Thermodynamics Flashcards

1
Q

Define enthalpy change

A

Heat energy change at constant pressure

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2
Q

Define enthalpy of lattice formation

A

Enthalpy change when 1 mol of solid ionic compound is formed from its gaseous ions

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3
Q

How would you calculate Entropy change for a reaction (delta S)

A

Sum of products - reactants

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4
Q

How do you calculate Gibbs free energy?

A

AG = AH - TAS

H= enthalpy change
S= entropy change
T= temp

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5
Q

When is G (gibbs) feasible and not feasible

A

G is 0 or less than 0 (negative) = feasible

G is more than 0 = not feasible

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6
Q

How would you calculate what temperature the reaction becomes feasible

A

T = AH/ (AS/1000)

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7
Q

Define enthalpy of hydration

A

Enthalpy change when one mole of gaseous ions becomes aqueous ions

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8
Q

Define enthalpy of atomisation

A

Enthalpy change when one mole of gaseous atoms is formed from a compound in its standard state in standard conditions.

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9
Q

Define electron affinity

A

Enthalpy change when one mole of gaseous atoms gains one mole of electrons to form one mole of gaseous 1- ions

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10
Q

Define mean bond dissociation enthalpy

A

Enthalpy change when one mole of covalent bonds is broken with all species in the gaseous state

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11
Q

Define enthalpy change of combustion

A

Enthalpy change when 1 mol of a compound is burned completely in O2 with all reactants and products in their standard states under standard conditions

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12
Q

What is Hess’ law

A

The enthalpy change for a chemical reaction is independent of the route taken

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13
Q

What’s the perfect ionic model

A
  • assumes bonding is 100% ionic (has no covalent character)
  • all ions are perfect spheres
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14
Q

According to the perfect ionic model, what would be the difference between LDE values

A

There would be no difference between the experimental and theoretical

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15
Q

Why does LDE decrease

A

The size of the negative ion increases

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16
Q

What does a bigger difference between LDEexp and LDEtheo mean

A

The bigger the difference between the values the more covalent character

17
Q

What effect does the covalent character have on bonds

A

It causes the strength of the bonds to increase

18
Q

What does the difference between the experimental LDE and theoretical/perfect ionic LDE mean

A
  • because there is a difference it shows there is some degree of covalent character
19
Q

How do you work out activation energy (Ea) in the Arrhenius equation

A

Ea = RT(lnA-lnk)

20
Q

If a reaction is carried out at a higher temperature how does it effect (AG) delta G

A

TAS gets bigger

21
Q

How does disorder effect entropy (delta s)

A

An increase in disorder and entropy will lead to a positive entropy change

22
Q

When will an increase in entropy occur

A
  • state change from solid/liquid to gas
  • increase in number of molecules between products and reactants
23
Q

How do AS and AH effect AG/feasibility

A
  • increased entropy (+ve AS) and exothermic (-ve AH) will make AG -ve so will be feasible
24
Q

When temp increases what happens to the feasibility if entropy (AS) decreases/is negative

A

AG is more likely positive so reaction is not feasible so won’t occur

25
Q

When temp increases what happens to the feasibility if entropy (AS) increases/is positive

A

AG is negative so reaction is feasible

26
Q

When temp increases what happens to the feasibility if entropy (AS) is 0

A

AG will not change much

27
Q

How does larger ion size effect enthalpy of formation

A
  • Bigger ion means smaller charge density
  • so enthalpy of formation will be less negative/exothermic
  • because there is a weaker attraction between ion and halide
28
Q

Define enthalpy of solution

A

Enthalpy change when 1 mol of an ionic solid is dissolved in water to infinite dilution so that the ions no longer interact under standard conditions

29
Q

Define enthalpy of lattice dissociation

A

Enthalpy change when 1 mole of an ionic crystal lattice form is separated into its constituent ions in their gaseous states

30
Q

Define enthalpy change of formation

A

The energy transferred when 1 mol of a compound is formed from its elements under standard conditions, and all reactants and products in their standard states

31
Q

Define mean bond enthalpy

A

Enthalpy change needed to break 1 mol bonds averaged over a range of molecules

32
Q

Why is electron affinity endothermic

A

The ion and the electron both have a negative charge so energy is required to overcome repulsion

33
Q

How do you work out AH from a graph

A

Y intercept

34
Q

How do you work out AS from a graph

A

gradient x 1000

35
Q

How do you work out what temperature a reaction will become feasible from a graph

A

The temperature at the X intercept and above will be feasible

36
Q

How do you work out bond enthalpy

A

Reactants - products

37
Q

What’s the difference between enthalpy of solution and hydration

A

Solution - (s) —> (aq)
Hydration - (g) —> (aq)