Physical Chemistry Definitions

Question 1

Atomic / Proton number

Answer 1

Number of protons in the nucleus of an atom.

Question 2

Mass / Nucleon number

Answer 2

Sum of protons and nucleus in the nucleus of an atom.

Question 3

Isotopes

Answer 3

Atoms of an element that have the same number of protons but different number of neutrons and hence different nucleon numbers.

Question 4

S orbitals

Answer 4

Orbital that is spherically symmetrical about the nucleus. The larger the principal quantum number, the orbitals get larger and more diffused.

Question 5

P orbitals

Answer 5

Three dumbbell shaped orbitals, mutually at right angles to each other. All three orbitals are degenerate, ie have the same energy.

Question 6

d orbitals

Answer 6

d orbitals have different shapes

Question 7

First Ionisation Energy

Answer 7

The energy needed to remove one mole of electrons from one mole of the gaseous atoms to form one mole of singly charged gaseous cations.

Question 8

Relative isotopic mass of an isotope

Answer 8

The mass of one atom of the isotope to 1-12th the mass of one atom of C-12 isotope

Question 9

Relative atomic mass of an element

Answer 9

The average mass of one atom of the element to 1-12th the mass of one atom of C-12 isotope

Question 10

Relative molecular mass of a substance

Answer 10

The average mass of one molecule of the substance to 1-12th the mass of one atom of C-12 isotope

Question 11

Relative formula mass of a substance

Answer 11

The average mass of one formula unit of the substance to 1-12th the mass of one atom of C-12 isotope

Question 12

One mole

Answer 12

The amount of substance which contains the same number of particles as there are atoms in exactly 12g of C-12

Question 13

Avogadro’s law

Answer 13

Equal volumes of all gases under the same conditions of temperature and pressure contain the same number of atoms/molecules.

Question 14

Empirical formula

Answer 14

The simplest formula that shows the relative number of atoms of each element present in a compound.

Question 15

Molecular formula

Answer 15

The actual number of atoms present in one molecules of the compound

Question 16

Metallic bonds

Answer 16

Strong electrostatic forces of attraction between the metal ions and the ‘sea’ of delocalised electrons in a giant metallic structure.

Question 17

Ionic bonds

Answer 17

Strong electrostatic forces of attraction between cations and anions in the crystal lattice of an ionic solid

Question 18

Covalent bond

Answer 18

Strong electrostatic forces of attraction between a shared pair of electrons and two positively charged nuclei

Question 19

Lewis Acid

Answer 19

An atom with vacant low lying orbital to accept a lone pair of electron

Question 20

Lewis base

Answer 20

An atom with a lone pair of electrons, available for donation

Question 21

Assumptions of Kinetic Theory applied to an Ideal Gas

Answer 21

Volume of gas molecules is negligible compared to the volume of the container.

Forces of attraction between the gas molecules as well as between the gas molecules and the walls of the container are negligible.

All molecular collisions are perfectly elastic. There is no loss of kinetic energy during collision.

Question 22

Enthalpy Change of Reaction

Answer 22

The amount of heat absorbed or evolved when molar quantities of reactants as shown in the chemical equation react together.

Question 23

Enthalpy Change of Formation

Answer 23

The amount of heat absorbed or evolved when one mole of a substance is formed from its constituent elements.

Question 24

Enthalpy Change of Combustion

Answer 24

The amount of heat evolved when one mole of a substance in its standard state is completely burned in excess oxygen.

Question 25

Enthalpy Change of Neutralisation

Answer 25

The amount of heat evolved when one mole of water is formed from the neutralisation between an acid and a base.

Question 26

Enthalpy Change of Atomisation

Answer 26

The amount of heat absorbed when one mole of free gaseous atoms is formed from its element.

Question 27

Bond Energy

Answer 27

The average amount of heat absorbed to break one mole of that particular bond in a particular compound in the gaseous state

Question 28

Electron Affinity

Answer 28

The amount of heat evolved when 1 mole of electrons is added to one mole of gaseous atoms to form one mole of singly negatively charged ions

Question 29

Lattice energy

Answer 29

The amount of heat evolved when one mole of the solid ionic compound is formed from its constituent free gaseous ions

Question 30

Enthalpy change of Hydration

Answer 30

The amount of heat evolved when one mole of free gaseous ions is dissolved in a large amount of water forming a solution at infinite dilution

Question 31

Enthalpy change of Solution

Answer 31

The amount of heat absorbed or evolved when one mole of a solute is dissolved in an infinite volume of water

Question 32

Hess' law

Answer 32

The enthalpy change of a chemical reaction is dependent only on the initial states of the reactants and the final state of the products and is independent of the reaction pathway taken.

Question 33

Entropy

Answer 33

The degree of disorder, of matter and ways to distribute energy in the system

Question 34

Rate equation

Answer 34

Relation of the rate of reaction to the concentration of reactants raised to the appropriate power

Question 35

Order of reaction

Answer 35

The power to which the concentration of the reactant is raised in the experimentally determined rate equation.

Question 36

Dynamic equilibrium

Answer 36

A state where the rate of forward reaction equals to the rate of backwards reaction for a reversible reaction such that there is no net change in the concentration of reactants and products

Question 37

Le Chatelier's Principle

Answer 37

If a change occurs in one of the conditions under which a reversible reaction is in dynamic equilibrium, the position of equilibrium shifts so as to minimise the change.

Question 38

Saturated solution

Answer 38

A solution containing a maximum amount of solute in a given amount of solvent such that the ions are in equilibrium with the solid

Question 39

Solubility

Answer 39

Solubility of a substance is the maximum amount of solute that dissolves in 1dm^3 of water to form a saturated solution at a stated temperature

Question 40

Arrhenius Acid

Answer 40

A substance that releases H+ ions

Question 41

Arrhenius Base

Answer 41

A substance that releases OH- ions

Question 42

Bronsted Acid

Answer 42

Proton H+ donor

Question 43

Bronsted Base

Answer 43

Proton H+ acceptor

Question 44

Definition of pH

Answer 44

-log [H+]

Question 45

Buffer solution

Answer 45

A solution where pH remains almost constant when small amounts of acid or alkali are added to it

Question 46

Suitable indicator

Answer 46

An indicator that has a working pH range which lies within the range of rapid pH change for the titration

Question 47

Standard electrode potential

Answer 47

The potential difference between a standard hydrogen electrode and the half cell in which reacting species are at molar concentrations of 1 mol dm^-3, 298k and 1bar.