Thermodynamics Flashcards

1
Q

∆H

A

Heat energy exchange, enthalpy

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2
Q

Exothermic

A

-ve ∆H. Heat is released into surroundings

Therefore +ve∆T

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3
Q

Endothermic

A

+ve ∆H

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4
Q

First law

A

Total energy remains constant

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5
Q

Standard Conditions

A

100kPa pressure
298K temp
1 mol dm-3 concentration

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6
Q

∆Hr

A

For reactions in molar quantities in a chemical equation

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7
Q

∆Hc

A

Change when 1 mol reacts completely with O2

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8
Q

∆Hf

A

Change when 1 mol of compound is formed from its constituents

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9
Q

∆Hneut

A

Change when acid us neutralised by base to form 1 mol H2O

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10
Q

∆Hat

A

To form 1mol gaseous atoms

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11
Q

∆Hi.e

A

To remove 1e- per atom in 1mol gas

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12
Q

∆He.a

A

To add 1e- per atom to 1mol gaseous atoms

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13
Q

∆Hsolution

A

To dissolve 1mole of solute to form solution

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14
Q

∆Hhyd

A

To dissolve 1mole gaseous ions in water to form 1mole hydrated ions in solutions

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15
Q

Lattice enthalpy, ∆Hl.e

A

For formation of 1mol ionic compound.
Exothermic
ID indirectly by Born-Haber Cycle, and applying Hess’ Law

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16
Q

∆H Equation

A

Q=mc∆T
m= mass of surroundings
c = specific heat capacity of surroundings
∆T = temp change (final-initial temp)

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17
Q

Hess’ Law

A

If a reaction can go via +1 route, final and initial conditions are same; total enthalpy change is the same

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18
Q

∆Hc equation

A

∆H=∑∆Hc (reactants) - ∑∆Hc (products)

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19
Q

∑∆Hf

A

∆H = ∑∆Hf (products) - (reactants)

For elements, ∑∆Hf=0

20
Q

Bond enthalpy

A

Change to break 1mol of bonds

21
Q

Bond breaking vs bond making

A
Breaking = endo ∑(bond enthalpies in reactants)
Making = exo -∑(bond enthalpies in products)
22
Q

Bond enthalpy equation

A

∆H = ∑(BEs in reactants) - ∑(BEs in products)

23
Q

Small BEs

A

Break first, therefore have quick reactions

24
Q

Entropy, S

A

Measures no. of ways to arrange molecules

Increased with disorder (0K= perfect crystals and 0 entropy

25
Lattice Enthalpy factors
Ionic size and charge increase Size: decreases charge density Decreases between ion attraction Lattice energy becomes less negative
26
Ionic Charge and LE
Cation: ↑charge = more attraction ↓size =more attraction Anion: ↑charge = more attraction ↑size = less attraction
27
Hydration enthalpy factors
Charge: ↑ionic charge ↑H2O attraction
28
Hydration enthalpy factors for size
Cations: ↓size ↑H2O attraction Anions: ↑size ↓H2O attraction
29
BE equation
∆H = ∑(BEs of reactants) - ∑(product BEs)
31
Entropy equation
∆S = ∑S(products) - ∑S(reactants)
33
Free energy ∆G equation
∆G = ∆H-T∆S
34
Spontaneous (feasible) process criteria
-ve ∆G
35
-ve∆H + +ve∆S
-ve∆G
36
+ve∆H + -ve∆S
+∆G
37
-ve∆H + -ve∆S
-ve ∆G at low temps (∆H > T∆S)
38
+ve∆H + +ve∆S
-∆G at high temps | T∆S > ∆H
41
-ve ∆G and equil constant
Equil constant has large value (products predominate)
42
+ve ∆G and equil
Equil constant is small value
42
Enthalpy and entropy comparison
Lower enthalpy system = more stable one More disorderly system = more stable one -more moles also = more entropy
43
∆Ssystem
∆Ssystem = ∑S(products) - ∑S(reactants)
43
Positive v negative entropy
Positive = favour for a process
44
∆Ssurroundings
∆Ssurroundings = -(∆H/T)
44
∆G≤0 implications
∆G≤0 = feasible/spontaneous reaction Therefore ∆G MUST be negative
45
∆Stotal
∆Ssystem + ∆Ssurroundings ∆Stotal >0 = feasible process When ∆Stotal increases, so does magnitude of equil constant: ∆S = RInK
45
Temperature factors
K, not C ∆G = 0, temp is at point where reaction can become spontaneous (T = ∆H/∆S)