DGP Thermodynamics

Question 1

Zeroth Law of Thermodynamics

Answer 1

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.

Question 2

Intensive property

Answer 2

DOES NOT change with the amount of substance. (All molar quantities are intensive).

Question 3

Extensive

Answer 3

DOES change with the amount of substance.

Question 4

Dalton’s Law

Answer 4

In a mixture of ideal gases, the total pressure (p total) is the sum of the partial pressures (p i) of each individual gas.

Question 5

Mole fraction

Answer 5

x = (# of moles of i)/(total # of moles present) = n i / n total

Question 6

When gas expands, it loses _ by doing _

Answer 6

it loses ENERGY by DOING WORK in the surroundings

Question 7

Closed system

Answer 7

Can exchange energy but not matter
(ex = stoppered flask)

Question 8

Open system

Answer 8

Can exchange both energy and matter with its surroundings (ex = open flask)

Question 9

Isolated system

Answer 9

Cannot exchange energy nor matter (ex = sealed flask that is thermally, mechanically, and electrically isolated from its surroundings)

Question 10

Diathermic wall

Answer 10

Permits the passage of energy as heat

Question 11

Adiabatic wall

Answer 11

DOES NOT permit the passage of energy as heat even if there is a temperature difference across the wall

Question 12

Heat

Answer 12

the transfer of energy as a result of a temperature difference between the system and its surroundings

Question 13

Work

Answer 13

the mode of transfer of energy that achieves or utilises uniform motion of atoms in the surroundings

Question 14

w < 0, in gas expansion

Answer 14

When a gas expands by doing work on the surroundings, energy is lost from the system.

Question 15

w > 0, in gas expansion

Answer 15

Work is done onto the system, energy enters the system.

Question 16

When a gas expands against a constant external pressure (such as standard atmospheric pressure, p ex) it is said to do _ work

Answer 16

IRREVERSIBLE work

Question 17

What type of work is the expansion work of an ideal gas?

Answer 17

Mechanical work

Question 18

Mechanical equilibrium

Answer 18

The balance of pressures on either side of a moveable wall

Question 19

A system in mechanical equilibrium does _

Answer 19

MAXIMUM EXPANSION WORK

Question 20

Internal Energy (U)

Answer 20

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).

Question 21

ΔU, change in internal energy

Answer 21

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).

Question 22

FIRST LAW OF THERMODYNAMICS

Answer 22

ΔU = q + w

Question 23

The system LOSES energy when…

Answer 23

• It does work
• It transfers heat to the surroundings

Question 24

The system GAINS energy when…

Answer 24

• Work is done on it ( ex = compression of a gas)
• Heat is transferred to it from the surroundings

Question 25

Enthalpy of vaporisation

Answer 25

Energy that must be supplied as heat at constant pressure to convert 1 mole of a liquid to the gaseous phase.

Question 26

Enthalpy of fusion

Answer 26

Energy that must be supplied as heat at constant pressure to convert 1 mole of a solid to the liquid phase.

Question 27

Enthalpy is a _ function

Answer 27

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.

Question 28

Enthalpy of sublimation, ΔH sub = _ + _

Answer 28

∆𝐬𝐮𝐛𝑯 = ∆𝐟𝐮𝐬𝑯 + ∆𝐯𝐚𝐩𝑯

Question 29

Enthalpy of ionisation, ΔH ion

Answer 29

Molar enthalpy change accompanying the removal of an electron from a gaseous atom or ion.

Question 30

Enthalpy of electron gain, ΔH eg

Answer 30

Molar enthalpy change accompanying the addition of an electron to a gaseous atom or ion.

Question 31

Lattice enthalpy, ΔH lat

Answer 31

Molar enthalpy change when one mole of an ionic lattice is separated to its constituent ions at infinite separation.

Question 32

Hydration enthalpy, ΔH hyd

Answer 32

Molar enthalpy change when one mole gaseous ions become solvated by water molecules in aqueous solution.

Question 33

Standard conditions

Answer 33

Pure, unmixed substances at a pressure of 1 bar with a specified temperature (usually 298K).

Question 34

• Reaction enthalpy, ΔH r
• Standard reaction enthalpy, Δ H r ⦵

Answer 34

• 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

Question 35

Standard enthalpy of combustion, Δ H c ⦵

Answer 35

Change in standard enthalpy per mole of a substance combusting in the presence of excess oxygen.
(substance + oxygen -> carbon dioxide and water).

Question 36

Hess’s Law

Answer 36

The standard enthalpy of a reaction is the sum of the standard enthalpies of the reactions into which the overall reaction may be divided.

Question 37

Standard enthalpy of formation, Δ H f ⦵

Answer 37

The standard enthalpy (per mole of the substance) for its formation from its elements in their reference states.

Question 38

Reference state

Answer 38

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.

Question 39

Δ H f ⦵ for an element in its reference state is _

Answer 39

ZERO

Question 40

Δ H r ⦵ = ?

Answer 40

Δ H r ⦵ = Δ H f ⦵ (products) - Δ H f ⦵ (reactants)

∆𝒓𝑯⦵= ∑𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠 𝒏𝒊 × ∆𝒇𝑯⦵(products) − ∑𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡𝑠 𝒏𝒊 × ∆𝒇𝑯⦵(reactants)

Question 41

ΔS total = _ + _

Answer 41

ΔS total = ΔS system + ΔS surroundings

Question 42

Trouton’s Rule

Answer 42

• 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.

Question 43

SECOND LAW OF THERMODYNAMICS

Answer 43

For a spontaneous process, the entropy of the universe increases.

Question 44

THIRD LAW OF THERMODYNAMICS

Answer 44

The entropy of a perfect crystal is zero at zero kelvin.

Question 45

Δ S ⦵ = ?

Answer 45

Δ S r ⦵ = Δ S ⦵ (products) - Δ S ⦵ (reactants)

∆𝒓S⦵= ∑𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠 𝒏𝒊 × ∆S⦵(products) − ∑𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡𝑠 𝒏𝒊 × ∆S⦵(reactants)