Summer Exam Definitions

Question 1

Relative atomic mass

Answer 1

Average mass of an element in its ground state relative to 1/12th the mass of a carbon 12 atom

Question 2

Isotope

Answer 2

Atoms of the same element with the same no of protons and differing numbers of neutrons

Question 3

Mass number

Answer 3

No of protons and neutrons in an atom

Question 4

Radioactivity

Answer 4

Spontaneous disintegration of unstable nuclei emitting one or more types of radiation

Question 5

Half life

Answer 5

Time it takes for half the nuclei in a radioactive sample to decay

Question 6

Energy level

Answer 6

Shell which electrons of equal energy occupy

Question 7

Heisenbergs uncertainty principle

Answer 7

it is impossible to measure at the same time both the velocity and the position of an electron

Question 8

Orbital

Answer 8

Region in space around the nucleus of an atom with a high probability of finding an electron

Question 9

Atomic radius

Answer 9

Half the distance between the centre of singly bonded covalent atoms

Question 10

Electronegativity

Answer 10

Measure of attractiveness of an electron for a shared pair of electrons in a covalent bond

Question 11

First ionisation energy

Answer 11

Energy required to remove the most loosely bound electron from a neutral
gaseous atom in the ground state.

Question 12

Ionic bonding

Answer 12

Bond resulting from loss or gain of electrons

Question 13

Covalent bonding

Answer 13

Bond resulting from sharing of electrons

Question 14

Intramolecular bonding

Answer 14

Forces within molecules, e.g. polar covalent bond

Question 15

Intermolecular bonding

Answer 15

Forces between molecules, e.g. polar covalent compound like dipole dipole

Question 16

Boyles law

Answer 16

At constant temperature the volume of a fixed mass of gas is inversely and proportional to its pressure

Question 17

Charles law

Answer 17

at constant
pressure the volume of a
fixed mass of gas is
directly proportional to its temperature measured on the Kelvin scale

Question 18

Mole

Answer 18

the amount of that substance that contains 6x1023 particles.

Question 19

What do each of the following mean %w/v %v/v %w/w

Answer 19

S

Question 20

Standard solution

Answer 20

Solution of known concentration

Question 21

Primary standard

Answer 21

is a pure, stable, soluble compound from which solutions of known concentrations can be made.

Question 22

Isomer

Answer 22

Compounds with the same molecular formula but different structural formula.

Question 23

Saturated organic compound

Answer 23

Compounds which contain only single bonds between atoms.

Question 24

Hydrocarbon

Answer 24

compounds consisting of hydrogen and carbon only, bonded together covalently.

They are important as fuels and feedstock for the chemical industry.

Question 25

Heat of reaction

Answer 25

the heat change that takes place when the number of moles of reactants indicated in the balanced equation for the reaction react completely.

Question 26

Heat of combustion

Answer 26

the heat change that takes place when 1 mole of a substance is completely burned in excess oxygen.

Question 27

Heat of formation

Answer 27

the heat change that takes place when one mole of a compound in its standard state is formed from its elements in their standard states.

Question 28

Oxygenate

Answer 28

Adding Oxygenates (any fuel that contains oxygen in its molecules, eg. methanol, ethanol, MTBE (methyl tertiary butyl ether) increases octane number AND gives rise to very little pollution.

Question 29

Octane number

Answer 29

a measure of a fuels tendency to resist knocking or auto ignition. Measured on a scale of 0-100 100 being assigned to 2,2,4 trimethylpentane and 0 being assigned to heptane. i.e. if a fuel has a high octane number it will resist knocking and is therefore more desirable as a fuel.

Question 30

Rate of reaction

Answer 30

This is the change of concentration of a reactant or product per unit time.

Question 31

Activation energy

Answer 31

This is the minimum amount of energy which colliding particles must have in order to react and take place. It is the energy that must be supplied to start the chemical reaction

Question 32

Catalyst

Answer 32

a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change.

Question 33

Homogenous catalyst

Answer 33

This occurs when both the reactants and the catalysts are in the same phase e.g. Iodine snake experiment OR ethanol and ethanoic acid

Question 34

Heterogeneous catalyst

Answer 34

This occurs when the reactants and the catalysis are in a different phase (liquid vs. Solid)

Question 35

Auto ignition

Answer 35

Auto ignition causes early explosion of petrol in the car which can cause the engine to lose power