T8 + 13: Energetics I & II

Question 1

Standard enthalpy change of reaction

Answer 1

enthalpy change when molar quantities stated in the equation react together under standard conditions

Question 2

Standard enthalpy change of formation

Answer 2

enthalpy change when one mole of a compound is formed from its constituent elements in their standard states under standard conditions

always 0 for an element

Question 3

Standard enthalpy change of combustion

Answer 3

enthalpy change that occurs when one mole of a substance is
combusted completely in oxygen under standard conditions.

Question 4

Standard enthalpy change of neutralisation

Answer 4

enthalpy change when solutions of an acid and an alkali react together under standard conditions to produce 1 mole of water

Question 5

First ionisation energy

Answer 5

the enthalpy change when one mole of electrons are removed from one mole of gaseous atoms to form gaseous 1+ ions

Question 6

Mean bond enthalpy

Answer 6

the enthalpy needed to break the covalent bond into gaseous atoms, averaged over different molecules

only applies if substances start and end in gaseous state

Question 7

Standard conditions

Answer 7

• 100 kPa pressure
• 298 K (room temperature or 25oC)
• Solutions at 1mol dm-3
• all substances should have their normal state at 298K

Question 8

Hess’ Law

Answer 8

total enthalpy change for a reaction is independent of the route by which the chemical change takes place

Question 9

Standard enthalpy of atomisation

Answer 9

the amount of energy required to produce one mole of gaseous atoms from an element in its standard state under standard conditions

Question 10

First electron affinity

Answer 10

the enthalpy change that occurs when 1 mole of gaseous atoms gain 1 mole of electrons to form 1 mole of gaseous ions with a –1 charge

Question 11

Second electron affinity

Answer 11

the enthalpy change when one mole of gaseous 1- ions gains one electron per ion to produce gaseous 2- ions

Question 12

Lattice enthalpy

Answer 12

the standard enthalpy change when 1 mole of an ionic crystal lattice is formed from its constituent ions in gaseous form

Question 13

Enthalpy change of solution

Answer 13

the enthalpy change when one mole of substance in its standard state is dissolved in water to form a solution where the ions are far enough apart not to interact, under standard conditions

Question 14

Enthalpy change of hydration

Answer 14

the enthalpy change when one mole of gaseous ions dissolves in water to form one mole of aqueous ions.

Question 15

Lattice enthalpy of formation

Answer 15

the standard enthalpy change when 1 mole of an ionic crystal lattice is formed from its constituent ions in gaseous form.

Question 16

Lattice enthalpy of dissociation

Answer 16

the enthalpy change when one mole of an ionic compound is split up into its constituent gaseous ions. (it will always be endothermic)

Question 17

entropy

Answer 17

disorder in a system

Question 18

how to work out entropy of a system

Answer 18

entropy of products - entropy of reactants

Question 19

+ve entropy =?

Answer 19

more moles of products and harder change of state (solid –> gas > solid –> liquid)

Question 20

how to work out entropy of surroundings

Answer 20

-ΔH / T

Question 21

how to work out total entropy?

Answer 21

entropy of system + entropy of surroundings