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A Level Physical Chemistry > Section 6 - Thermodynamics > Flashcards

Section 6 - Thermodynamics Flashcards

1
Q

Define enthalpy change

A

The heat energy transferred in a reaction at constant pressure

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2
Q

What are standard conditions for enthalpy change?

A

298K and 100kPa

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3
Q

What type of reaction has a positive enthalpy change?

A

Endothermic

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4
Q

What type of reaction has a negative enthalpy change?

A

Exothermic

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5
Q

Define enthalpy change of formation

A

The enthalpy change when 1 mole of a compound is formed from its elements in their standard states under standard cpmdotopms

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6
Q

Define bond dissociation enthalpy

A

The enthalpy change when all the bonds of the same type in 1 mole of gaseous molecules are broken

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7
Q

Define enthalpy change of atomisation of an element

A

The enthalpy change when 1 mole of gaseous artoms is formed from an element in its standard state.

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8
Q

Define enthalpy change of atomisation of a compound

A

The enthalpy change when 1 mole of a compound in its standard state is converted to gaseous atoms

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9
Q

Define first ionisation energy

A

The enthalpy change when 1 mole of gaseous 1+ ions is formed from 1 mole of gaseous atoms

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10
Q

Define second ionisation energy

A

Enthalpy change when 1 mole of gaseous 2+ ions is formed from 1 mole of gaseous 1+ ions

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11
Q

Define first electron affinity

A

Enthalpy change when 1 mole of gaseous 1- ions is formed from 1 mole of gaseous atoms

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12
Q

Define second electron affinity

A

Enthalpy change when 1 mole of gaseous 2- ions is formed from 1 mole of gaseous 1- ions

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13
Q

Define enthalpy change of hydration

A

Enthalpy change when 1 mole of aqueous ions is formed from 1 mole of gaseous ions

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14
Q

Define enthalpy change of solution

A

Enthalpy change when 1 mole of solute is dissolved in enough solvent that no furhter enthalpy change occurs on further dilution

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15
Q

Define lattice enthalpy of formation

A

Enthalpy change when 1 mole of solid ionic compound is formed from its gaseous ions under standard conditions

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16
Q

Define lattice enthalpy of dissociation

A

Enthalpy change when 1 mole of a solid ionic compound is completely dissociated into its gaseous ions under standard conditions

17
Q

What is Hess’ Law?

A

Enthalpy change is independent of route taken

18
Q

Why are theoretical lattice enthalpies different from experimental values?

A

Theoretical lattice enthalpies are based on the assumption that all ions are spherical and have their charges evenly distributed.

Usually slight polarisation occurs between neighbouring positive and negative ions so most ionic compounds have some covalent character and aren’t exactly spherical.

19
Q

Why does dissolving have an enthalpy change?

A

The bonds between ions break which is endothermic

Bonds form between the ions and water which is exothermic

The enthalpy change of solution is the overall effect of these

20
Q

Why can water molecules bond to ions?

A

Oxygen is more electronegative than hydrogen so water is polar. The H can bond to the negative ions and the O can bond to the positive ions.

21
Q

Why do soluble substances tend to have exothermic enthalpies of solution?

A

Substanes tend to only dissolve if the energy released is roughly the same as or greater than the energy taken in.

22
Q

What is entropy?

A

A measure of the number of ways that particles can be arranged and the number of ways that the energy can be shared out between particles.

23
Q

What factors affect entropy?

A
  • physical state
  • amount of particles
24
Q

Do stable substances have more or less disorder?

A

More

25
Q

What is the formula for entropy change of a reaction?

A

Sproducts - Sreactants

26
Q

Define standard entropy of a substance

A

The entropy of 1 mole of that substance under standard conditions

27
Q

For a reaction to be feasible, what must ΔG be?

A

Negative or 0

28
Q

What is the formula for Free Energy Change?

A

ΔG = ΔH - TΔS

29
Q

How do you find the temperature at which a reaction is feasible?

A

Use T=ΔH/ΔS to find when ΔG = 0

A Level Physical Chemistry (9 decks)

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