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Chemistry A level > 1.8 Thermodynamics > Flashcards

1.8 Thermodynamics Flashcards

1
Q

What does Hess’s law state

A

The enthalpy change for a reaction is independent of the route taken

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2
Q

Define standard enthalpy of formation

A

The enthalpy change when one mole of a compound is formed from its elements under standard conditions in its standard states

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3
Q

Whats the standard enthalpy of an element

A

0

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4
Q

Define standard enthalpy of combustion

A

The enthalpy change when one mole of a substance is burnt completely in excess oxygen

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5
Q

Define standard enthalpy of atomisation

A

Enthalpy change when one mole of gaseous atoms is formed from a compound in its standard state in standard conditions

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6
Q

Define first ionisation energy

A

Enthalpy change when one mole of electrons is removed from one mole of gaseous atoms to form one mole of gaseous 1+ ions

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7
Q

Define second ionisation energy

A

Enthalpy change when one mole of electrons is removed from one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions

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8
Q

Define first electron affinity

A

Enthalpy change when one mole of gaseous atoms gains one mole of electrons to form one mole of gaseous 1- ions

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9
Q

Define second electron affinity

A

Enthalpy change when one mole of gaseous 1- ions gains one mole of electrons to form one mole of gaseous 2- ions

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10
Q

Define lattice enthalpy of formation

A

Enthalpy change when one mole of solid ionic lattice is formed from its gaseous ions

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11
Q

Define lattice enthalpy of dissociation

A

Enthalpy change when one mole of solid ionic lattice is dissociated into its gaseous ions

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12
Q

Define enthalpy of hydration

A

Enthalpy change when one mole of gaseous ions become hydrated in water to infinite dilution

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13
Q

Define enthalpy of solution

A

Enthalpy change when one mole of solute dissolves completely in a solvent to infinite dilution

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14
Q

Define mean bond dissociation enthalpy

A

Enthalpy change when one mole of covalent bonds is broke, with all species in the gaseous state

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15
Q

What factors effect the lattice enthalpy of an ionic compound

A

Size of ions
Charge on the ions

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16
Q

How can you increase lattice enthalpy and why

A

Smaller ions - charge centres will be closer together
Increased charge - greater electrostatic FOA between oppositely charted ions

17
Q

How can born haber cycles be used to see if compounds could theoretically exist

A

Use known data to predict certain values and see if they would be thermodynamically stable

18
Q

What happens when a solid is dissolved in terms of interactions of ions with water

A

Break lattice –> gaseous ions, dissolve in water. Aqueous ions are surrounded by water molecules which have a permanent dipole due to polar O-H bond

19
Q

What is the perfect ionic model

A

Assumes that ions are perfectly spherical and that there is an even charge distribution

20
Q

Define the terms spontaneous and feasible

A

If a reaction is spontaneous and feasible, it will take place of its own accord

21
Q

Is a reaction with a positive or negative enthalpy change more likely to be spontaneous

A

negative - exothermic

22
Q

Define entropy

A

Randomness/disorder of a system
Higher value = more disordered

23
Q

What units is entropy measured in

A

JK-1mol-1

24
Q

What is the second law of thermodynamics

A

Entropy always increases, as it is overwhelmingly more likely for molecules to be disordered than ordered

25
Q

Is a reaction with positive or negative entropy more likely to be spontaneous

A

positive - reactions always try and increase the amount of disorder

26
Q

Compare the general entropy values for solids, liquids and gases

A

Solids < liquids < gases

27
Q

How would you calculate the entropy change for a reaction

A

Entropy change = sum of products entropy - sum of reactants entropy

delta S = delta S (products) - delta S (reactants)

28
Q

Define gibbs free energy using an equation

A

Delta G = delta H - T Delta S

Gibbs free energy = enthalpy change - temperature x entropy change

29
Q

What does the value for gibbs free energy for a reaction show

A

If G<0 reaction is feasible
If G = 0 reaction is JUST feasible
If G > 0 reaction isnt feasible

30
Q

What is the significance of the temperature at which G = 0

A

This is the temperature (in kelvin) at which the reaction becomes feasible

31
Q

Limitations of using G as an indicator whether a reaction will occur

A

Only indicates if a reaction is feasible
Doesnt take into account rate of the reaction

32
Q

Why is entropy 0 at 0K

A

No disorder
Molecules/atoms are not moving or vibrating and cannot be arranged in any other way
Maximum possible state of order

Chemistry A level (36 decks)

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