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

Question 3

Avogadro’s number

Answer 3

The number of atoms found to be in 12g of 12C

Question 4

Empirical Formula

Answer 4

The simplest ration of atoms of each element in a compound

Question 5

Atom economy

Answer 5

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

Question 6

Homologous series

Answer 6

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

Question 7

Isomers

Answer 7

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

Question 8

Structural isomerism

Answer 8

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

Eg of structural isomerism = positional isomerism

Question 9

Chain isomerism

Answer 9

Compounds with the same molecular formula but a different carbon skeleton

Question 10

Position isomerism

Answer 10

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

Question 11

Functional group isomerism

Answer 11

Same molecular formula, different functional group

Question 12

Display structure

Answer 12

Every bond is displayed

Question 13

Stereo isomerism

Answer 13

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

Question 14

Enthalpy change of formation

Answer 14

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

Question 15

Enthalpy change of combustion

Answer 15

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 16

Standard conditions

Answer 16

298K, 1000kPa

Question 17

Mean bond enthalpy

Answer 17

The average heat needed to break one mole of covalent bonds of a molecule in a gaseous state under standard conditions

Question 18

Dynamic (in terms of equilibria)

Answer 18

Forward and reverse reactions both take place

Question 19

Equilibrium

Answer 19

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

Question 20

Catalyst

Answer 20

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 21

Activation energy

Answer 21

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

Question 22

Equilibrium constant (Kc)

Answer 22

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

Question 23

Oxidation

Answer 23

Addition of oxygen and loss of electrons to a substance

Question 24

Reduction

Answer 24

Removal of oxygen and addition of electrons to a substance

Question 25

Disproportionation

Answer 25

When atoms of the same element are simultaneously oxidised and reduced

Question 26

Reducing agent

Answer 26

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 27

Oxidising agent

Answer 27

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 28

Isotopes

Answer 28

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 29

Atomic number

Answer 29

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

Question 30

Mass number

Answer 30

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

Question 31

1st ionisation energy

Answer 31

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

Question 32

2nd ionisation energy

Answer 32

The amount of energy required to remove an electron from a gaseous 1+ ion

Question 33

Dative/Coordinate bond

Answer 33

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

Question 34

Polar molecules

Answer 34

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

Question 35

Electronegativity

Answer 35

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

Question 36

Saturated

Answer 36

When a molecule only has single bonds

Question 37

Hydrocarbon

Answer 37

A molecule containing a hydrogen and a carbon only

Question 38

Hydrolysis

Answer 38

Splitting molecules using water

Question 39

Nucleophile

Answer 39

An electron pair donator

Question 40

Electrophile

Answer 40

An electron pair acceptor

Question 41

Addition Polymerisation

Answer 41

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

Question 42

Plasticisers

Answer 42

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

Question 43

Isotatcic

Answer 43

All R groups (eg CH3) are on the same side

Question 44

Atactic

Answer 44

Random positioning of R groups (eg CH3)

Question 45

What is a free radical?

Answer 45

An atom or species with an unpaired electron

Question 46

Define standard enthalpy of atomisation

Answer 46

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

Question 47

Define first electron affinity

Answer 47

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

Question 48

Define second electron affinity

Answer 48

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