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Core Chemistry 2 > Thermodynamics 2 > Flashcards

Thermodynamics 2 Flashcards

1
Q

Laws of thermodynamics: Zeroth law

A

if two systems have different temperatures, they exchange heat, q, until they are in thermal equilibrium

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2
Q

Laws of thermodynamics: First law

A

internal energy, U, is the sum of a system’s potential and kinetic energies

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3
Q

Laws of thermodynamics: Second law

A

entropy of an isolated system increases in a spontaneous process: ΔS>0

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4
Q

Entropy, S

A

a measure of the dispersal of energy

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5
Q

Laws of thermodynamics: Third law

A

the entropy of all perfect crystalline substances is 0 at T = 0K

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6
Q

When is enthalpy H a more useful measure than internal energy U?

A

at constant pressure because change in enthalpy is just the flow of heat

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7
Q

dH < 0

A

process is exothermic

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8
Q

dH > 0

A

process is endothermic

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9
Q

Isolated system

A

no exchange of energy or matter with the surroundings

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10
Q

Closed system

A

exchange of energy with the surroundings but not matter

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11
Q

Open system

A

exchange of energy and matter with the surroundings

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12
Q

Equal pressure

A

mechanical equilibrium

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13
Q

Equal temperature

A

(heat flows to give…) thermal equilibrium

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14
Q

Equal number of molecules, N i

A

( species i diffuse, phase transform or react to give…) chemical equilibrium of species i

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15
Q

What can chemical potential of i be thought as in a mixture?

A

the change in free energy of a VERY large system when you add one mole of component i

(has to be a very large system so when one mole is added, it doesn’t affect the system)

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16
Q

How does chemical potential relate with vapour pressure?

A

Chemical potential decreases if vapour pressure decreases

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17
Q

A perfect (or ideal) gas

A

gas with no interactions between its molecules

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18
Q

An ideal solution or ideal liquid mixture

A

has identical interactions between its molecules, irrespective of the molecules’ identity

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19
Q

A non-ideal solution or non-ideal liquid mixture

A

has different interactions between like and unlike molecules

20
Q

Why does chemical potential decrease when vapour pressure and mole fraction decreases?

A

due to the increase in molar entropy arising from the increased accessible volume (a larger accessible volume means a greater dispersion of energy)

21
Q

Criteria for equilibrium

A

chemical potential is the same in all phases present

22
Q

What is the Clapeyron Equation used for?

A
  1. To find gradient of p-T boundary lines -> gives sign of Δ tr V
  2. Estimate Δ tr H or the effect of pressure on mp’s
23
Q

What is the Clausius-Clapeyron Equation used for?

A
  1. To estimate vapour pressires, T b , or T sub
  2. To find Δ tr H via plotting ln p vs 1/T
24
Q

Perfect (or ideal) gas

A

NO interactions between its molecules

25
Q

Ideal solution or ideal liquid mixture

A

IDENTICAL interactions between its molecules, irrespective of the molecules’ identity

26
Q

Non-ideal solution/ liquid mixture

A

DIFFERENT interactions between like and unlike molecules

27
Q

Raoult’s Law

A
  • Solutions and liquid mixtures obeying Raoult’s law are known as ideal
  • Raoult’s law holds increasingly well as x A → 0
28
Q

Why does chemical potential decrease as the partial pressure of A and the mole fraction of A decrease?

A

due to the increase in molar entropy arising from the increased accessible volume (a larger accessible volume means a greater dispersion of energy)

29
Q

Chemical potential of a species

A

the energy that can be absorbed or released due to a change of the particle number of the given species

30
Q

Effect of adding solute into solvent regarding T m and T b

A
  • Adding solute lowers the melting point and raises the boiling point because the entropy of solution state is higher than the pure liquid
  • Change in boiling point is SMALLER than change in melting point
31
Q

What do the changes in melting and boiling points depend upon?

A
  • the mole fraction of the solute, not its identity
  • the number of particles so for molecules that dissociate (e.g. salts) it is the total number of particles that matter
32
Q

What is a colligative property important for biology?

A

Osmotic pressure

33
Q

Osmotic pressure defined

A

the pressure that when applied to a solution, prevents the influx of solvent through a semipermeable membrane

34
Q

Colligative properties

A

solution properties that depend only on the number of solute particles present and not their identity. They arise because the presence of a solute (B) reduces the chemical potential of the solvent (A)

35
Q

Osmometry

A

a sensitive way of determining molar masses of macromolecules using dilute solutions

36
Q

What can reverse osmosis be used for?

A

purifying sea water

37
Q

Effects of solutes being added to solvent

A

Raises the boiling point and depresses the melting point of a solvent. For dilute solutions, the change in b.p. or m.p. is proportional to the mole fraction of solute. Solutes lower the melting point more than they raise the boiling point.

38
Q

What is the eutectic point (e)?

A

it is the minimum melting point of the mixture

39
Q

What is the composition at e known as and what does it mean?

A

the eutectic composition - mixtures with the eutectic composition melt and freeze without changing their composition

40
Q

What happens at the eutectic point in binary mixtures?

A

the liquid mixture is in equilibrium with solid A and solid B

41
Q

What sort of systems give lower eutectic points?

A

Non-ideal systems with A-B interactions more favourable than A-A and B-B ones

42
Q

What is the liquid-vapour coexistence line?

A

where the liquid mixture is in equilibrium with the vapours A and B at total pressure p

43
Q

What is y A ?

A

the mol fraction of A in the gas phase

44
Q

Phase diagrams for ideal binary mixtures: how does vapour pressure link to boiling point?

A

a higher vapour pressure corresponds to a lower boiling point, so a T-z phase diagram looks roughly like an inverted p-z phase diagram

45
Q

What are phase diagrams useful for discussing?

A

fractional distillation

46
Q

Why does the Gibbs phase rule arise?

A

directly from the requirement of the chemical potential to be the same in all phases that are in equilibrium

47
Q

What do tie-lines (horizontal lines in two-phase region) do on phase diagrams?

A

they connect two phases in equilibrium (i.e. with the same chemical potentials)

Core Chemistry 2 (4 decks)

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