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Physical Chemistry > Thermodynamics > Flashcards

Thermodynamics Flashcards

1
Q

What is Hess’ law?

A

energy change is the same irrespective of the route taken

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2
Q

What is standard enthalpy of formation?

A

enthalpy of concentration when one mole of a substance is formed from its elements at 100kPa and all substances are in their standard states

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3
Q

Why does ionic bonding get weaker?

A

as ionic radius increases

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4
Q

Why does Ca2+ have stronger ionic bonding than Na+?

A

greater charge and smaller radius, attracts Cl- more strongly

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5
Q

What is standard enthalpy of atomisation?

A

enthalpy change when one mole of gaseous atoms is formed from their elements at 100kPa in their standard states

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6
Q

What is enthalpy of sublimination?

A

enthalpy change when one mole of solid is converted into one mole of gas

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7
Q

For metals ONLY, what is the relationship between atomisation and sublimination?

A

enthalpy of atomisation = enthalpy of sublimination

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8
Q

What is bond dissociation enthalpy?

A

when one mole of bonds are broken homolytically with all species in the gaseous state

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9
Q

For gaseous diatomic elements like Cl2/F2, what is the relationship between bond dissociation and atomisation, and the exception?

A

enthalpy of bond dissociation = 1/2 enthalpy of atomisation

NOT TRUE FOR Br2 and I2 as they are NOT gaseous at room temp

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10
Q

What is electron affinity?

A

enthalpy change when one mole of electrons is added to one mole of gaseous atoms

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11
Q

The first electron affinity is always…

A

NEGATIVE, EXOTHERMIC due to the attraction of the positive nucleus to the electron being gained

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12
Q

The second electron affinity is always…

A

POSITIVE, ENDOTHERMIC due to the repulsion between the negative ion and the electron being gained

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13
Q

What is the enthalpy of vaporisation?

A

enthalpy change when one mole of a liquid is converted into a gas

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14
Q

Give an example of enthalpy of vaporisation?

A

Br2(l) –> Br2(g)

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15
Q

What is the enthalpy of lattice formation?

A

enthalpy change when one mole of an ionic lattice is formed from gaseous ions

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16
Q

What is the lattice dissociation enthalpy?

A

enthalpy change when one mole of ionic lattice is converted into its gaseous ions

17
Q

The more positive the lattice dissociation enthalpy, the….

A

stronger the ionic bonds

18
Q

The more negative the lattice formation enthalpy….

A

stronger the ionic bonds

19
Q

What is a Born-Haber cycle?

A

a closed loop of enthalpy changes, that include lattice enthalpy

20
Q

When trying to figure out x in a Born-Haber cycle, which direction do you go?

A

tip —>

21
Q

Why are lattice enthalpies of dissociation always endothermic?

A

strong electrostatic bonds between opppositely charged ions are being broken

22
Q

What is the perfect ionic model?

A

-ions are perfectly spherical
-only ionic bonding is present

23
Q

What are two properties of ions that influence the value of a lattice enthalpy using a perfect ionic model?

A

charge and size of ion

24
Q

What is the enthalpy of solution?

A

enthalpy change when one mole of a solid dissolves completely in excess water to form an aqueous solution

25
Q

What is the enthalpy of hydration?

A

enthalpy change when one mole of gaseous ions is converted into aqeuous ions

26
Q

Why are enthalpies of hydration very negative and large?

A

making strong bonds/making strong ion-dipole interactions between ion and polar water molecules

27
Q

How do you calculate the enthalpy of solution?

A

ΔHsol = ΔHlattice dissociation + ΣΔH hydration

28
Q

Why is the theoretical ΔH L.E less than ΔH L.E experimental?

A

-due to _____ having ionic bonding with covalent character

29
Q

Why do silver halides/Ag+/Al3+ have covalent character?

A

the ions are not spherical, there is a higher charge on positive ion and a smaller radius, which polarises/distorts the negative ions more greatly

30
Q

Why is the theoretical ΔH L.E around the same as ΔH L.E experimental for group 1 halides?

A

group 1 halides have ionic bonding only and all ions are spherical

Physical Chemistry (27 decks)

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