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CHEM2017 - Physical Chem > Thermodynamics > Flashcards

Thermodynamics Flashcards

(80 cards)

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1
Q

What is the internal energy theory

A

energy in the universe is always constant so if a system looses energy the surroundings gain the same amount

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2
Q

What is enthalpy

A

at constant pressure, the cahneg in enthalpy is the heat the system takes in

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3
Q

give the equation linking H, PV and U

A

H = U+ PV

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4
Q

What happens to Helmholtz energy in a reaction with a constant volume

A

the system will minimise A

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5
Q

How is Helmholtz energy related to internal energy and give equation

A

both used at constant volume, A=U-TS

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6
Q

How is Gibbs energy related to enthalpy

A

both used at constant pressure

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7
Q

What does it mean if Gibbs energy is negative

A

if a reaction has a negative Gibbs energy, the reaction is spontaneous

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8
Q

What is chemical potential

A

Gibbs energy per mole, G=N x u

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9
Q

What is entropy

A

Measure of disorder which tells us how likely something is to exist by chance

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10
Q

How does heat effect entropy

A

adding heat to a system increases its entropy

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11
Q

What is equilibrium

A

Condition under which no spontaneous overall change will occur

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12
Q

Give an example of a spontaneous change that leads to a decrease in entropy of the system and explain why this happens

A

Condensation happens spontaneously, entropy is decreased as liquid formed from gas, this is thermodynamically favourable because its an exothermic reaction so releases heat into the surroundings, increasing the surrounding entropy

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13
Q

What is an extensive property

A

extensive properties are proportional to amount of substance present, like internal energy and volume

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14
Q

what is an intensive property

A

intensive properties are independent of the amount of substance, like temperature and molar volume

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15
Q

What does increasing the pressure do to G, A, S and U

A

increasing the pressure will increase G and A, decrease S, but U is unpredictable

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16
Q

What does increasing the temperature do to U, H, S, G

A

increases the internal energy, enthalpy and entropy but decreases G due to G=H-TS

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17
Q

How can volume be used as an intensive property?

A

Volume by itself is an extensive property as it depends on amount of substance present but if you take Molar Volume, V/n it becomes intensive

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18
Q

Name some extensive properties

A

Volume, Mass, Moles, Internal Energy, Enthalpy and Heat Capacity

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19
Q

Name some intensive properties

A

Molar Volume, Temperature, Density, Pressure

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20
Q

What does ideal mixing mean and when is it often seen? What happens to H upon mixing

A

means interaction energy between molecules doesn’t change, meaning enthalpy doesn’t change, often seen when interactions are of a similar type

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21
Q

How do you work out mole fractions

A

Xa= moles of a /total moles

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22
Q

What happens to entropy in an ideal mixtures and why

A

change in entropy of a mixture is always positive as its always random

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23
Q

What happens to volume upon mixing

A

change of volume of a mixture equals zero as it can be neglected

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24
Q

What happens to enthalpy under non-ideal mixing

A

Enthalpy under non ideal mixing does not stay the same unlike ideal mixing, so mixing could be exothermic/endothermic

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25
What happens to change in G during mixing
change in gibbs energy on mixing should be negative, if its positive, means there is no mixing
26
What can the Gibbs-Duhem equation be used for
applied to changes in composition of mixture, used to work out change in chemical potential of A if B is known
27
How do you predict if mixing will be ideal or non ideal
ideal mixtures will have simmilar bonding like polarity, VDWs, Ionic/metal, most gas mixtures will be ideal though
28
What is an equation of state
expresses one thermodynamic quantity as a function of others
29
What does polymorphs mean on a phase diagram
many solid phases
30
What is an excess quantity
difference from an ideal gas
31
What is a supercritical fluid
phase that resembles both liquid and gas
32
What is the triple point on a phase diagram
where all three phases are at equilibrium
33
What does a and b mean in the Van der Waals equation of state
b means molecular size, a means attraction between molecules
33
What is the phase rule?
F+P=C+2 P means number of phases, c means number of independent components, f means number of degrees of freedom
33
What does F mean in the phase rule
F is the number of variables (degrees of freedom) that can be varied independently to keep P different phases at equilibrium
33
What do T/V and P/V phase diagrams show
they show the two phase regions where two phases are at equilibrium at either constant pressure or temp
33
What do the meanings of the possible F values mean
0 degrees of freedom means a point on the diagram, 1 degrees of freedom shows a line on phase diagram means that temp and pressure dependent on each other, 2 degrees of freedom mean that temperature and pressure can be varied independently
34
What is vapour pressure
pressure of gas at equilibrium
35
what is the change in gibbs energy for a phase change in equilibrium?
Change in Gibbs =0 for a phase change at equilibrium
36
What is latent heat? give equation
the molar enthalpy, change in Hm = T x change in Sm, found through Gibbs equation as at equilibrium, change in G=0
37
What happens to the chemical potential of the phases on phase lines
chemical potential is the same for both phases as they are in equilibrium, occurring at constant temp and pressure
38
Why is the liquid solid line on P/T phase diagram usually steeper than other lines
entropy increases from solid to liquid and but volumes of solid and liquids are smaller, follows this rule
39
Which lines on a phase diagram can be used to visualise plots of vapour pressure against temp
solid/gas lines or liquid/gas lines are plots of vapour pressure against temperature
40
What is the entropy change of the universe at equilibrium
at equilibrium, the change will always be 0
41
show the integral of the Cassius-Clapeyron equation, how can this be used
Ln(p)= - DeltaHm/RT +constant, used when molar enthalpy is constant
42
explain how the phase rule applies to different regions, lines and points on the phase diagram of a one component system
the phase rule is, F=2+C-P so with one component, F=3-P. with one phase has 2 degrees of freedom so temp and pressure can be varied independently, 2 phases in equilibrium has 1 degrees of freedom so pressure depends on temp and vice versa, this represents line on phase diagram. three phases in equilibrium have no degrees of freedom, this applies to points on a phase diagram
43
What is Raoults law applied to
used with ideal liquid mixtures in equilibrium with ideal gasses
43
What does the asterisks mean in raoults law
indicates pure liquid
44
When liquid and gas are at equilibrium, what will happen to their chemical potentials
chemical potential of liquid is equal to chemical potential of gas at equilibrium
45
What are the 3 assumptions that raoults law involves
assumes liquid mixtures and gasses are ideal, predicts that plots of partial and total pressure versus mole fraction are straight lines
46
Draw a pressure composition diagram
look at thermodynamic notes
47
What law is used with Non-Ideal mixtures
henrys law used with non ideal mixtures which vary from Raoults law, used with small concs of A in solution B.
48
What is elevation of boiling point? why does this happen
when the boiling point of solvent is increased by addition and solvation of solute. this is because the chemical potential of the solvent decreases
49
What are the three components for a mixture phase diagram and so which phase diagrams do we see with mixtures
temperature, pressure and composition, x so see them as 3D, so we see temp against composition diagrams and pressure against composition diagrams between liquid and gas.
50
When is the lever rule used and what is it?
used if bulk composition is in equilibrium, 2 phase region. horizontal line drawn across two phase region, the end points give the compositions of the two phases at equilibrium. nL/nG= dG/dL
51
What is fractional distillation
mixture heated until starts to evaporate and the vapour usually has different composition to liquid. vapour is collected and recondensed into separate container. produces liquid with higher concentration of most volatile component. repeating will concentrate it further
52
What is an azeotrope
mixture of 2 or more liquids that has a constant boiling point
53
how are raoults law and henrys law used together
for a mixture with small concentration of A in solvent B, Raoults law often used to find solvents values and henrys law used to find solute A values
54
What is important about the value of K in Henrys law?
It can take any value as its a constant, K changes when A or B changes and K also depends on the temperature. larger K means smaller solubility
55
What does Henrys law predict
predicts straight line on a P/x phase diagram showing the 2-phase region
56
Define activity in standard state
u=u(standard)=1a
57
Why does water expand on freezing but benzene doesnt?
Water expands on freezing because the water molecules dont freeze in perfect formation, they have gaps between them, making ice less dense than water. Benzene follows typical molecular behaviour so when it freezes the molecules become tightly closed packed together
58
What is the reaction quotient defined as?
defined at any point in reaction as product of activity of products/ product of activity of reagents
59
What happens to Q and change in G at equilibrium
at equilibrium, Q is called the equilibrium constant, K, DeltaG=0
60
What does K depend on
equilibrium constant, K depends on temperature but not starting concentrations or pressures.
61
in the standard state, what is Q
in standard state, Q = 1
62
What is extent of reaction
look at Thermo notes for walk through
63
What is the difference between molecules at the surface and molecules in the bulk
they do not have the same surroundings so will have different energy if liquid surface in contact with gas, surface molecules will be higher in energy than bulk molecules, if liquid surface in contact with glass, the molecules at surface will have lower energy than bulk molecules
64
What does change in energy caused by forming a surface depend on
depends on area of surface formed
65
how do you find Energy of surface tension
Esurface= surface tension x area of surface
66
how do you find the total internal energy of liquid
Utotal= Ubulk + Esurface
67
What does surface energy depend on? What does negative/positive surface tensions mean?
surface tension depends on substances at each side of surface. negative surface tension energy means that forming the interface is favourable positive means that forming interface is not favourable
68
How does capillary action work
liquid will rise up capillary tube if surface tension between liquid and glass is less than 0 as its favourable to form the interface. so surface force balances gravitational force
69
Why can small objects that are denser than water float?
Gravitational forces pull the sphere(object) down but surface force will push the sphere against gravity. with small spheres surface energy will be larger than gravitational force so sphere will float will not work with large/heavy spheres
70
How do bubbles exist in liquid
bubbles have high pressure inside of them expanding the bubble, which is larger than the pressure of the surface tension force pushing against the bubble to try and shrink it smaller bubbles have larger inside pressures, which is why boiling water bubbles.
71
Whats the relationship between expansion work and surface area change at equilibrium
they are equal as theyre in equilibrium
72
What is Q in context of statistical thermodynamics
Q=partition function, NOT REACTION QUOTIENT
73
what is n in context of boltzmann distribution
n=total number of molecules n(i)= number of molecules in energy level i
74
How can finding Q be useful for finding other thermodynamic quantities
Q can be converted into Helmholtz energy which ca be used in normal thermodynamic equations A=-KbTLn(Q)
75
What is Helmholtz energy equal to
A=U-TS=G-PV

CHEM2017 - Physical Chem (5 decks)

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