3.1.8 Thermodynamics

Question 1

What is enthalpy of formation ?

Answer 1

The enthalpy change that occurs when 1 mole of a substance is formed from its constituents elements, under standard conditions, with all reactants and products being in their standard states.

Question 2

What is enthalpy of combustion ?

Answer 2

The enthalpy change needed to completely combust 1 mole of a substance with all products and reactants in their standard states under standard conditions.

Question 3

What is the Born Haber Cycle ?

Answer 3

A thermochemical cycle that includes all of the enthalpy changes involved in the formation of an ionic compound.

Question 4

What is the enthalpy of atomisation ?

Answer 4

The enthalpy of atomisation of an element is the enthalpy change that occurs when 1 mole of gaseous atoms is formed from the element inn its standard states, under standard conditions

Question 5

Give an example equation of enthalpy of atomisation with H

Answer 5

1/2 H2(g) —> H(g)

Question 6

What is enthalpy of first ionisation ?

Answer 6

The enthalpy of first ionisation is the standard enthalpy change when 1 mole of gaseous atoms is converted into a mole of gases ions each with a positive charge

Question 7

Give an example equation of enthalpy of first ionisation with Cl

Answer 7

Cl(g) —-> Cl+ + e-

Question 8

What is the lattice formation enthalpy ?

Answer 8

The lattice formation enthalpy is the. enthalpy change that occurs when 1 mole of a solid ionic lattice is formed from its gaseous ions

Question 9

Give an example of lattice formation enthalpy using Mg and O

Answer 9

Mg2+(g) + O2-(g) —-> MgO(s)

Question 10

What is the lattice dissociation enthalpy ?

Answer 10

The lattice dissociation enthalpy is the enthalpy change that occurs when 1 mole of solid ionic lattice is separated into its gaseous ions under standard conditions

Question 11

Give an example of lattice dissociation enthalpy using Na and F

Answer 11

NaF(s) —> Na+(g) + F-(g)

Question 12

What is the first electron affinity ?

Answer 12

The first electron affinity is the standard enthalpy change when a mole of electrons is added to a mole of gases atoms to form a mole of negative ions

Question 13

Give an example of first electron affinity using Cl

Answer 13

Cl(g) + e- —-> Cl-(g)

Question 14

What is the enthalpy of hydration ?

Answer 14

The enthalpy of hydration is the standard enthalpy change that occurs when water molecules surround one mole of gases ions to form one mole of aqueous ions.

Question 15

Give an example of enthalpy of hydration using K

Answer 15

K+(g) + aq —-> K+(aq)

Question 16

What is the enthalpy of solution ?

Answer 16

The enthalpy of solution is the standard enthalpy change that occurs when 1 mole of solute dissolves completely in sufficient solvent to form a solution in which the molecules of each ion are sufficiently far apart so as not to interact with each other

Question 17

Give an example of enthalpy of solution using Li and Br

Answer 17

LiBr(s) + aq —-> Li+(aq) + Br-(aq)

Question 18

What is the bond dissociation enthalpy?

Answer 18

The bond dissociation enthalpy (mean bond enthalpy) is the standard enthalpy change that occurs when 1 mole of gasses molecules each breaks a covalent bond to form 2 gases free radicals, averaged over a range of compounds

Question 19

Give an example of bond dissociation enthalpy using H

Answer 19

H2(g) —-> 2H(g)

Question 20

State the meaning of the word enthalpy change ?

Answer 20

Heat (energy) change at constant pressure

Question 21

What does the perfect ionic model assume ?

Answer 21

• That all ions are perfectly spherical
• The ions display no covalent character