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Year 1 Physical Chemistry > Thermodynamics (Topics 1-5) > Flashcards

Thermodynamics (Topics 1-5) Flashcards

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1
Q

K (equilibrium constant) =

A

Concentration of products at equilibrium/concentration of reactants at equilibrium

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2
Q

Molar change in Gibbs free energy (Jmol^-1) =

A

-RTln(K) = Molar Gibbs energy of reactants-products (Jmol^-1)

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3
Q

Fundamental units for heat

A

kg m^2 s^-2 (J)

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4
Q

Boltzmann constant

A

1.381 x 10^-23 J K^-1

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5
Q

Gas constant

A

8.314 J K^-1 mol^-1

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6
Q

Avogadro Constant

A

6.022 x 10^23 mol^-1

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7
Q

Atomic mass unit

A

1.661 x 10^-27 kg

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8
Q

Pascal SI units

A

kg m^-1 s^-2
(N m^-2)

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9
Q

Newton SI units

A

kg m s^-2

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10
Q

Kinetic energy (J)

A

1/2 mass (kg) x velocity^2 (m s^-1)^2

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11
Q

Potential energy (J) =

A

Mass (kg) x gravity (9.81 m s^-2 on earth) x heights (m)

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12
Q

g on earth

A

9.81 m s^-2

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13
Q

Joule in SI units

A

kg m^2 s^-2

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14
Q

Work (J) =

A

Force (N) x distance (m)
-p delta V

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15
Q

Ideal gas law

A

p(Pa) x V(m^3) = n(mol) x R(8.314 J K^-1 mol^-1) x T(K)

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16
Q

Equation linking gas constant and Boltzmann constant

A

R = NA x kB

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17
Q

Real Gas Law

A

(p+an^2 / V^2 )(V-nb) = nRT

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18
Q

Force acting on the piston (N or kg m s^-2) =

A

External pressure (Pa or kg m^-1 s^-2) x Area (m^2)
Area = pi r^2

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19
Q

dw = (2 equations)
Integrated form also

A

-p(ext) pi r^2 (dx) = -p(ext) dV
w = equations above integrated with limits Vf and Vi

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20
Q

Internal energy (J) =

A

Kinetic energy (J) + potential energy (J)

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21
Q

Intensive properties are
Name 3

A

Independent of the size of the system
Temperature
Density
Concentration

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22
Q

Extensive properties are
Name 3

A

A sum of that property for each component subsystem
Entropy
Mass
Volume

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23
Q

Internal energy for monatomic gas = (2 equations)

A

3 kB T / 2 per molecule
3 R T / 2 per mole

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24
Q

Enthalpy change is equal to

A

Heat change

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25
Q

H (J) =

A

U (J) + pV (J)

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26
Q

Change in internal energy (J) =

A

Heat transferred (J) + work done (J)
=0 in an isothermal process
q(rev) (J) + w(rev) (J) = 0

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27
Q

Change in entropy (J K^-1)
4 equations

A

delta S surr = q sys (J) / T (K) = c p,m lnT2 / T1
c integral between Tf and Ti 1/T dT = Cv or Cp ln(Tf/Ti)
-nR {XA ln XA + XB ln XB} where XA / XB = molar fraction of A/B
nR ln (Vf/Vi)

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28
Q

Gibbs Free Energy Change (J)
3 equations

A

Delta G = delta H - T delta S
Delta G = nRT {XA ln XA + XB ln XB} where XA / XB = molar fraction of A/B
Delta G = -nRTlnK

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29
Q

Clausius inequality

A

0 > change in enthalpy - Temperature x change in entropy of system
Change in entropy of system > q / T

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30
Q

For a spontaneous reaction, Gibbs Free Energy Change is

A

Less than 0

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31
Q

State functions
Name 3

A

Depend on the energy of the system
Defines present state and is independent on how that state was reached
Gibbs free energy
Internal energy
Enthalpy
Entropy
(Not heat or work)

32
Q

Gibbs free energy change and enthalpy change calculations
(Involving standards of formation)

A

Gibbs free energy change = sum of (stoichiometrically weighted Gibbs free energy of formation of products - reactants)
Enthalpy change = sum of (stoichiometrically weighted enthalpy change of formation of products - reactants)

33
Q

First Law of Thermodynamics

A

For an isolated system, the change in internal energy is the sum of the heat transferred and the work dome
Delta U = q + w

34
Q

Second Law of Thermodynamics

A

The driving force for a process if entropy
Key to what drives chemical reactions, to predict weather processes will go and what determines the position of equilibrium
The total entropy of an isolated system increases
Delta S > 0

35
Q

Third Law of Thermodynamics

A

The entropy of a system approaches a constant value as the temperature approaches absolute 0
No motion of any type at absolute 0

36
Q

Hess’s Law

A

The total enthalpy change for a reaction is independent of the path by which it occurs

37
Q

Kirchhoff’s Law

A

Integral of dH = integral between T1 and T2 Cp dT
Delta H = H(T2) - H(T1) = Cp(T2 - T1)

38
Q

Pressure exerted by a mixture of gases (Pa) =

A

Sum of the pressure exerted by each gas (partial pressure)

39
Q

Partial pressure (Pa) =

A

Molar fraction x total pressure (Pa)

40
Q

Molar fraction =

A

mol of a gas / total gas moles

41
Q

Total volume (m^3) =

A

nA VA + nB VB
Moles A x vol A + moles B x vol B

42
Q

Gibbs free energy (J) =
2 equations

A

nA GA + nB GB
nA uA + nB uB
u = mu = chemical potential

43
Q

van’t Hoff equation
Integrated form
Indefinite integrated form

A

dlnK/dT = delta H/RT^2
lnK(T2) - lnK(T1) = -delta H/R (1/T2 - 1/T1)
lnK(T) means K at that temp, don’t multiply by temp
lnK = -delta H/R 1/T + delta S/R

44
Q

How would you plot van’t Hoff plot
What does gradient and intercept means

A

Plot: lnK v 1/T
Gradient: -delta H/R
Intercept: delta S/R

45
Q

q(rev) (J) =

A

-w(rev) = nRT ln(Vf/Vi)

46
Q

Heat capacity of a system (c) (JK^-1) =

A

q(rev) (J) / delta T (K)

47
Q

Cv / Cp

A

Heat capacity at constant volume/pressure (J K^-1)

48
Q

d q(rev) =
3 answers

A

Cp dT = TdS = dU + P dV

49
Q

Change in heat capacity at constant pressure (J K^-1)

A

Sum of (stoichiometric weight of products - reactants)

50
Q

dG =
2 lines

A

dH - TdS - SdT
VdP - SdT

51
Q

Rearrange equation dG = VdP - SdT when at constant pressure and temperature

A

-delta S = (d delta G/dT)P
V = (dG/dP)T = nRT/P
P and T outside brackets are subscript

52
Q

Integrated form of V = (dG/dP)T = nRT/P
T subscript

A

Integrated between G1 and G2 dG = nRT integrated between P2 and P1 1/P dP
Delta G = G2-G1 = nRT ln(P2/P1)
PV is constant so can interchange P with V

53
Q

For an exothermic process, the entropy of surroundings … and in an endothermic process, the entropy of surroundings

A

Increases
Decreases

54
Q

1 atmosphere in pascals

A

101325

55
Q

What does the slope gradient represent on the lnk vs 1/T graph

A

-Ea/R

56
Q

Enthalpy is

A

The heat content of a compound at constant pressure

57
Q

Energy can be transferred as

A

Heat or work

58
Q

Maximum work for a system via reversible expansion is achieved by

A

External pressure at maximum
External pressure less than pressure in system
External pressure infinitesimally less than pressure of gas in system

59
Q

Open system

A

Can exchange energy and matter with surroundings

60
Q

Closed system

A

Can exchange energy but not matter with surroundings

61
Q

Isolated system

A

Can’t change energy or matter with surroundings

62
Q

Entropy of the system

A

Measure of randomness
Larger disorder = larger entropy

63
Q

Spontaneous change is driven by

A

The tendency of energy and matter to become disordered.
An increase in entropy in the universe

64
Q

Change in entropy of universe =

A

Change in entropy of surroundings + system

65
Q

Position of equilibrium depends on

A

The relative molar energies of reactants and products

66
Q

Chemical potential

A

Partial molar Gibbs energy

67
Q

When is a system in equilibrium

A

When at constant pressure and temperature the chemical potential of the reactants equals that of the products

68
Q

A real gas will approach ideal gas behaviour under which of the following conditions?

A

High temp
Low pressure

69
Q

In a plot of pressure vs volume for a real gas at the critical temperature, the critical point is

A

a point of inflexion

70
Q

1 m^3 in litres

A

1000

71
Q

A process will be spontaneous if the entropy

A

of the system and surroundings increase

72
Q

2 path functions

A

heat and work
(not state)

73
Q

A positive slope would indicate that the reaction is … in a Van’t Hoff plot

A

exothermic

74
Q

Pressure in irreversible expansion work

A

The value of the external pressure changes
The value of the internal pressure within the
system changes
External pressure must be smaller than the internal pressure within the system

75
Q

Explain how you would determine experimentally the activation energy
(Ea) and pre-exponential factor (A) for a reaction.

A

Measure the rate constant (k) at different temperatures.
Plot lnk versus 1/T
​Determine the slope (m) and y-intercept (c) of the linear fit.
Calculate Ea from the slope:
Ea = −mR.
Calculate A from the intercept: A=e^c

76
Q

delta H =

A

delta U + delta n (g) RT

Year 1 Physical Chemistry (3 decks)

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