Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Physical Chemistry A2 > Thermodynamics > Flashcards

Thermodynamics Flashcards

a2 chem

You may prefer our related Brainscape-certified flashcards:
AP® Chemistry flashcards Periodic Table flashcards Chemistry 101 flashcards Organic Chemistry 101 flashcards
1
Q

Enthalpy change definiton

A

Heat energy change at constant pressure.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Enthalpy of formation definition

A

Enthalpy change when one mole of a substance is formed from its constituent elements with all substances in their standard states. EXOTHERMIC

H2(g) + ½ O2(g) →H2O(l)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Enthalpy of combustion definition

A

Enthalpy change when one mole of a substance undergoes complete combustion in oxygen with all substances in standard states.
EXOTHERMIC

CH4(g) + 2O2(g) →CO2(g) + 2H2O(l))

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Enthalpy of neutralisation definition

A

Enthalpy change when 1 mole of water is formed in a reaction between an acid and alkali under standard conditions
EXOTHERMIC

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Enthalpy of atomisation definition

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

First ionisation energy definition

A

Enthalpy change when each atom in one mole of gaseous atoms loses one electron to form one mole of gaseous 1+ ions.

Mg(g) →Mg+(g) + e-

ENDOTHERMIC

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Second ionisation energy definition

A

Enthalpy change when each ion in one mole of gaseous 1+ ions loses one electron to form one mole of gaseous 2+ ions.

Mg+(g) →Mg2+(g) + e-
ENDOTHERMIC

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

First electron affinity definition

A

Enthalpy change when each atom in one mole of gaseous atoms gains one electron to form one mole of gaseous 1– ions.

O(g) + e- → O-(g)
EXOTHERMIC

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Second electron affinity definition

A

Enthalpy change when each ion in one mole of gaseous 1– ions gains one electron to form one mole of gaseous 2– ions.

O-(g) + e- → O2-(g)
ENDOTHERMIC

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Lattice enthalpy of formation definition

A

Enthalpy change when one mole of a solid ionic compound is formed from into its constituent ions in the gas phase.

Na+(g) + Cl- (g) → NaCl(s
EXOTHERMIC

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Lattice enthalpy of dissociation definition

A

Enthalpy change when one mole of a solid ionic compound is broken up into its constituent ions in the gas phase
ENDOTHERMIC

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Enthalpy of hydration definition

A

Enthalpy change when one mole of gaseous ions become hydrated (dissolved in water).

Na+(g) + aq → Na+(aq
EXOTHERMIC

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Enthalpy of solution definition

A

Enthalpy change when one mole of an ionic solid dissolves in an amount of water large enough so that the dissolved ions are well separated and do not interact with each other.

NaCl(s) + aq → Na+(aq) + Cl-(aq)
ENDO/EXO

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Bond dissociation enthalpy definition

A

Enthalpy change when one mole of covalent bonds is broken in the gaseous state.
ENDOTHERMIC

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Mean bond enthalpy definition

A

Enthalpy change when one mole of gaseous molecules each breaks a covalent bond to form two free radicals, averaged over a range of compounds.

CH4 (g) → C(g) + 4H(g) = +1664kJ mol-1 / 4

ENDO/EXO

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Enthalpy of vaporisation definition

A

Enthalpy change when one mole of a liquid is turned into a gas
ENDOTHERMIC

17
Q

Enthalpy of fusion definition

A

Enthalpy change when one mole of a solid is turned into a liquid
ENDOTHERMIC

18
Q

How to draw a born-haber cycle?

A

1) Start with solid on bottom line

2)Enthalpy of formation ( writing the elements in their standard states)

3)enthalpy of atomisation of the elements ( one mole of gaseous atoms)

4) ionisation energy (mainly metal first)

5) 2nd ionisation energy/affinity depending on the q’s

19
Q

What areas of born-haber cycle are negative?

A

enthalpy of formation (bottom left)

(left hand side)

20
Q

How is a lattice enthalpy calculated?

A

using a born-haber cycle

21
Q

what determines the theoretical and experimental values of a lattice enthalpy?

A

it depends on how purely ionic the compound is.

22
Q

What can data referring to a perfectly ionic model assume?

A

the theoretical lattice enthalpy

23
Q

What makes a perfect ionic model perfect?

A
  • Ions that are perfectly spherical
  • The charge is evenly distributed in this sphere (point charges)
24
Q

Why is the experimental value different from the theoretical value of lattice enthalpy?

A
  • Suggests that the compound being experimented on doesn’t follow the perfectly ionic model and has covalent characteristics.
  • The positive ion distorts the charge distribution in the negative ion ( positive ion polarises the negative ion)
25
Q

What does more polarisation indicate?

A

The more covalent character there will be

26
Q

What can lattice enthalpy values tell us?

A

How much a substance is ‘purely ionic’

27
Q

What does bigger lattice enthalpy suggest?

A

more polarisation so the greater the covalent character in compound.

28
Q

What process occurs when enthalpy change of solution and when can it happen?

A

The ionic lattice (in solid form) reacts with water to form free moving ions.

There are new bonds formed between ions and water.

The ions are hydrated.

It can only happen if the new bonds formed are the same strength or greater than those broken. If this isn’t the case then it’s very unlikely to dissolve. Soluble substances tend to have exothermic enthalpies of solution for this reason.

29
Q

What is entropy?

A

Entropy is the measure of disorder in a system. Its the number of ways energy can be shared out between particles.

30
Q

What does more disorder indicate about the level of entropy?

A

The more disorder the higher the level of enthalpy.

31
Q

what are the levels of disorders in solids, liquids and gases?

A

solids have the lowest level of disorder as particles are arranged in rows.

Liquids and gases are more disordered.

32
Q

What factor affects entropy change?

A

The number of particles also affect entropy change. If there is an increase in moles then entropy increases as there are more ways for energy to be distributed.

33
Q

Increasing entropy is….

A

energetically favourable and some reactions that are enthalpically unfavourable (endothermic) can still spontaneously react of changes in entropy overcome changes in enthalpy.

34
Q

What type of reaction is enthalpically unfavourable?

A

Endothermic reactions

35
Q

What type of reaction is entropically favourable?

A

When there is an increase in moles from reactants –> products

when the state of product changes to one of increased disorder

36
Q

How to calculate enthalpy of solution?

A
  • using a hess cycle basically

down arrow from breaking up solid lattice ( enthalpy of lattice dissociation)

up arrow when gaseous ions are dissolved in water (enthalpy of hydration)

37
Q

What is the Gibbs free energy equation and what does it tell us?

A

It tells us if a reaction is feasible or not.

ΔG=ΔH-TΔS

Gibbs free energy = Enthalpy change (mol-1) - temperature (k) x entropy change (jk-1mol-1)

38
Q

What makes a reaction feasible in theory?

A

If ΔG (Gibbs free energy) is negative or 0

39
Q

What is the rearranged equation and method to calculate temperature of which a reaction becomes feasible?

A

T= ΔH/ ΔS

Calculate entropy change ΔS:

S.Products- S.reactants

Physical Chemistry A2 (5 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions