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Chemistry > Chapter 22 > Flashcards

Chapter 22 Flashcards

1
Q

What is lattice enthalpy?

A

A measure of the ionic bonding strength in a giant ionic lattice. It is the enthalpy change when one mole of an ionic compound is formed from its gaseous ions understand standard conditions.

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2
Q

Is lattice enthalpy endothermic or exothermic?

A

Exothermic as it involves bond formation (it will always be -ve)

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3
Q

What is the first route of finding a lattice enthalpy using a Born Haber Cycle?

A

Formation of gaseous atoms- changing elements from their standard states into gaseous atoms
Formation of gaseous ions - Changing gaseous atoms into +ve and -ve gaseous ions (endothermic)
Lattice Formation - changing gaseous ions into their solid ionic lattice (lattice enthalpy and exothermic)

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4
Q

What is the second route of finding a lattice enthalpy using a Born Haber Cycle?

A

Convert elements in their standard states directly into ionic lattice with only one enthalpy change (enthalpy change of formation which is exothermic)

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5
Q

What is standard enthalpy change of formation?

A

The enthalpy change when one mole of a compound is formed from its elements under standard conditions with all reactants and products in their standard states.

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6
Q

What is standard enthalpy change of atomisation?

A

The enthalpy change for the formation of one mole of gaseous atoms from the element in its standard state under standard conditions.

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7
Q

What is the first ionisation energy?

A

The enthalpy change required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions.

ENDOTHERMIC- Energy is needed to overcome the attraction between the negative electron and a positive nucleus.

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8
Q

What is the first electron affinity?

A

The enthalpy change which occurs when one electron is added each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions.

EXOTHERMIC- as the electron is attracted to the nucleus.

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9
Q

What does electron affinity measure?

A

The energy to gain electrons

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10
Q

What does ionisation energy measure?

A

The energy to lose electrons

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11
Q

Describe the dissolving process?

A

It’s when water molecules can break giant ionic lattice structures and overcome strong electrostatic attraction between positively charged ions.

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12
Q

What is enthalpy change of solution?

A

Overall energy change associated with the dissolving process.

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13
Q

What is the standard enthalpy change of solution?

A

It is the enthalpy change which takes place when one mole of a solute dissolves in a solvent. If the solvent is water the ions from the ionic lattice are surrounded by water molecules

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14
Q

Is enthalpy change of solution exothermic or endothermic?

A

It can be either it just depends on the lattice enthalpy and enthalpy change of hydration.

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15
Q

What are the ions like in a solid lattice?

A

The positive and negative ions are attracted together in a giant ionic lattice.

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16
Q

What are the ions like when the compound is an aqueous solution?

A

The positive and negative ions are separate but a surrounded by water molecules.

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17
Q

How do you calculate energy change?

A

q= m x c x change in temperature

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18
Q

In sodium chloride what is the delta minus and plus atoms attracted to?

A

The Delta minus hydrogen atom is attracted to the positive sodium. That out of plus hydrogen atom is attracted to the negative chloride.

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19
Q

Describe the experiment which determines the enthalpy change of solution?

A
  1. Weigh an empty polystyrene cup and weigh out a sample of KCl.
  2. Add 25 cm³ of water to the cup and measure the temperature of the water.
  3. Add KCl into the cup star and record the maximum temperature.
  4. Weigh the cup and the final solution.
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20
Q

How do you calculate enthalpy change of solution?

A

q (kJ)/ n

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21
Q

What are the two processes which take place when a solid ionic compound dissolves in water?

A
  1. The ionic lattice breaks up (energy is required to overcome the electrostatic attraction).
  2. Water molecules attract and surround the ions (energy released).
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22
Q

What are the two types of energy changes involved involved in the enthalpy change of solution?

A

The lattice enthalpy and the standard enthalpy change of hydration.

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23
Q

What is lattice enthalpy?

A

Enthalpy change when one mole of an ionic compound is formed from gaseous ions when under SC

ALWAYS EXOTHERMIC

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24
Q

What is standard enthalpy change of solution?

A

Enthalpy change when one mole of aqueous ions is formed from one mole of gaseous ions under SC

ALWAYS EXOTHERMIC

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25
Q

What is the general properties of ionic compounds?

A

High melting and boiling point, soluble in polar solvents, conduct electricity in molten or aqueous solutions.

26
Q

What do lattice enthalpies depend on?

A

Ionic size and ionic charge.

27
Q

What happens with the smaller the ion?

A

The great its charge, the more strongly it will attract oppositely charged ions leading to a more negative lattice into pain (ion size decreases along a period)

28
Q

What is the lattice enthalpy magnitude a good indicator for?

A

Ionic compounds melting point but other factors like packaging of ions need to be considered

29
Q

What happens when ionic charges increase for lattice enthalpy?

A

Attraction between ions increase with lattice enthalpies becoming more exothermic.

30
Q

What happens to lattice enthalpy when the ionic radius increases?

A

Attraction between ions decreases with lattice and to be becoming less exothermic therefore melting point decreases.

31
Q

What do the value of hydration enthalpy depend on?

A

Ionic size and ionic charge

32
Q

What happens as the island gets smaller in terms of hydration enthalpies?

A

The greater its charge the more strongly it will attract water molecules leading to a more negative hydration enthalpy.

33
Q

What happens when ionic charges increase for hydration enthalpy?

A

The attraction with water molecules increases so becomes more negative.

34
Q

What happens when ionic size increase for hydration enthalpy?

A

As ionic radius increases the attraction between ions and water molecules decrease. Hydration energy is less exothermic.

35
Q

How can you calculate solubility?

A

-lattice enthalpy + sum of hydration enthalpy

36
Q

What happens if the magnitude of lattice enthalpy is less than the magnitude of the sum of hydration?

A

The enthalpy of solution would be exothermic – compound would be soluble

37
Q

What happens if the magnitude of lattice enthalpy is greater than the magnitude of the sum of hydration?

A

They have to pay solution would be endothermic – the more endothermic it is the less likely it is to dissolve. These considerations don’t provide a full picture (need entropy and temperature)

38
Q

Why can trends in solubility be difficult to predict?

A

As the same factors (high charge in small size) makes lattice enthalpy more exothermic and enthalpy of hydration more exothermic.

39
Q

What is entropy?

A

It is the term used for the dispersal of energy and disorder within the chemicals making up the chemical system. Units J-1K-1 mol.
It is a natural tendency for energy to spread out rather than staying in one place.

40
Q

What happens when there is a greater entropy?

A

The greater the dispersal of energy and the greater the disorder. Systems which are more chaotic have a higher energy.

41
Q

How big is the entropy for solids?

A

They have the smallest entropy

42
Q

How big is the entropy for liquids?

A

They have a greater entropy than solids

43
Q

How big is the entropy for gases?

A

They have the greatest entropy

44
Q

What happens at 0 K in terms of entropy?

A

There would be zero energy so all substances would have an entropy value of zero.

45
Q

What happens above 0 K?

A

Angie becomes dispersed among the particles and all substances have a positive entropy.

46
Q

What happens if a system changes to become more random (a gas)?

A

Energy can spread out more. Entropy will be positive

47
Q

What happens if a system changes to become less random?

A

Energy becomes more concentrated. Entropy will be negative.

48
Q

How can you predict when entropy increases or decreases?

A

By comparing physical state of the molecules on either side of the equation

49
Q

What happens to entropy when there is a change in state?

A

Entropy increases during changes of state which gives a more random arrangement of particles.
Solid –> Liquid –> Gas
Changing from solid to liquid to gas increases entropy. Melting and boiling increases the randomness of the particles. Energy is more spread out and the entropy is positive.

50
Q

What happens when a gas is produced in terms of entropy?

A

It increases the disorder of the particles with energy spreading out more so there is a positive entropy.

51
Q

What is the standard entropy of a substance?

A

The entropy of one mole of the substance under standard conditions (100 kPa and 298 K). Units = J-1K-1mol

These are always positive

52
Q

How do you calculate entropy change?

A

PRODUCTS - REACTANTS

53
Q

What happens in terms of entropy when there is more gaseous moles on the left-hand side on the right hand side?

A

There is a decrease in the randomness of particles. Energy is less spread out and the entropy is negative.

54
Q

What is free energy change?

A

It represents the overall change in energy during a chemical reaction or process. It takes into account two types of energy:

  1. The entropy change – heat transfer between the chemical system and the surroundings.
  2. The dispersal of energy within the chemical system itself it is related to the enthalpy change of the system.
55
Q

What is Gibbs equation?

A

G= H- TS

56
Q

When is a reaction energetically feasible or spontaneous?

A

When the free energy change is negative

G < 0

57
Q

What are the limitations with free energy change?

A

It doesn’t tell you anything about the kinetics (rate) of the reaction. If the activation energy is high direction will be slow so seem like nothing is happening.

58
Q

When calculating free energy change what do you have to do to the entropy change of system value?

A

divide by 1000

59
Q

What is the equation to find out the minimum temperature feasibility?

A

T= H/S

60
Q

What unit is temperature in in the Gibbs equation?

A

Kelvin.

Chemistry (23 decks)

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