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Chemistry > Thermodynamics > Flashcards

Thermodynamics Flashcards

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1
Q

What is the enthalpy change of formation?

A

This is the enthalpy change when 1 mole of a compound is formed from its elements in their standard states under standard conditions

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2
Q

What is enthalpy change?

A

Enthalpy change is the heat energy transferred in a reaction at a constant pressure

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3
Q

What is the enthalpy change of atomization of an element?

A

This is the enthalpy change when 1 mole of gaseous atoms is formed from an element in its standard state

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4
Q

What is first ionisation energy?

A

This is the enthalpy change when 1 mole of gaseous 1+ ions is formed from 1 mole of gaseous atoms

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5
Q

What is first electron affinity?

A

This is the enthalpy change when 1 mole of gaseous 1- is formed from 1 mole of gaseous atoms

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6
Q

What is the enthalpy change of hydration?

A

This is the enthalpy change when 1 mole of aqueous ions is formed from 1 mole of gaseous ions

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7
Q

What is bond dissociation enthalpy?

A

This is the enthalpy change when all the bonds of the same type in 1 mole of gaseous molecules are broken

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8
Q

What is the enthalpy change of atomisation of a compound?

A

This is the enthalpy change when 1 mole of a compound in its standard state is converted to gaseous atoms.

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9
Q

What is second ionisation energy?

A

This is the enthalpy change when 1 mole of gaseous 2+ ions is formed from 1 mole of gaseous 1+ ions

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10
Q

What is second electron affinity?

A

This is the enthalpy change when 1 mole of gaseous 2- ions is formed from 1 mole of gaseous 1- ions

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11
Q

What is the enthalpy change of solution?

A

This is the enthalpy change when 1 mole of a solute is dissolved in enough solvent that no further enthalpy change occurs on further dilution

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12
Q

What is the lattice enthalpy of formation?

A

This is the enthalpy change when 1 mole of a solid ionic compound is formed from its gaseous ions under standard conditions

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13
Q

What is the lattice enthalpy of dissociation?

A

This is the enthalpy change when 1 mole of a solid ionic compound is completely dissociated into its gaseous ions under standard conditions

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14
Q

What is Hess’ law?

A

Hess’s law states that the total enthalpy change of a reaction is always the same, no matter which route is taken.

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15
Q

What is a Born-Haber cycle and why is it useful?

A

You cannot calculate a lattice enthalpy directly, so born-haber cycles are useful for figuring out the enthalpy change using another, less direct route.

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16
Q

How can you work out a theoretical lattice enthalpy?

A

You can do some calculations based on the purely ionic model of a lattice

16
Q

What is the difference in Born-Haber cycles for compounds containing a group 2 element?

A

You need one extra step
If the formation of a compound involves ions with charges of more than one you have to add the extra ionization energies and electron affinities to the Born-Haber cycle

17
Q

What is the purely ionic model of a lattice?

A

It is a model that assumes all ions are spherical, and have their charge evenly distributed around them.

18
Q

Why do you often get a different lattice enthalpy value if you do it experimentally rather than theoretically?

A

Most ionic compounds have at least a bit of covalent character

19
Q

What can we discover from the differences in experimental and theoretical lattice enthalpies for magnesium and sodium halides?

A

The values are more different for magnesium halides which shows that it is stronger than the ionic model predicts so the bonds are strongly polarised and have a lot of covalent character.
The opposite is true for sodium compounds- it is closer to be purely ionic.

20
Q

What happens when a solid ionic lattice dissolves in water?

A
  • the bonds between the ions break to free them (Endo)
  • the bonds between the ions and water are made (Exo)
21
Q

Why do water molecules bond to the ions in solution?

A

They can because oxygen in water is slightly negative so it can attact positvie ions and make bonds with them.
The hydrogen atoms are slightly positive so it can attract negactive ions and make bonds with them.

22
Q

What do most substances have to be able to dissolved and make a solution?

A

Substances generally only dissolve if the energy released is roughly the same, or greater than the energy taken in. Soluble substances tend to have exothermic enthalpies of solution.

23
Q

How do you calculate the enthalpy of solution?

A
  • lattice dissociation enthalpy
  • enthalpy of hydration
24
Q

What is entropy?

A

It is a measure of the number of ways that particles can be arranged and the number of ways that the energy can be shared out between the particles.

25
Q

What affects the entropy value?

A

The more disordered the particles are, the higher the entropy is. A large, positive value of entropy shows a high level of disorder.

26
Q

How does physical state affect entropy?

A

Solid partices only vibrate around fixed positions so they have the lowest entropy.
Gas particles move quickly and randomly in all directions so they have the highest entropy as they have the most disordered arrangement.

27
Q

How does number of particles affect entropy?

A

The more particles that you have got, the more ways they and their energy can be arranged so the higher the entropy.

28
Q

Why does a higer entropy mean more stability?

A
  • substances always tend towards disorder, and in this state they are more energetically stable.
  • this is why some reactions are feasible even when the enthalpy change is endothermic
29
Q

How do you calculate the entropy change?

A

Entropy of products - Entropy of reactants

30
Q

How can you find entropy of products and reactants?

A

Products: add up the standard entropy of all the products
Reactants: add up the standard entropy of all the reactants

31
Q

What is the standard entropy of a substance?

A

It is the entropy of 1 mole of that substance under standard conditions.

32
Q

What can an increase in total entropy mean?

A

it can mean that it is feasible for a reaction to occur, but it is not a guarantee that it will- enthalpy, temperture, and kinetics also play a part in whether or not a reaction occurs.

33
Q

What is free energy change?

A

It is a measure used to predict whether a reaction is feasible. If is negative or equal to zero, then the reaction might happen by itself. It takes into account the changes in enthalpy and entropy.

34
Q

What is the equation for free energy change?

A

Free energy change = enthalpy change - temperature x entropy change

35
Q

When are reactions feasible at any temperature?

A
  • exothermic
  • positive entropy change
  • negative free energy change
36
Q

When are reactions not feasible at any temperature?

A
  • endothermic
  • negative entropy change
  • positive free energy change
37
Q

What happens when a reaction’s free energy change is zero?

A

The reaction is just feasible

38
Q

How do you find the temperature of a reaction when the free energy change is zero?

A

T = enthalpy change/entropy change

Chemistry (22 decks)

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