1

Relative Atomic Mass (AR).

Answer 1

The average mass of an atom of an element compared to 1/12th of the mass of a 12C atom

Question 2

Relative Molecular Mass (MR)

Answer 2

The average mass of a molecule compared to 1/12th of the mass of a 12C atom

Question 3

Empirical Formula

Answer 3

The simplest ration of atoms of each element in a compound

Question 4

Atom economy

Answer 4

Measure of what proportion of the product of a reaction is desired, and how much is waste

Question 5

Homologous series

Answer 5

A group of chemicals which have similar chemical properties, the same functional group and can be represented by a general formula

Question 6

Isomers

Answer 6

Chemicals with the same molecular formula, but a different structural formula

Question 7

Structural isomerism

Answer 7

Compounds with the same molecular formula, but different structural/skeletal/displayed formula.

Eg of structural isomerism = positional isomerism

Question 8

Chain isomerism

Answer 8

Compounds with the same molecular formula but a different carbon skeleton

Question 9

Position isomerism

Answer 9

Compounds with the same molecular formula and carbon skeleton, but a different position of the same type of functional group

Question 10

Functional group isomerism

Answer 10

Same molecular formula, different functional group

Question 11

Stereo isomerism

Answer 11

When molecules have the same structural formula but a different spatial arrangement of atoms

Question 12

Enthalpy change of formation

Answer 12

The enthalpy change when one mole of a substance is formed from its elements with all products and reactants in their standard states under standard conditions

Question 13

Enthalpy change of combustion

Answer 13

The enthalpy change when one mole of a substance is burned completely in oxygen with all reactants and products in their standard states under standard conditions

Question 14

Standard conditions

Answer 14

298K, 100kPa, 1 moldm^-3 if any solutions involved

Question 15

Mean bond enthalpy

Answer 15

The average heat needed to break one mole of covalent bonds of a molecule in a gaseous state under standard conditions, averaged over a range of compounds

Question 16

Define “dynamic” (in terms of equilibria)

Answer 16

Forward and reverse reactions both take place

Question 17

Equilibrium

Answer 17

Both forward and reverse reactions take place at equal rates. The concentration of all reactants remain constant

Question 18

Catalyst

Answer 18

A substance that increases the rate or reaction without being changed in chemical composition or amount. They work by providing an alternative pathway/reaction route of lower activation energy

Question 19

Activation energy

Answer 19

The minimum amount of energy needed for a reaction to occur/for a successful collision

Question 20

Equilibrium constant (Kc)

Answer 20

A value calculated from the equilibrium concentrations for a system at constant temperature

Kc = concentration of products/concentration of reactants

Question 21

Oxidation

Answer 21

Addition of oxygen or loss of electrons to a substance

Question 22

Reduction

Answer 22

Removal of oxygen or addition of electrons to a substance

Question 23

Disproportionation

Answer 23

When atoms of the same element are simultaneously oxidised and reduced

Question 24

Reducing agent

Answer 24

A species which aids the reduction of another species by donating the electrons which the other species gains. The reducing agent’s oxidation state will become more positive (more oxidised)

Question 25

Oxidising agent

Answer 25

A species which aids the oxidation of another species by accepting the electrons that the other species loses. The oxidising agent's oxidation state will become less positive/more negative (more reduced)

Question 26

Isotopes

Answer 26

Atoms of the same element with the same atomic number but a different mass number. (same no. of protons and electrons, diff. no. of neutrons)

Question 27

Atomic number

Answer 27

The number of protons in the atom nucleus (aka protonic no.)

Question 28

Mass number

Answer 28

The number of protons AND neutrons in the nucleus of an atom

Question 29

1st ionisation energy

Answer 29

The energy needed to remove 1 mole of electrons from 1 mole of gaseous atoms

Question 30

2nd ionisation energy

Answer 30

The amount of energy required to remove an electron from each ion in 1 mole of gaseous 1+ ions

Question 31

Dative/Coordinate bond

Answer 31

A covalent bond whereby the pair of electrons originate from one atom

Question 32

Polar molecules

Answer 32

Molecules whereby the polar bonds combine in such a way some parts are more negative/positive

Question 33

Electronegativity

Answer 33

The power of an atom to attract the pair of electrons in a covalent bond

Question 34

Saturated

Answer 34

When a molecule contains only carbon-carbon single bonds (no double bonds)

Question 35

Hydrocarbon

Answer 35

A molecule containing a hydrogen and a carbon only

Question 36

Hydrolysis

Answer 36

Splitting molecules using water

Question 37

Nucleophile

Answer 37

An electron pair donator

Question 38

Electrophile

Answer 38

An electron pair acceptor

Question 39

Addition Polymerisation

Answer 39

Formation of long chain molecules from lots of small molecules joining together with no other products

Question 40

Plasticisers

Answer 40

Small molecules that get between the polymer chains, allowing them to slide past each other. This makes the chains more flexible

Question 41

What is a free radical?

Answer 41

An atom or species with an unpaired electron

Question 42

Define standard enthalpy of atomisation

Answer 42

The enthalpy change when mole of gaseous atoms is formed from the element in its standard state under standard conditions

Question 43

Define first electron affinity

Answer 43

The enthalpy change when one mole of gaseous atoms is converted into one mole of gaseous ions, each with a single negative charge, under standard conditions

Question 44

Define second electron affinity

Answer 44

The enthalpy change when mole of electrons is added to one mole of gaseous ions, each with a single negative charge to form one mole of gaseous ions each with 2 negative charges