3.1.8 - thermodynamics

Question 1

Enthalpy change of formation (∆fHƟ)

Answer 1

the enthalpy change when 1 mole of a
compound is formed from its constituent elements in their standard
states, under standard conditions.
* E.g. 2C(s) + 3H2(g) + ½O2(g) → C2H5OH(l)

Question 2

Enthalpy change of combustion (∆cHƟ)

Answer 2

the enthalpy change when 1 mole of
a substance is completely burned in O2 under standard conditions with all
reactants + products in their standard states.
* E.g. CH4(g) + 2O2(g) → CO2(g) + 2H2O(l)

Question 3

Bond dissociation enthalpy (∆BDEHƟ):

Answer 3

the enthalpy change when 1 mole of bonds of the same type are broken under standard conditions in the gaseous state.
* E.g. Cl2(g) → 2Cl(g)

Question 4

Enthalpy change of atomisation (∆atHƟ)

Answer 4

the enthalpy change for the
formation of 1 mole of gaseous atoms from the element/compound in its
standard state.
* E.g. NaCl(s) → Na(g) + Cl(g

Question 5

First ionisation enthalpy (∆ie1HƟ)

Answer 5

enthalpy change when 1 mole of
electrons is removed from 1 mole of gaseous atoms to form one mole of
gaseous ions with a +1 charge.
* E.g. Na(g) → Na+(g) + e

Question 6

Second ionisation enthalpy (∆ie2HƟ)

Answer 6

enthalpy change when 1 mole of
electrons is removed from 1 mole of gaseous ions with a charge of +1 to
form one mole of gaseous ions with a
charge of +2.
* E.g. Na+(g) → Na2+(g) + e

Question 7

First electron affinity (∆EA1HƟ)

Answer 7

enthalpy change when 1 mole of gaseous
atoms form 1 mole of gaseous ions w/ a charge of -1.
* E.g. O(g) + e- → O-(g)

Question 8

values of first electron affinity are negative bc

Answer 8

process is exothermic

Question 9

.
Second electron affinity (∆EA2HƟ)

Answer 9

enthalpy change when 1 mole of gaseous
ions with a charge of -1 form 1 mole of gaseous ions with a charge of -2.
* E.g. O-(g) + e- → O2-(g)

Question 10

whats significant ab second electron affinity value and why is this the case

Answer 10

Values of second electron affinities are +ve as the process is
endothermic.
- This is due to the repulsion from the negative ion toward the
negative electron being added.

Question 11

Enthalpy of lattice dissociation (∆LHƟ)

Answer 11

the enthalpy change when 1 mole
of an solid ionic compound is dissociated into its constituent gaseous ions under standard conditions
* E.g. NaCl(s) → Na+(g) + Cl-(g)

Question 12

Enthalpy of lattice formation (∆LHƟ)

Answer 12

the enthalpy change when 1 mole of
an ionic compound is formed from its gaseous ions.
* E.g. Na+(g) + Cl-(g) → NaCl(s)

Question 13

Enthalpy of hydration (∆hydHƟ):

Answer 13

the enthalpy change when 1 mole of gaseous
ions is converted into 1 mole of aqueous ions.
* E.g. Na+(g) → Na+(aq)

Question 14

Enthalpy of solution (∆solHƟ)

Answer 14

the enthalpy change when 1 mole of an ionic
substance dissolves in enough solvent to form an infinitely dilute
solution.

Question 15

What can we link enthalpy of atomisation with

Answer 15

Bond dissociation enthalpy

Question 16

What 2 things must be present to link enthalpy of atomisation with bond dissociation enthalpy

Answer 16

Gaseous in its standard state and or covalently bonded in its standard state

Question 17

So enthalpy of atomisation of O =?

Answer 17

enthalpy of atomisation of O = 1/2 x bond dissociation enthalpy of O=O

Question 18

Equation for the bond dissociation enthalpy of a Cl-Cl bond is

Answer 18

Cl2(g) —> 2Cl(g)

Question 19

Equation for enthalpy of atomisation of chlorine is

Answer 19

1/2Cl2 (g) —> Cl(g)

Question 20

Equation for first electron affinity of nitrogen

Answer 20

N(g) + e- —> N-(g)

Question 21

Equation for second electron affinity of Nitrogen

Answer 21

N-(g) + e- —> N2-(g)

Question 22

Enthalpy change of solution =

Answer 22

Enthalpy change of solution = lattice diss enthalpy + sum of enthalpy of hydrations

Question 23

Lattice diss is the reverse…

Answer 23

Of lattice formation