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Chemistry 2 > Chemistry Y6: Thermodynamics > Flashcards

Chemistry Y6: Thermodynamics Flashcards

1
Q

What is the 1st law of thermodynamics?

A

Energy can be converted from one form to another but the total amount of e energy in the universe is constant.

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2
Q

What is the two types of energy stores for substances?

A

Kinetic and potential energy

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3
Q

What can change the internal energy (U) of a system?

A

1) Transfer of heat (to and from surroundings)
2) Work being done (on or by the system)

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4
Q

What is another way of saying U = U(system) FINAL -U(system) INITIAL?

A

U = KE + KP

  • Kinetic and potential energy
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5
Q

What is the equation for C (SHC) at constant volume (V)?

A

Cv = ( d̂U/d̂T)V = dQ/dT

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6
Q

At constant pressure what does dH equal?

A

dH=dQ
= to the amount of heat transferred between the systems and the surrounding during a process

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7
Q

what is the 2nd law of thermodynamics?

A

1) heat never flows spontaneously from cold body to a hot body
2) Any spontaneous change must be accompanied by an increase in entropy of the universe

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8
Q

What is the mathematical definition of entropy?

A

ds = dQ/T
Jk-1mol-1

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9
Q

Which is bigger Latent heat of fusion or the Latent heat of vaporisation?

A

Vaporisation

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10
Q

What are the stationary parts on a graph of entropy vs Temperature?

A

Melting and Boiling
* stationary as energy is being used to change state

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11
Q

What is the calculation of change in Entropy (ΔS) from T2 to T1?

A

ΔS = C ln (T2/T1)

T = temperature (k)

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12
Q

What is the definition of statistical entropy / Equation for S across changing states?

A

S = Kb ln(W)

Kb = Boltzmann constant
W = number of states

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13
Q

What is the 3rd law of thermodynamics?

A

S= Kb ln(W)

For a perfect crystal at 0K, since there is only 1 possible configuration (W=1), S =0

As S= Kb ln(1) = 0

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14
Q

What is the calculation of change in Entropy (ΔS) from V2 to V1?

A

ΔS= nRln (V2/V1)

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15
Q

Does a system favour having a high or low entropy

A

High entropy

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16
Q

The feasibility of a reaction based on the difference between the Reactants and products is known as

A

Gibbs free energy , G

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17
Q

What is the equation for Gibbs free energy at constant temp and pressure?

A

ΔG = ΔH-TΔS

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18
Q

what are the limitations of Gibbs?

A
  1. If pressure isn’t constant
  2. if we think of internal energy in Helmholts energy, F
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19
Q

What is the equation for Helmholtz energy?
-When will a reaction be spontaneous?

A

F= U-TS

when 𝝙F < 0
-Same as 𝝙G

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20
Q

What if pressure isn’t constant when calculating Gibbs

A

You have to calculate in terms of U, internal energy, rather than using enthalpy.

This used Helmholtz energy, F

F = U - TS

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21
Q

What is the gibs equation when we vary temperature and pressure

A

dG= VdP - SdT

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22
Q

How do we take partial derivatives of G where Pressure is constant?

A

(d̂G/d̂T)P = -S

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23
Q

How do we take partial derivatives of G where temperature is constant?

A

(d̂G/d̂P)T = V

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24
Q

If temperature increases, what happens to S and G

A

S always increases
G always decreases

dG=-SdT

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25
Q

Does G vary more with a smaller or larger volume?

A

A larger volume

dG=VdP

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26
Q

As pressure increases what happens to G

A

Since molecular volume is getting smaller, the effect on G is getting Smaller.

dG= VdP

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27
Q

What is sublimation?

A

(s) -> (g)

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28
Q

At constant temp what does dG equal?

A

dG = VdP

V always +ve so, G always increases with pressure

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29
Q

What is the ideal gas equation?

A

PV=nRT

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30
Q

What is the ideal gas equation for 1 mol of gas

A

V=RT/P

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31
Q

What is the equation linking ideal gas to ΔG

A

ΔG= RT ln(P2/P1)
Units Kj.mol-1

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32
Q

What is 𝝙G⁰, and what is its equation?

A

it is the different in Gibbs energies of R’s and P’s when they’re in their standard states

𝝙G⁰= sum G⁰ Products - sum G⁰ Reactants

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33
Q

What are the standard states?

A

Temp = 298K
Pressure = 1atm
Concentration = 1 mol.L-1

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34
Q

What is the most stable phase of a material

A

Which ever has the lowest Gibbs energy

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35
Q

What is the equation we use when reactants and products are not in standard states to get change in Gibbs (ΔG)

A

ΔG = ΔG⁰ + RTlnQ

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36
Q

When Q= K what does ΔG equal?
Turn this into an equation

A

ΔG = 0
0=ΔG⁰ + RTlnK

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37
Q

If, 0=ΔG⁰ + RTlnK
What does ΔG⁰ equal?

A

ΔG⁰ = -RTlnK

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38
Q

What is the quadratic formula and when do you. need to use it?

A

In K ( rate) calculations
____________
X= -b+/- _/ (b²-4ac/2a)

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39
Q

what is the equation for Ui (chemical potential) ?

A

Ui = (d̂G/d̂ni)PTn

40
Q

what is total Gibbs free energy of a binary mixture?

A

G= nAUB + nBUB
n= no. moles
U= chemical potential

41
Q

what does U depend on?

A

Temperature / pressure
-so G can vary with n/u

42
Q

combine G= nAUB + nBUB
and dG = VdP- SDT

A

dG = VdP -SdP + UAdnA + UBdnB

43
Q

write an equation of dG and its relationship with T/P

A

dG = VdP- SDT

44
Q

What is ΔG reaction?

A

It is the difference in chemical potentials at the composition of the mixture
-G of a reaction system tries to minimise itself
-Reaches 𝝙G at equilibrium (lowest point on graph)

45
Q

Variation of 𝝙G with composition- show how chemical potential of component i varies
-What does this tell is

A

Ui = Ui ⁰ + RT lnai

ai = activity of i

Direction a reaction will move

46
Q

What is Le Chatalier’s principle

A

When a system at equilibrium is changed, the system will adjust to decrease the effect of that change

47
Q

Say 𝝙H is negative, what happens when you increase/decrease temperature?

A

℃ Increase = R’s lose heat, exo favoured= forward reaction, K increases

℃ Decrease = R’s gain heat, endo favoured = backwards reaction, K decreases

48
Q

if 𝝙S is +ve, how does ΔG⁰ change with temp?
if 𝝙S is -ve, how does ΔG⁰ change with temp?

A
  1. Increased temp = Increased G
  2. Increased temp = decreased G
49
Q

What states are relevant in entropy

A

only (g)

50
Q

What is the chemical potential of a substance in a mixture?

A

It is the contribution of that substance to the total Gibbs energy of the mixture

51
Q

What is the Vant Hoff equation and what does it tell us

A

LnK2-Lnk1= ΔH⁰/R [1/T1 - 1/T2]
Tell us how K changes as temperature changes

52
Q

what is vapour pressure?

A

the pressure exerted by a vapour
-Related to the (s)/(l) evaporation rate
-More volatile a substance = greater VP
-increased temp = increase KE= greater VP

53
Q

What is the Clausius- Clapeyron equation and what does it tell us?

A

LnP2 - LnP1 = ΔH vap/R [1/T1 - 1/T2]
It tells us how P changes as temperature changes

54
Q

What is the effect of altitude on bp?

A

atm pressure decreases at higher altitudes
-So water boils at lowere temperatures

55
Q

When does SVP = ATM pressure of surroundings

A

boiling point
Since VP increases with temp, for temperatures > ATM pressure the bp H2O > 100℃

56
Q

when is bp of H2O below 100 ℃?

A

At lower pressures

57
Q

What is Gibbs phase rule

A

F = C -P +2

F = number of degrees of freedom
C = number of components in the system
P= number of phases at equilibrium

58
Q

what do phase diagrams show?

A

they plot temperature vs pressure
*illustrates at what T/P the different (s), (l), (g) phases of matter

59
Q

What is triple point on a phase diagram?

A

The temperature and pressure at which all 3 phases co-exist (s), (l), (g)

60
Q

What is the critical point?

A

On the (l) (g) boundary, its where the boundary disapears and the substance becomes a supercritical fluid

61
Q

What are supercritical fluids?

A

They are substances that can move through objects like gases. But they dissolve things like a liquid

62
Q

Describe a CO2 phase diagram

A

*The (s) - (l) equilibrium line has a +ve slope
*(S) CO2 is denser than (l) CO2
*At 1atm, if temp increases the phase change is (s) - (g) -Sublimation
*Can’t be a liquid at P > 5.11

63
Q

Describe a H2O phase diagram

A
  • The (s) -(l) equilibrium line has a -ve slope
  • Ice is less dense than (l) water
  • As P increases, ice melts to form water because the same mass occupies less volume
    *Triple point is P=00.06ATM, T=0.01℃
64
Q

How many distinct solid phases of ice are there?

A

16

65
Q

What are polymorphs

A

Solid material can exists in different conditions in the form of different crystalline structures

66
Q

What is the phase rule?

A

F = C - P + 2

F = dof (independent variables you can change without changing No. of phases at equilibrium)
C = NO. of components in the system (Chemically independents constituent of the system)
P = No. of phases at eq.

67
Q

If,
I > II and,
UAI > UAII, is the reaction feasible?

A

dG = -UAdnA (I) + UAdnA (II)
Yes, ΔG will occur, as overall ΔG will be <0
I -> II (forward reaction)

68
Q

What is the mathematical definition of a components contribution to G in terms of U?

A

RTlnPa/P

PA = P*A Xa

PA = partial pressure of A
P*A = Vapour pressure of pure component A
XA= mole fraction of A in the mixture

69
Q

What is the calculation for UA mixture?

A

UA mixture = UA pure + RT ln XA

70
Q

What is the driving force of mixing

A

*XA < 1. so that,
*Ln XA <0. so that,
*UA is less in the mixture than the
pure gas (at constant P) =DRIVING FORCE
so , ΔG<0
= SPONTANEOUS MIXING

71
Q

What is the equation for mixing 4+ ideal gases?

A

Gfinal -Ginitial = RT/n (Sum of i) XiLnXi

72
Q

what does ni/n equal?

A

Xi

73
Q

How will the mixing of 4 gases be spontaneous?

A

if Xi < 1 , all terms in lnXi must be <0
So that 𝝙G of mixing is <0
= Spontaneous mixing
-at constant T/P

74
Q

What is the equation for ΔS of mixing

A

ΔS mixing = -(dG mixing/ dT)
= - (R/n [Sum of I] XiLnXi

ΔS = ALWAYS +ve
=Driving force , as ΔG = ΔH-TΔS

75
Q

when mixing 2 components A and B what does it mean if:
1.Mole fraction of A =1
2.Mole fraction of A =0
3.Mole fraction of a = 0.5

A

1.AAAAAA
2.BBBBBB
3.ABABAB

76
Q

For 𝝙S of mixing, what equation do we need to remember to find 𝝙G mixing

A

𝝙G mix = RT/ n x (SUM of i Xi lnXi)

Sub in to

S= -(d̂G/d̂T)P

77
Q

What are the driving forces for mixtures of non-ideal gases?

A

ALWAYS:
1. Xi<1
2. so lnXi <0
3. so 𝝙G mixing <0

78
Q

What is Raolt’s law?

A

Partial VP of each component and it’s given by:
Pi= P*I Xi

Xi = mole fraction
P*I= vp when pure

79
Q

In a mixture how do find VP

A

P= PA + PB
Add the partial pressures

80
Q

What is Euler’s number?

A

Natural log E = 2.718

81
Q

When is mixing not spontaneous?

A

Between polar and non-polar substances e.g. oil and water
* Energy lost by breaking bonds isnt compensated by maing bonds
*SO, 𝝙H mixing is +ve > +ve 𝝙S
*SO, 𝝙G = +ve
NOT SPONTANEOUS
(immiscible)

82
Q

What does the equation:
𝝙U = 𝝙Q =P𝝙 mean?

A

Expansion of gas when heated
-Work done depends on pressure in the system and change in volume
-Work done on the system depends on gas changes and pressure in the system

83
Q

What are differentials and what do they represent?

A

“differentials” refer to infinitesimal changes in thermodynamic variables, which are used to describe how a system’s properties change in response to changes in its state.
-Usually in terms of one variable in relation to another.

84
Q

If y=3X²Z⁴
And we only want to know the relationship between X and Y, what do we do?

A

We keep X constant so,

(dy/dx)z = 6XZ⁴

85
Q

What is the formula for working out differentials, if Y=aX^n

A

dy/dx = anX^n-1

86
Q

How would you get the overall change in internal energy?

A

you would add the differentials where volume is kept constant and whee temperature is kept constant

du= (d̂U/d̂T)V. dT + dU=(d̂U/d̂V)T. dV

87
Q

What is a state function?

A

It is a property whose value doesn’t depend on path taken to reach a specific value
-Conditions and history independent of value
e.g. Internal function, Entropy, Gibbs

88
Q

What is a path function?

A

path functions have values that depend on the path taken from initial state -> final state
e.g. Work, heat transfer

89
Q

What is the definition of heat capacity?

A

The ability of a system to absorb heat as a function of temp
-Energy required to heat 1g by 1K

90
Q

Enthalpy is = internal energy + (——)?

A

P x V

so H= U + PV

91
Q

In regards to entropy and specific heat what does CV equal?

A

CV = dQ/dT = T(d̂S/d̂T)v

92
Q

At melting what does 𝝙S equal?

A

𝝙S = 1/L

L = Latent hat of fusion

93
Q

At boiling what does 𝝙S equal?

A

𝝙S = L/T

L= Latent heat of vaporisation

94
Q

What is bigger latent heat of fusion or vaporisation?

A

Lv > Lf

95
Q

what is the relation ship between entropy and temperature

A

If T increases, S increases

96
Q

If dS = dQ/T and C= d̂Q/d̂T

merge these equations if relation to dS

A

dS = Cd̂T/T

97
Q

What can often hinder maximum entropy?
What equation relates to max Entropy?

A

Bonds and IM forces

S =Kb ln(W)
j.k-1mol-1

Chemistry 2 (7 decks)

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