Thermodynamics

Question 1

What is enthalpy of formation

Answer 1

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

Question 2

Is enthalpy of formation exo or endothermic

Answer 2

It is exothermic

Question 3

What is enthalpy of atomisation

Answer 3

Enthalpy change for the formation of one mole of gaseous atoms from elements in their standard state

Question 4

What is the equation for enthalpy of atomisation of Na (state what type of bond is broken)

Answer 4

Na(s) —> Na(g)
( metallic bonds broken

Question 5

What is the enthalpy of atomisation equation for Cl (state what type of bond is broken)

Answer 5

1/2Cl2(g) —> Cl(g)
Intermolecular forces broken

Question 6

What is first ionisation energy

Answer 6

X(g) —> X+ + e-

Question 7

Is ionisation energy an exothermic or endothermic reaction

Answer 7

It is endothermic

Question 8

Why is ionisation energy endothermic

Answer 8

Because energy is required to overcome the electrostatic force of attraction between the nucleus of the atom and the electron being removed

Question 9

Explain why successive ionisation energies are more endothermic

Answer 9

It is harder to remove an electron from a more positive ion
Electron that is being removed is closer to the nucleus therefore more strongly attracted

Question 10

What is the equation for 1st elctron affinity

Answer 10

X(g) + e- –> X-(g)

Question 11

Is 1st electron affinity exo or endothermic

Answer 11

Exothermic

Question 12

Explain why 1st electron affinity has a negative ΔH

Answer 12

There is a net attractive force between the nucleus of the atom and the electron added therefore energy is released

Question 13

What is the equation for second electron affinity

Answer 13

X-(g) + e- –> X2-(g)

Question 14

Explain why second electron affinity and and successive energy affinities are endothermic

Answer 14

Repulsion between the negative ion and electron
Therefore energy is required to overcome repulsion

Question 15

State a trend in successive electron affinities

Answer 15

They get progressively more endothermic

Question 16

What is Lattice dissociation

Answer 16

The standard enthalpy change for the dissociation of one mole of a solid ionic lattice into its gaseous ions

Question 17

What is the general formula for lattice dissociation

Answer 17

MX(s) —> M+(g) + X-(g)

Question 18

What is the symbol for lattice dissociation

Answer 18

ΔHL

Question 19

What is the symbol for electron affinity

Answer 19

ΔHea

Question 20

What is the symbol for ionisation energy

Answer 20

ΔHi

Question 21

What is the symbol for enthalpy of atomisation

Answer 21

ΔHat

Question 22

What is the symbol for enthalpy of formation

Answer 22

ΔHf

Question 23

What is enthalpy of solution

Answer 23

Enthalpy change for: MX(s) —-> M+ (aq) + X-(aq)

Question 24

What is enthalpy of hydration

Answer 24

Enthalpy change for X+/-(g) ——> X+/-(aq)

Question 25

Draw a solution Hess cycle for Nacl

Answer 25

-

Question 26

What is in the top left of a solution Hess cycle

Answer 26

Compound in solid state

Question 27

What is at the bottom of a solution Hess cycle

Answer 27

Ions in gaseous state

Question 28

What is in the top right of a solution Hess cycle

Answer 28

Ions in aqueous state

Question 29

What does the arrow going from the compound to gaseous ions represent in a solution Hess cycle

Answer 29

Enthalpy of lattice dissociation

Question 30

What do the arrows going from gaseous ions to aqueous ions represent in a solution Hess cycle

Answer 30

Enthalpy of Hydration

Question 31

What does the arrow going from the solid ionic compound to aqueous ions represent in a solution Hess cycle

Answer 31

Enthalpy of solution

Question 32

What does the arrow going from the solid ionic compound to aqueous ions represent in a sol

Question 33

What is the equation for enthalpy of solution

Answer 33

Enthalpy of lattice dissociation + Enthalpy of hydration positive ion + enthalpy of hydration of negative ion

Question 34

What affects the value of enthalpy of lattice formation/dissociation

Answer 34

Smaller & highly charged ions have a higher charge density - giving stronger electrostatic force of attraction between oppositely charged ions Gives more exo value for formation Gives more enforcing value for dissociation

Question 35

What affects the value of enthalpy of hydration for positive ions

Answer 35

The force of attraction between the delta negative O of water, and the positive ion

Question 36

What causes a stronger force of attraction between a delta negative oxygen on a water molecule and a positive ion (how does it affect the value of enthalpy of hydration)

Answer 36

Smaller more positive ions will have a higher charge density Will attract delta H oxygen on H2O stronger Which gives a more exothermic value for enthalpy of hydration

Question 37

What affects the value of enthalpy of hydration for negative ions

Answer 37

The attraction between the delta positive H on a H2O molecule and the negative ion

Question 38

What affects the attraction between delta positive H on a water molecule and a negative ion (how does it affect the value of enthalpy of hydration)

Answer 38

Smaller more negative ions will have a larger charge density This will attract the delta positive H on the H2O stronger This gives a more exothermic value for enthalpy of hydration

Question 39

When is covalent character more prevalent

Answer 39

The more charge dense the positive ion is, as well as when there is a larger or more negative, negative ion. (n+ more polarising, n- more polarisable)

Question 40

When does the most covalent character occur

Answer 40

When we have small, highly positive ions are bonded to large, highly negative ions

Question 41

What does the perfect ionic model assume

Answer 41

Assumes that the ions are perfect spheres (no covalent character)

Question 42

When will the born barber value for enthalpy of lattice F/D be similar to the value from the PIM equation

Answer 42

When there is no/little covalent character

Question 43

If there is covalent character present, how will the born haber value differ from the P.I.M value for lattice enthalpy of F/D

Answer 43

The value will typically be larger Either more -ve for lattice enthalpy of dissociation Or more +ve for lattice enthalpy of formation

Question 44

What is bond enthalpy

Answer 44

The amount of energy required to break one mole of a specific covalent bond in the gas phase

Question 45

What's the equation for delta S

Answer 45

SUM OF ∆SPRODUCTS - SUM OF ∆S REACTANTS

Question 46

What's the equation for delta g

Answer 46

∆G = ∆H - T∆S