DGP Thermodynamics Flashcards
Zeroth Law of Thermodynamics
If System A is in thermal equilibrium with System B, and System B is in thermal equilibrium with System C, then System A is in thermal equilibrium with System C.
Intensive property
DOES NOT change with the amount of substance. (All molar quantities are intensive).
Extensive
DOES change with the amount of substance.
Dalton’s Law
In a mixture of ideal gases, the total pressure (p total) is the sum of the partial pressures (p i) of each individual gas.
Mole fraction
x = (# of moles of i)/(total # of moles present) = n i / n total
When gas expands, it loses _ by doing _
it loses ENERGY by DOING WORK in the surroundings
Closed system
Can exchange energy but not matter
(ex = stoppered flask)
Open system
Can exchange both energy and matter with its surroundings (ex = open flask)
Isolated system
Cannot exchange energy nor matter (ex = sealed flask that is thermally, mechanically, and electrically isolated from its surroundings)
Diathermic wall
Permits the passage of energy as heat
Adiabatic wall
DOES NOT permit the passage of energy as heat even if there is a temperature difference across the wall
Heat
the transfer of energy as a result of a temperature difference between the system and its surroundings
Work
the mode of transfer of energy that achieves or utilises uniform motion of atoms in the surroundings
w < 0, in gas expansion
When a gas expands by doing work on the surroundings, energy is lost from the system.
w > 0, in gas expansion
Work is done onto the system, energy enters the system.
When a gas expands against a constant external pressure (such as standard atmospheric pressure, p ex) it is said to do _ work
IRREVERSIBLE work
What type of work is the expansion work of an ideal gas?
Mechanical work
Mechanical equilibrium
The balance of pressures on either side of a moveable wall
A system in mechanical equilibrium does _
MAXIMUM EXPANSION WORK
Internal Energy (U)
The sum of all the kinetic and potential contributions to the energy of all the atoms, ions, and molecules in the system. U is an extensive property unless reported as molar internal energy: Um = U/n (units: J per mole).
ΔU, change in internal energy
ΔU = q + w
Where q is the energy transferred to the system as heat (if energy is LOST by the system as heat this quantity is negative).
Where w is the energy transferred to the system as work (if work is DONE BY the system onto the surroundings, energy is lost and this quantity is negative).
FIRST LAW OF THERMODYNAMICS
ΔU = q + w
The system LOSES energy when…
- It does work
- It transfers heat to the surroundings
The system GAINS energy when…
- Work is done on it ( ex = compression of a gas)
- Heat is transferred to it from the surroundings
Enthalpy of vaporisation
Energy that must be supplied as heat at constant pressure to convert 1 mole of a liquid to the gaseous phase.
Enthalpy of fusion
Energy that must be supplied as heat at constant pressure to convert 1 mole of a solid to the liquid phase.
Enthalpy is a _ function
STATE function
The fact that enthalpy is a state function implies that, under the same conditions of temperature and pressure, the enthalpy change of a reverse process is the negative of the enthalpy change of the forward process.
Enthalpy of sublimation, ΔH sub = _ + _
∆𝐬𝐮𝐛𝑯 = ∆𝐟𝐮𝐬𝑯 + ∆𝐯𝐚𝐩𝑯
Enthalpy of ionisation, ΔH ion
Molar enthalpy change accompanying the removal of an electron from a gaseous atom or ion.
Enthalpy of electron gain, ΔH eg
Molar enthalpy change accompanying the addition of an electron to a gaseous atom or ion.
Lattice enthalpy, ΔH lat
Molar enthalpy change when one mole of an ionic lattice is separated to its constituent ions at infinite separation.
Hydration enthalpy, ΔH hyd
Molar enthalpy change when one mole gaseous ions become solvated by water molecules in aqueous solution.
Standard conditions
Pure, unmixed substances at a pressure of 1 bar with a specified temperature (usually 298K).
- Reaction enthalpy, ΔH r
- Standard reaction enthalpy, Δ H r ⦵
- Change in enthalpy accompanying a chemical reaction
- Change in enthalpy accompanying a chemical reaction proceeding from pure unmixed reactants, to pure and unmixed products, under standard conditions
Standard enthalpy of combustion, Δ H c ⦵
Change in standard enthalpy per mole of a substance combusting in the presence of excess oxygen.
(substance + oxygen -> carbon dioxide and water).
Hess’s Law
The standard enthalpy of a reaction is the sum of the standard enthalpies of the reactions into which the overall reaction may be divided.
Standard enthalpy of formation, Δ H f ⦵
The standard enthalpy (per mole of the substance) for its formation from its elements in their reference states.
Reference state
Substances’ most stable form under prevailing conditions (usually 298.15 K and 1 bar).
DO NOT confuse ‘reference state’ with ‘standard state’. Standard state is any specified state of the element at 1 bar.
Δ H f ⦵ for an element in its reference state is _
ZERO
Δ H r ⦵ = ?
Δ H r ⦵ = Δ H f ⦵ (products) - Δ H f ⦵ (reactants)
∆𝒓𝑯⦵= ∑𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠 𝒏𝒊 × ∆𝒇𝑯⦵(products) − ∑𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡𝑠 𝒏𝒊 × ∆𝒇𝑯⦵(reactants)
ΔS total = _ + _
ΔS total = ΔS system + ΔS surroundings
Trouton’s Rule
- When a liquid vaporises, the compact condensed liquid phase transforms into a gas that is highly random and disordered no matter what substance is involved (entropy increases).
- (To a good approximation) The change in entropy accompanying vaporisation is the same for all liquids at their boiling temperatures: +85 J K^-1 mol^-1
This allows a useful means of estimated the enthalpy of vaporisation if T vap is known.
SECOND LAW OF THERMODYNAMICS
For a spontaneous process, the entropy of the universe increases.
THIRD LAW OF THERMODYNAMICS
The entropy of a perfect crystal is zero at zero kelvin.
Δ S ⦵ = ?
Δ S r ⦵ = Δ S ⦵ (products) - Δ S ⦵ (reactants)
∆𝒓S⦵= ∑𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠 𝒏𝒊 × ∆S⦵(products) − ∑𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡𝑠 𝒏𝒊 × ∆S⦵(reactants)
