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Chemistry Year 2 > Thermodynamics > Flashcards

Thermodynamics Flashcards

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1
Q

What is the equation for entropy change of given substance?

A

Do on iPad

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2
Q

What is the enthalpy of lattice dissociation?

A

The enthalpy change when one mole of a lattice is broken up to produce gaseous ions an infinite distance apart

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3
Q

What is the enthalpy of solution?

A

The enthalpy change when one mole of an ionic compound dissolves in sufficient water to produce a solution of infinite dilution

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4
Q

What is the enthalpy of hydration?

A

The enthalpy change when one mole of gaseous ions dissolves in sufficient water to produce a solution of infinite solution

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5
Q

What is Hess’ law?

A

If a chemical change can occur by more than one route, the overall enthalpy change for each route must be the same, provided that the starting and finishing conditions are the same

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6
Q

What is the first ionisation energy?

A

The enthalpy change when one mole of electrons is removed from one mole of gaseous atoms to produce one mole of gaseous mononuclear ions

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7
Q

Is atomisation endothermic or exothermic?

A

Endothermic as chemical bonds are always broken

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8
Q

Why is the standard enthalpy of atomisation similar for all halogens? How do they vary?

A

1) They all have single covalent bonds that are broken
2) This value decreases as halogens get larger as the forces holding the atoms together are weaker. The values for oxygen and nitrogen are larger than any of the others due to the double and triple covalent bond

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9
Q

What is electron affinity?

A

The enthalpy change when one mole of electrons is gained by one mole of gaseous atoms to produce mononuclear ions

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10
Q

What is the entropy change during a chemical reaction?

A

The difference between the total entropy values of the products and reactants

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11
Q

How can the absolute standard entropy of a substance at 298K (room temp) be calculated?

A

By measuring the temperature change as energy is transferred to the substance by heating it

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12
Q

Is the process of dissolving an endothermic or exothermic process?

A

Exothermic, as the formation of bonds between water molecules and the cations and anions releases energy

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13
Q

What is a solution of infinite solution?

A

One where adding any more water does not cause further enthalpy change, there is no observable change in temperature.

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14
Q

The enthalpy of atomisation is related to the…

A

… forces of attraction between atoms. In metals these are metallic bonds (electrostatic attraction of metal ions for delocalised electrons). In non-metals they are covalent bonds (mutual electrostatic attraction of two nuclei of shared electrons).

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15
Q

What are lattices?

A

Giant regular structures formed from ionic compounds. The regular arrangement of ions is reflected in the shape of the compounds crystals

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16
Q

When doing calculations with this equation, DO ON IPAD, what assumption is made?

A

DO ON IPAD

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17
Q

When does an exothermic change occur?

A

When forces of attraction operate e.g. in the case of electron affinity or forming an ionic lattice

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18
Q

Why are the second and third electron affinities endothermic?

A

After the first affinity, the atom becomes a negative ion, which repels the further electrons, this repulsive force must be overcome

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19
Q

Is the enthalpy of solution an endothermic or exothermic process? Give examples

A

Both:

  • NaCl dissolving in an excess of water lowers the temp of the water, it is an endothermic change
  • NaOH dissolving in a excess of water is an exothermic change, the temperature of the water rises
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20
Q

What is the lattice enthalpy of formation?

A

The enthalpy change when one mole of a crystalline compound is formed from gaseous ions scattered an infinite distance apart

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21
Q

As you go down a group, does the enthalpy of hydration increase or decrease?

A

Slightly decrease because the ionic charge is constant and the ionic size increases

22
Q

What is a more significant factor for producing larger hydration enthalpies, ionic charge or ionic size?

A

Ionic charge

23
Q

What does feasibility depend on? What is the equation to combine these?

A

1) The combination of enthalpy changes

2) do on iPad

24
Q

There are many examples where values calculated theoretically using Coulomb’s law and experimentally using BH cycles differ significantly. What is the explanation for this?

A

The bonding is not purely ionic. The bonds have some covalent character because electron clouds surrounding the negative ions can be polarised by the positive ions. The degree of covalent character and polarisation is increased by having smaller positive ions or larger negative ions

25
Q

When would the entropy value of a crystalline lattice be zero?

A

At absolute zero (0K) when the particles no longer jiggle about their positions in the lattice. They are static and a ‘perfect’ crystal is formed

26
Q

How is Coulomb’s law be used to calculate theoretical values for lattice enthalpies? What assumptions are made?

A

1) It is used to calculate the electrostatic attraction between oppositely charged ions as a function of the charges on the ions and distance between them
2) Complete electron transfer is assumed to happen when ionic bonds form. The radii of the spherical ions that form are estimated

27
Q

What is the standard enthalpy of formation?

A

Energy released during the formation of one mole of a compound from its constituent elements in their standard states under standard conditions

28
Q

When does an endothermic change occur? Give examples

A

When forces must be overcome e.g. during atomisation, ionisation or breaking up a lattice

29
Q

Are electron affinities endothermic or exothermic?

A

Can be both, exothermic for non-metals as there is a strong attractive force between their nuclei and outer electrons, produced by a relatively high charge for that period

30
Q

Why is water such a good solvent?

A

The water molecule is polar due to the difference in electronegativity between oxygen and hydrogen. The polar ends are attracted to the ions in the ionic lattice of a solid. Attractive forces between the water molecules and the ions in the lattice compete with the attractive forces between the ions in the lattice. Ions are surrounded are surrounded and carried off into solution, helped further by the KE of the moving water molecules

31
Q

As does the temperature of a system decreases, the entropy, the enthalpy of a system…

A

… decreases

32
Q

What does the value of lattice enthalpy depend on? What situation would lead to a large enthalpy of lattice formation?

A

1) - the charges on the ions
- the size of the ions
- the type of lattice formed (pattern in which they pack together)
2) greater charge on the ions, smaller ions and a closer packing in the lattice

33
Q

What is lattice enthalpy used for?

A

1) to test our ideas of ionic bonding

2) to increase understanding of why some compounds don’t exist e.g. MgCl

34
Q

What does the enthalpy of atomisation depend on?

A
  • ionic charge
  • ionic size
  • electron shielding
35
Q

What dictates feasibility? What dictates the rate of a reaction?

A

1) Thermodynamics

2) Kinetics and the energy barriers to effective collisions

36
Q

Why can’t lattice enthalpies be measured directly? How are they calculated?

A

1) It is impossible to to carry out experiments in which gaseous ions are spread out at infinite distances
2) From experimental data using the BH cycle

37
Q

What does the magnitude of the enthalpy of hydration depend on?

A

The strength of the bonds formed between the gaseous ion and water molecules. The smaller and more highly charged an ion is, the greater ta enthalpy of hydration

38
Q

As you go along a period does the enthalpy of hydration increase or decrease?

A

It increases significantly because the ionic charge increases and the ionic size decreases

39
Q

The particles of a substance are more ordered in…

A

Solids, especially crystals, than liquids. Similarly they are more ordered in liquids than gases

40
Q

What does a BH cycle allow you to do?

A

To connect experimental data to lattice enthalpy, which cannot be measured directly. Hess’ law can be applied to the cycle to calculate lattice enthalpies

41
Q

What does feasibility mean?

A

Whether or not a physical or chemical change could take place spontaneously

42
Q

What does infinite dilution mean?

A

When the limit to the number of water molecules that are bound around a cation or anion is reached

43
Q

How can entropy always increase? Give an example

A

If the entropy change of the surroundings are considered, e.g. when water vapour condenses, the entropy value in the system decreases. However condensation is an exothermic process so energy is transferred to the surroundings. When the entropy change in the system is taken into consideration, the overall entropy increase

44
Q

For covalently bonded substances when is the enthalpy of atomisation half the bond dissociation enthalpy? When is it more than half and why?

A

1) When the substances are gases under standard conditions

2) When the substances are not gases e.g. for bromine and iodine as energy is needed for change of state

45
Q

What is bond enthalpy?

A

1) The enthalpy change when one mole of covalent bonds in a gaseous element is broken, often called bond energy
2) Endothermic, energy is transferred from the surroundings to the gaseous element when covalent bonds are broken

46
Q

Dissolution may be endothermic or exothermic. What happens when a crystalline solid dissolves in water?

A

It goes from a highly ordered state to a much more disordered state. The particles (ions or molecules) are released from there fixed positions in the lattice and move freely in solution

47
Q

How can enthalpies of solution be estimated? What does the enthalpy of solution equal?

A

1) Using lattice enthalpies and enthalpies of hydration

2) The lattice enthalpy + the sum of the enthalpies of hydration of gaseous ions

48
Q

What is the standard enthalpy of atomisation?

A

The enthalpy change when one mole of gaseous atoms is formed from an element in its standard state

49
Q

What info is needed for a BH cycle of an ionic compound?

A
  • enthalpy of formation
  • ionisation energy
  • enthalpy of atomisation
  • bond enthalpy
  • electron affinity
50
Q

FEASIBILITY OF CHANGE DO ON IPAD

A

iPad

51
Q

What does agreement between values calculated by BH cycles and theoretical values provide evidence for?

A

The model of spherical ions packed together in a lattice and held together by electrostatic forces of attraction between the oppositely charged ions

52
Q

What is entropy?

A

The degree of disorder in a system, as disorder increases, so does entropy

Chemistry Year 2 (15 decks)

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