Thermodynamics Flashcards

1
Q

Boyle’s equation

A

p∝1/V

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2
Q

Charles’ and Gay-Lussac’s equations

A

V∝T

p∝T

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3
Q

Ideal Gas Law

A

pV = nRT

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4
Q

1 bar in pascals

A

1 bar = 1 x 105 Pa

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5
Q

Pa in SI base units

A

kg s-2 m-1

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6
Q

0oC in kelvin

A

0oC = 273.15K

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7
Q

Dalton’s Law of Partial Pressures

A

For gases A and B:

p<sub>A</sub> = n<sub>A</sub> RT / V
p<sub>B</sub> = n<sub>B</sub> RT / V

p = pA + pB

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8
Q

Assumptions made by the Ideal Gas Law

A

The molecules take up no volume

There is no interaction between molcules

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9
Q

Van der Waals equation of State

A

p = (nRT / V-nb) - (n2a / V2)

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10
Q

For reaction A + 2B <–> C + D, what is the equilibrium constant, K?

A

|C||D| / |A||B|2

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11
Q

Symbol for internal energy change

A

ΔU

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12
Q

System definition

A

What we are interested in

eg reactants / products or biological cell

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13
Q

Surroundings definition

A

Everything else in the universe apart from the system

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14
Q

Open system definition

A

Can exchange matter and energy with surroundings

eg a beaker with ether, that is left to evaporate

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15
Q

Closed system definition

A

Can only exchange energy with its surroundings (not matter)

eg a reaction in a sealed tube

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16
Q

Isolated system definition

A

Completely insulated from surroundings (cannot exchange energy with surroundings)

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17
Q

Relationship between internal energy, U and enthalpy, H

A

H = U + pV

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18
Q

Definition of enthalpy

A

A measure of the total energy of a thermodynamic system. It includes the internal energy (sum of kinetic and potential energies), plus an additional term, pV (energy required to ‘make room for it’ by displacing its surroundings

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19
Q

1st Law of Thermodynamics

A

ΔU = q + w = ΔH - pΔV

q = heat transfer to/from surroundings
w = work done on/by surroundings
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20
Q

Work done =

A

-force x distance = -pressure x ΔV = -Δn x RT

= nRT x ln (V1 / V2)

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21
Q

Which properties depend on the path you take?

A

Heat and work

22
Q

What properties do not depend on the path taken?

  • Called state functions
A

ΔU, T, V, p, H, S, G

23
Q

For an ideal gas at a constant temperature…

A

ΔU = 0

q = -w

(𝛿U / 𝛿V)T = 0

24
Q

What is the specific heat capacity, C of a substance?

A

The amount of heat needed to raise the temperature of a substance by 1 degree

C = (𝛿q / 𝛿T) J K-1 mol-1

25
For constant pressure, ΔH =
Cp x ΔT
26
An exothermic process...
Releases heat , ΔH \< 0
27
An endothermic process...
Absorbs heat, ΔH \> 0
28
What does ΔrHo(298.15 K) mean?
Standard enthalpy change of reaction at 298.15 K
29
Define entropy
The measure of the molecular disorder of a system
30
2nd Law of Thermodynamics
The entropy of a system and surroundings increases in the course of a spontaneous change
31
Trouton's rule
Δvap S is approximately 85 J K-1 mol-1 for most liquids (NOT H2O)
32
What process is accociated with ΔHfus?
Solid to liquid
33
Entropy change for A(s) --\> B(aq) + C(aq)
Negative
34
Third Law of Thermodynamics
A perfect crystal at 0 K has zero entropy
35
Gibbs free energy, G =
H - TS (at const. p)
36
Helmholtz free energy, A =
U - TS (at const. V)
37
dG =
Vdp - SdT
38
For a reversible change, dU =
q + w
39
ΔGo =
-RTln(K) = ΔH - TΔS
40
K is always...
unitless
41
The Van't Hoff equation
(𝛿 lnK / 𝛿T) = (ΔH / RT2)
42
F, degrees of freedom that we can change independently eg temp, pressure, composition =
C - P + 2 C = chemical independent constituent P = phase
43
For calculating ΔHf at a different temperature, use the equation...
T2 ΔH = ʃ ΔCp dT T1
44
For calculating ΔS for 2 temperatures, use...
ΔS = Cp x ln(T2 / T1)
45
For calculating ΔS using ΔH, use...
ΔS = ΔH / T
46
dU =
dq + dw
47
For an instantaneous change...
dq = 0
48
At constant volume (isochoric)...
dV = 0 so dw = -pdV = 0 so ΔU = q T2 q = ʃ dq = CV x ΔT T1
49
At constant pressure (isobaric)...
dw = -pdV so Δw = -ʃ p dV so ΔU = Δq - pΔV
50
For no heat change...
H = U + pV Δq = 0 ΔU = Δw
51
Name A, B, X, Y and Z Give brief explanations of A and B
A = Critical point - cannot get transition between gas and liquid after this point B = Triple point - gas, solid and liquid are all stable at this T, p and V X = Solid Y = Gas Z = Liquid