Thermodynamics Definitions

Question 1

Define Hess’s Law

Answer 1

The enthalpy change for a chemical reaction is the same, regardless of the route taken from reactants to products

Question 2

Define Standard Enthalpy of Formation

ΔH°f

Answer 2

Enthalpy change when one mole of a compound is formed from its elements under standard conditions, all reactants and products are in their standard states

Question 3

Define Standard Enthalpy of Combustion

ΔH°c

Answer 3

Enthalpy change when one mole of a compound is completely burned in oxygen under standard conditions, all reactants and products are in their standard states

Question 4

Define Standard Enthalpy of Atomisation

ΔH°at

Answer 4

Enthalpy change when one mole of gaseous atoms is formed from an element in its standard state

Question 5

Define Mean bond Enthalpy

ΔH°

Answer 5

The enthalpy change when one mole of gaseous molecules each break a covalent bond to form two free radicals, averaged over a range of compounds

Question 6

Define First Ionisation Enthalpy

1st ΔH°i

Answer 6

Standard enthalpy change when one mole of electrons is removed from one mole of gaseous atoms to give one mole of gaseous ions, each with a single positive charge

Question 7

Define Second Ionisation Enthalpy

2nd ΔH°i

Answer 7

Standard enthalpy change when one mole of electrons is removed from one mole of gaseous +1 ions to give one mole of gaseous ions, each with a 2+ charge

Question 8

Define First electron affinity

1st ΔH°ea

Answer 8

Standard enthalpy change when one mole of gasous atoms is coverted into a mole of gaseous ions, each with a single negative charge under standard conditions

Question 9

Define Second electron affinity

2nd ΔH°ea

Answer 9

Standard enthalpy change when one mole of electrons is added to a mole of gaseous ions each with a -1 charge, to form a mole of ions, each with a 2- charge

Question 10

Define Lattice Formation Enthalpy

ΔH LF°

Answer 10

Standard enthalpy change when one mole of solid ionic compound is formed from its gaseous ions

Question 11

Define Lattice Dissociation Enthalpy

ΔH LD°

Answer 11

Standard enthalpy change when one mole of solid ionic compound dissociates into its gaseous ions

Question 12

Define Standard enthalpy of hydration

ΔH hyd°

Answer 12

Standard enthalpy change when one mole of gaseous ions is coverted into one mole of aqueous ions

Question 13

Define Standard enthalpy of solution

ΔH sol°

Answer 13

Standard enthalpy change when one mole of solute dissolves in enough solvent to form a solution in which the ions are far enough apart not to interact with each other

Question 14

Contruct a balanced equation for the standard enthalpy of formation of NaCl

Answer 14

2Na(s) + Cl2(g) —> NaCl(s)

Question 15

Construct a balanced equation for the standard enthalpy of formation of CO2

Answer 15

C(s) + O2(g) —> CO2(g)

Question 16

Construct a balanced equation for the standard enthalpy of combustion of C2H6

Answer 16

C2H6(g) + 3.5O2(g) —> 2CO2(g) + 3H2O(l)

Question 17

Construct a balanced equation for the standard enthalpy of combustion of C2H5OH

Answer 17

C2H5OH(l) + 3O2(g) —> 2CO2(g) + 3H2O(l)

Question 18

Construct a balanced equation for the standard enthalpy of atomisation of Mg

Answer 18

Mg(s) —> Mg(g)

Question 19

Construct a balanced equation for the standard enthalpy of atomisation of Br2

Answer 19

1/2Br2(l) —> Br(g)

Question 20

Construct a balanced equation for the mean bond enthalpy of CH4

Answer 20

CH4(g) —> H(g) + CH3(g)

Question 21

Construct a balanced equation for the first ionisation energy of Na

Answer 21

Na(g) —> Na+(g)

Question 22

Construct a balanced equation for the first ionisation energy of Ca

Answer 22

Ca(g) —> Ca+(g)

Question 23

Construct a balanced equation for the second ionisation energy of Ca

Answer 23

Ca+(g) —> Ca2+(g) + e-

Question 24

Construct a balanced equation for the second ionisation energy of Mg

Answer 24

Mg+(g) —> Mg2+ (g) + e-

Question 25

Construct a balanced equation for the *first electron affinity* of Cl

Answer 25

Cl(g) + e- ---> Cl-(g)

Question 26

Construct a balanced symbol equation for the *first electron affinity* of S

Answer 26

S(g) + e- ---> S-(g)

Question 27

Construct a balanced equation for the *second electron affinity* of S

Answer 27

S-(g) + e- ---> S2-(g)

Question 28

Construct a balanced equation for the *second electron affinity* of O

Answer 28

O-(g) + e- ---> O2-(g)

Question 29

Construct a balanced equation for the *lattice formation enthalpy* of NaCl

Answer 29

Na+(g) + Cl-(g) ---> NaCl(s)

Question 30

Construct a balanced equation for the *lattice formation enthalpy* of MgBr2

Answer 30

Mg2+(g) + 2Br-(g) ---> MgBr2(s)

Question 31

Contruct a balanced equation for the *lattice dissociation enthalpy* of NaCl

Answer 31

NaCl(s) ---> Na+(g) + Cl-(g)

Question 32

Contruct a balanced equation for the *lattice dissociation enthalpy* of MgBr2

Answer 32

MgBr2(s) ---> Mg2+(g) + 2Br-(g)

Question 33

Construct a balanced equation for the *standard enthalpy of hydration* of Na

Answer 33

Na+(g) ---> Na+(aq)

Question 34

Construct a balanced symbol equation for the *standard enthalpy of hydration* of Cl

Answer 34

Cl-(g) ---> Cl-(aq)

Question 35

Construct a balanced equation for the *standard enthalpy of solution* of NaCl

Answer 35

NaCl(s) (+aq) ---> Na+(aq) + Cl-(aq)