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OCR A A-Level Chemistry > Chapter 22 - Enthalpy And Entropy > Flashcards

Chapter 22 - Enthalpy And Entropy Flashcards

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1
Q

What does lattice enthalpy measure?

A

The strength of the ionic bonds in a giant ionic lattice

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2
Q

What is the definition of lattice enthalpy?

A

The enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions

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3
Q

Why will the value for lattice enthalpy always be negative?

A

It is an exothermic change

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4
Q

What is the name of the cycle used to indirectly determine the enthalpy change of a reaction?

A

The Born-Haber cycle

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5
Q

What are the three different processes covered in route 1?

A

Formation of gaseous atoms
Formation of gaseous ions
Lattice formation

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6
Q

What type of reaction of the formation of gaseous atoms?

A

Endothermic - bonds are broken

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7
Q

What type of reaction is the formation of gaseous ions?

A

Endothermic

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8
Q

What type of reaction is lattice enthalpy?

A

Exothermic

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9
Q

What processes are covered in route 2?

A

The enthalpy change of formation, which is exothermic

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10
Q

What is the standard enthalpy change of formation?

A

The enthalpy change that takes place for the formation of one mole of gaseous atoms from the element in the standard state under standard conditions

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11
Q

What is the first ionisation energy?

A

The enthalpy change required to remove one electron from each atom in a mole of gaseous atoms

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12
Q

What type of reaction is ionisation energy?

A

Endothermic - energy is required to overcome the force of attraction between the nucleus and electron

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13
Q

What is the first electron affinity?

A

The enthalpy change that takes place when one electron is added to each atom in a mole of gaseous atoms

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14
Q

What type of reaction is electron affinity?

A

Exothermic - The electron being added is attracted to the nucleus

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15
Q

When are multiple ionisation energies required?

A

When the atom has more than one electron to lose

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16
Q

Why are second ionisation energies endothermic?

A

Energy must be used to ensure the negatively charged ion accepts the negatively charged electron

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17
Q

What is the standard enthalpy change of solution?

A

The enthalpy change that occurs when one mole of a solute dissolves in a solvent

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18
Q

Why does water dissolve sodium chloride?

A

Sodium chloride forms a giant ionic lattice with the Na+ ion and Cl- ion
Water consists of the H+ ion and the O2- ion
The oxygen is attracted to the sodium atom and the hydrogen is attracted to the chlorine atom
The ionic lattice becomes surrounded with water and breaks down

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19
Q

When using q=mcΔt, what is important to remember about mass?

A

It must be the mass of both the solution and the solute

20
Q

What is the enthalpy change of hydration?

A

The enthalpy change that accompanies the dissolving of gaseous ions in water to form one mole of aqueous ions

21
Q

Describe the dissolving process

A

The ionic lattice breaks up to form separate gaseous ions

The separate ions interact with the water molecules to form hydrate aqueous ions

22
Q

What characteristics do ionic compounds tend to have?

A

High melting and boiling points
Soluble in polar solvents
Conduct electricity when molten or in solution

23
Q

What are the two factors affecting lattice enthalpy?

A

Ionic charge and ionic size

24
Q

What is the effect of ionic size on lattice enthalpy?

A

The ionic radius increases
The attraction between oppositely charged ions decreases
The lattice enthalpy is less negative
The melting point decreases

25
Q

What is the effect of ionic charge on lattice enthalpy?

A

Ionic charge increases
Attraction between ions increases
Lattice enthalpy becomes more negative
Melting point increases

26
Q

If a lattice enthalpy is very exothermic, what does this indicate about the melting point?

A

The melting point will be very high

27
Q

What is the effect of ionic size on hydration enthalpy?

A

Ionic radius increases
The attraction between ion and water molecule decreases
The hydration enthalpy is less negative

28
Q

What is the effect of ionic charge on hydration enthalpy?

A

Ionic charge increases
Attraction with the water molecules increase
The hydration enthalpy is more negative

29
Q

When will a compound dissolve?

A

When the sum of the hydration enthalpies is larger than the lattice enthalpy and the reaction is exothermic

30
Q

What does a high entropy value indicate?

A

High disorder and randomness

31
Q

What is entropy?

A

The dispersal of energy within the chemicals making up a chemical system

32
Q

What are the units of entropy?

A

J K-1 mol-1

33
Q

Which state has the highest and lowest entropy values?

A 
Highest = gases
Lowest = solids
34
Q

If a chemical system changes to become more random, what happens to the value of the entropy?

A

It increases

35
Q

When there is a decrease in the number of gaseous molecules, hat happens to the entropy value and why?

A

It is negative - there is a decrease in the randomness of particles and the energy is less spread out

36
Q

What is standard entropy?

A

The entropy of one mole of a substance under standard condition

37
Q

Will standard entropies always be positive or negative?

A

Positive

38
Q

How do you calculate the entropy change?

A

(Entropy of products) - (entropy of reactants)

39
Q

What does feasibility mean?

A

If a reaction is able to happen

40
Q

What are the two types of energy making up free energy?

A

Enthalpy change and entropy change

41
Q

What is the Gibbs’ equation?

A

ΔG = ΔH - TΔS

42
Q

For a reaction to be feasible, what must the result of Gibbs’ equation be?

A

ΔG < 0

43
Q

What is important to remember about ΔS when using Gibbs’ equation?

A

Must divide by 1,000 to be in kJ

44
Q

How do you calculate the minimum temperature for feasibility?

A

Set Gibbs’ equation equal to 0

45
Q

What is the main limitation of Gibbs’ free energy equation?

A

ΔG may show that a reaction is feasible but doesn’t take into account kinetics or the rate of reaction

46
Q

Degrees to kelvin?

A

+273

47
Q

Why is entropy of water 0 at 0K?

A

As the particles are in maximum state of order

OCR A A-Level Chemistry (28 decks)

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