Energetics Definitions

Question 1

Heat

Answer 1

A form of energy that flows from something at a higher temperature to something at a lower temperature

Question 2

Temperature

Answer 2

A measure of the average kinetic energy of particles

Question 3

Internal energy

Answer 3

The total amount of energy (kinetic and potential) in a sample of a substance

Question 4

Exothermic

Answer 4

Heat energy is transferred from the system (chemical reaction) to the surroundings - surroundings get hotter

Question 5

Endothermic

Answer 5

A system (chemical reaction) takes in heat energy from the surroundings - surroundings get cooler

Question 6

Enthalpy change

Answer 6

The heat energy exchanged with the surroundings at constant pressure

Question 7

Stability

Answer 7

Refers to the relative energies of the reactants and products. If the products are at a lower enthalpy than the reactants, then they are more stable

Question 8

Standard conditions

Answer 8

A common set of conditions used to compare enthalpies: 100kPa, 1mol/dm3, 298K if not specified

Question 9

Standard enthalpy change of reaction

Answer 9

The enthalpy change when molar amounts of reactants, as shown stoichiometric equation, react together under standard conditions

Question 10

Standard enthalpy change of combustion

Answer 10

The enthalpy change when one mole of a substance is burnt completely in oxygen under standard conditions

Question 11

Specific heat capacity

Answer 11

The energy needed to raise the temperature of 1g of a substance by 1K (1°C)

Question 12

Enthalpy change of neutralisation

Answer 12

Enthalpy change when one mole of water molecules are formed when an acid (H+) reacts with an alkali (OH-) under standard conditions

Question 13

Enthalpy change of solution

Answer 13

The enthalpy change when one mole of a solute is dissolved in excess solvent to form a solution of infinite dilution under standard conditions

Question 14

Hess’ Law

Answer 14

The enthalpy change accompanying a chemical reaction is independent of the pathway between initial and final states

Question 15

Standard enthalpy change of formation

Answer 15

The enthalpy change when one mole of a substance is formed from is elements in their standard states under standard conditions

Question 16

Standard state

Answer 16

The pure substance at 100kPa and a specified temperature (298K if not specified)

Question 17

Bond enthalpy

Answer 17

The enthalpy change when one mole of covalent bonds in a gaseous molecule are broken under standard conditions

Question 18

Standard enthalpy change of vaporisation

Answer 18

The energy needed to convert one mole of a liquid into vapour under standard conditions

Question 19

Average bond enthalpy

Answer 19

The average amount of energy required to break one mole of covalent bonds in gaseous molecules under standard conditions

Question 20

First ionisation energy

Answer 20

The enthalpy change when one electron is removed from each atom in one mole of gaseous atoms under standard conditions

Question 21

First electron affinity

Answer 21

The enthalpy change when one electron is added to each atom in one mole of gaseous atoms under standard conditions

Question 22

Lattice enthalpy

Answer 22

The enthalpy change when one mole of an ionic compound is split into its constituent gaseous ions under standard conditions

Question 23

Born Haber Cycle

Answer 23

An energy level diagram breaking down the formation of an ionic compound into a series of simpler steps

Question 24

Enthalpy change of hydration

Answer 24

The enthalpy change when one mole of gaseous ions is surrounded by water molecules to form an infinitely dilute solution under standard conditions

Question 25

Entropy

Answer 25

A measure of how available energy is distributed among the particles

Question 26

Spontaneous reaction

Answer 26

One that occurs without any outside influence

Question 27

Free energy change

Answer 27

Is related to the entropy change of the Universe and can be defined using the equation:
DeltaG=T x DeltaS
For a reaction to be spontaneous, DeltaG must be negative. DeltaG° is standard free energy change