Physical chemistry (Horrocks)

Question 1

Define isolated system

Answer 1

exchange neither energy nor matter

Question 2

Define closed system

Answer 2

exchange energy, but not matter

Question 3

Define open system

Answer 3

exchange energy and matter

Question 4

What is the ideal gas equation and there units

Answer 4

pV = nRT
pressure / N m−2 or Pa
volume / m3
R = 8.314 J K−1 mol−1
n = mol

Question 5

What is van der Waals gas law and what do the letters stand for.

Answer 5

p = (nRT/(V-nb))-a*(n/V)^2
a accounts for attractive interactions between the molecules
b accounts for repulsive interactions (finite size effect)

Question 6

Advantages and disadvantages of ideal gas equation

Answer 6

Applies approximately to all gases at near-ambient temperatures and
pressures
No molecule-specific parameters; n is the total number of moles of
gas even if the gas is a mixture.
Fails to predict that gases liquefy at low temperature and high
pressure

Question 7

Advantages and disadvantages of van der Waals gas law

Answer 7

Accounts for liquefaction (partially)
More accurate than the ideal gas law
Requires a knowledge of the a and b parameters for all the gas
species involved – the main reason we do not use it as much as the
ideal gas law.

Question 8

What is the equation for compression or expansion of a gas

Answer 8

w = −p (Vf − Vi) = −p∆V

Question 9

What are some key points about the equation for compression or expansion of a gas

Answer 9

work done on the gas is positive when the gas is compressed.
work done by the gas is negative when the gas is compressed.
work done on the gas = - work done by the gas
w / Joules (J)
∆V < 0 for compression; ∆V > 0 for expansion.

Question 10

define heat

Answer 10

Heat is the transfer of energy in a disorganised form, driven by a
difference of temperature.

Question 11

define work

Answer 11

Work is the transfer of energy in an organised form.

Question 12

what do the following letters mean U, H, CV ,m, Cp,m

Answer 12

u = total energy
H = enthalpy
CV,m = heat capacity at constant volume
CP,m = heat capacity at constant pressure

Question 13

what is the equation for enthalpy

Answer 13

total energy + (pressure*volume)

Question 14

define molar heat capacity

Answer 14

The heat required to raise the temperature of one mole of substance by
one Kelvin.

Question 15

what is the total energy change for an isolated system

Answer 15

0

Question 16

what is the total energy change for a closed system

Answer 16

q + w
heat + work

Question 17

define system

Answer 17

the portion of the universe under study

Question 18

define surroundings

Answer 18

everything not part of the system

Question 19

define thermodynamic variable

Answer 19

Quantities that pertain to the bulk properties of matter and which can, in principle, be
controlled in an experiment

Question 20

define thermodynamic state

Answer 20

A specification of the values of the thermodynamic variables that uniquely define the condition and thermodynamic properties of a system

Question 21

define equation of state

Answer 21

equation relating the values of the thermodynamic variables

Question 22

define state function

Answer 22

A quantity that depends only on the thermodynamic state of a system and not on how it was prepared.

Question 23

define entropy

Answer 23

a measure of disorder, both of energy and matter

Question 24

give the 4 definitions of reversible process

Answer 24

• A process for which the system and surroundings can both be returned to their
  initial conditions.
• A process for which the total change in entropy of system and surroundings together
  is zero.
• A process which proceeds through a succession of equilibrium states.
• A process for which (∆G)p,T = 0.

Question 25

define standard state/ conditions

Answer 25

* the most stable form of that substrate at a pressure of one bar * Temperature is not part of the of the definition, standard state may be any temperature

Question 26

define reference state

Answer 26

the stable form of the element under standard condition

Question 27

define standard formation reaction

Answer 27

A reaction in which one mole of the substance is prepared under standard conditions from the elements in their reference states. The changes in two important state functions H, G for these reactions are tabulated as ∆f H⊖ and ∆f G⊖.

Question 28

define mean bond enthalpy

Answer 28

The ∆H for a reaction X − Y → X + Y averaged over a large selection of compounds with X − Y bonds is the mean bond enthalpy for X − Y bonds

Question 29

define enthalpy of combustion

Answer 29

Enthalpy change when 1 mole of substance is combusted to liquid water and gaseous CO2 and N2 (if any N-atoms) under standard conditions. Symbol: ∆comH⊖

Question 30

define activity

Answer 30

A dimensionless (no units) quantity related to concentration or pressure that is used to express the equilibrium constant. The activity of species A may be denoted {A} or aA for pure solids or liquids the activity is 1

Question 31

define gibbs energy

Answer 31

Gibbs energy, also called free energy, G, is defined as: G = H − T S or equivalently G = U + pV − T S

Question 32

define useful work

Answer 32

Work done that corresponds to expansion of the system against an external pressure is called pV -work or expansion work. All other types of work are called ’useful’ work.

Question 33

define equilibrium constant

Answer 33

A ratio of activities of products and reactants, raised to the powers of the stoichiometric coefficients in the balanced chemical equation. The equilibrium constant for a particular choice of reaction depends only on the temperature

Question 34

define intensive variable

Answer 34

A thermodynamic variable that does not scale with the size of the system

Question 35

define extensive variable

Answer 35

A thermodynamic variable that does scale with the size of the system

Question 36

define degrees of freedom

Answer 36

A degree of freedom is an intensive variable whose value can be chosen by the experimenter. p, T , mole fractions xi.

Question 37

define phases

Answer 37

a phase is a uniform state of matter

Question 38

define components

Answer 38

A component is an independent chemical species in the system, whose quantity can be chosen by the experimenter. The number of components is the number of species minus the number of equilibria amongst them and minus the number of electroneutrality constraints.

Question 39

define mole fraction

Answer 39

The fraction of a species in a mixture calculated on the basis of numbers of moles of each species.

Question 40

define phase rule

Answer 40

F = C - P+2

Question 41

define normal melting point

Answer 41

The temperature at which the solid and liquid phases are in equilibrium at a pressure of 1 atm.

Question 42

define normal boiling point

Answer 42

The temperature at which the liquid and gaseous phases are in equilibrium at a pressure of 1 atm

Question 43

define critical point

Answer 43

The highest temperature at which the liquid phase exists. The ’end’ of the liquid-gas boundary line on the phase diagram

Question 44

define triple point

Answer 44

The unique temperature and pressure at which the solid, liquid and gaseous phases of a pure substance are in equilibrium

Question 45

define half cell reaction

Answer 45

The reaction occurring at a single electrode in which electrons are transferred to/from solution

Question 46

define cell rection

Answer 46

The overall reaction taking place in the cell. Conventionally the difference between the right and left half cell reactions

Question 47

define faraday's law

Answer 47

Relationship between number of moles of an electrode reaction and the electrical charge passed. * Q = nF * Charge, Q in Coulombs, C. Number of moles, n and the Faraday constant F = 96485 C mol−1

Question 48

define the standard hydrogen electrode

Answer 48

The conventional zero for the electrode potential scale. * The electrode reaction for the SHE is: H+ + e− = 1/2H2 * When all species are in their standard states E (SHE) = 0 V. * It is implemented by dipping an inert Pt electrode in 1M HCl and bubbling H2 through the solution at 1 bar

Question 49

define cell potential

Answer 49

The potential difference between the two electrodes (half cells) of a cell. E = ER − EL

Question 50

define electrode potential

Answer 50

the cell potential for a cell in which the left hand electrode is the she

Question 51

what is the acid dissociation constant

Answer 51

The equilibrium constant for the dissociation equilibrium of a weak acid. HA = H+ + A− * Usual symbol Ka * Usually reported as a p-value: pKa = − log10 Ka

Question 52

what is the base dissociation constant

Answer 52

The equilibrium constant for the dissociation equilibrium of a weak base. B + H2O ⇀ BH+ + OH− * Usual symbol Kb * Usually reported as a p-value: pKa = − log10 Kb

Question 53

define pH

Answer 53

pH = − log10{H+} {H+} is the hydrogen ion activity

Question 54

what is the ionic product of water

Answer 54

The equilibrium constant for the autoionization (acid dissociation) reaction of water. H2O ⇀↽ H+ + OH− * Usual symbol KW * At 298 K KW ≃ 10−14 * pKa + pKb = pKW = 14

Question 55

define solubility product

Answer 55

The equilibrium constant for the dissolution of a salt. * Usual symbol Ksp

Question 56

define azeotrope

Answer 56

A mixture of two or more liquids which has a constant boiling point and composition throughout distillation. In particular, the vapour has the same composition as the liquid

Question 57

define fractional distillation

Answer 57

Separation of a mixture by repeated evaporation-condensation-evaporation

Question 58

define eutectic

Answer 58

A homogeneous mixture of solids that melts at a temperature that is lower than any of its components. The eutectic mixture melts and freezes as if it were a pure compound rather than a mixture - it does not separate into different components upon melting/freezing. * The eutectic temperature (aka eutectic point) is the lowest possible melting tem- perature amongst all of the mixing ratios for the components involved

Question 59

define colligative properties

Answer 59

A property of a solution/mixture that depends on the mole fraction of solute species and not on their chemical identity

Question 60

define osmotic property

Answer 60

The difference in pressure between a solvent and a solution that are separated by a semi- permeable membrane that only allows solvent molecules to cross

Question 61

what is Dalton's law

Answer 61

The partial pressure of a gas in a mixture is the mole fraction times the total pressure. pA = xAp * Each gas contributes a partial pressure to the overall pressure that is proportional to its mole fraction. * Dalton’s law is accurate in so far as the gases are ideal

Question 62

what is Raoult's law

Answer 62

The partial vapour pressure of a solvent in a mixture is proportional to its mole fraction in the solution and its vapour pressure when pure. pA = xAp∗ * p∗ is the vapour pressure of pure solvent. * Solutions that obey Raoult’s law are called ideal solutions

Question 63

what is Henry's law

Answer 63

The partial vapour pressure of a solute in a solution is proportional to its mole fraction. pB = xB KB * KB is NOT the vapour pressure of pure solvent unless the solution is ideal for all mole fractions. * Solutions that obey Henry’s law are called ideal-dilute solutions

Question 64

define entropy of mixing

Answer 64

The change in entropy that occurs when two or more components are mixed in an ideal mixture (or solution). ∆mixS = −nR (xA ln xA + xB ln xB + xC ln xC ...) * The entropy of mixing is always positive. * The formula above is accurate in so far as the mixture is ideal

Question 65

define tie line

Answer 65

A horizontal line on the temperature-mole fraction diagram for a mixture. The ends of the tie line indicate the compositions of the liquid and vapour phases (or solid and liquid phases). The amounts of liquid and vapour are given by the lever rule.

Question 66

what is the 0th law of thermodyamics

Answer 66

if 2 systems are in equilibrium with a 3rd system then they are in equilibrium with each other

Question 67

what is the 1st law of thermodynamics

Answer 67

Δ U =0 for an isolated system and Δsys U + Δsurr U =0 for open/closed systems Meaning conservation of energy. If a system is not isolated, then energy lost by the system is gained by the surroundings, i.e., is transferred from system to surroundings

Question 68

what is the second law of thermodynamics

Answer 68

Δ S≥0 for an isolated system and Δ Ssys+ ΔSsurr ≥0 for open/closed systems Meaning in an isolated system, entropy increases until equilibrium is reached when it stays constant; entropy does not decrease in an isolated system. If a system is not isolated, then entropy lost by the system must be at least balanced by that gained by the surroundings; the total entropy of system + surroundings never decreases.

Question 69

what is the 3rd law of thermodynamics

Answer 69

S=0 at 0 K or a perfect crystal. . The entropy of a perfect crystalline substance is zero at absolute zero.

Question 70

What is troutons rule

Answer 70

states that the (molar) entropy of vaporization is almost the same value, about 85–88 J/(K·mol), for various kinds of liquids at their boiling points.

Question 71

What is Kirchhoffs law

Answer 71

At constant pressure, the heat capacity is equal to change in enthalpy divided by the change in temperature

Question 72

What is coulombs law

Answer 72

the force of attraction or repulsion between two charged bodies is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.