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A level Chemistry > Thermodynamics pt 2. > Flashcards

Thermodynamics pt 2. Flashcards

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1
Q

Why can enthalpy of solution not be measured directly?

A

Difficult to measure temp rise of solid

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2
Q

Is enthalpy of solution a chemical or physical change?

A

Physical - no new substance made

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3
Q

Why can dissolved ions no longer attract eachother?

A

Water gets in between them, so they can no longer attract eachother

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4
Q

What is the enthalpy change of solution?

A

The enthalpy change when 1 mole of ionic solid is dissolved completely in water to form an infinitely dilute solution under standard conditions

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5
Q

Why is the enthalpy of solution of some metal oxides not found in data books?

A

Metal oxides react with water to form insoluble metal hydroxides

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6
Q

Why is the bond enthalpy of NaCl not found in data books?

A

NaCl is ionic. Bond enthalpies are for covalent compounds

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7
Q

What is the enthalpy change of hydration?

A

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

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8
Q

How does water surround positive cations?

A

Water is polar.
Ion-dipole attraction between positive ion and delta- on oxygen in H2O molecules.

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9
Q

What factors affect ion-dipole attraction?

A

Ionic radius
Ionic charge

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10
Q

What type (exothermic or endothermic) of reaction would be expected from an ion-dipole attraction?

A

Exothermic
Energy released from ion-dipole attraction

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11
Q

How does ionic charge affect enthalpy change of hydration?

A

More exothermic, so stronger ion-dipole attraction, so more exothermic

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12
Q

How does ionic radius affect enthalpy change of hydration?

A

Smaller ionic radius, stronger the ion-dipole attraction, so more exothermic

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13
Q

Why can enthalpy of solution not be measured directly?

A

Difficult to measure temp of a solid

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14
Q

What is the formula for enthalpy change of solution?

A

ΔHsoln = ΔHLE + ΣΔHhyd (dissociation data given)
ΔHsoln = ΣΔHhyd - ΔHLE (formation data given)

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15
Q

What must be the condition to for a substance to dissolve in water?

A

Enthalpy change of hydration must be greater than enthalpy change of lattice dissociation ( can also dissolve by heating)

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16
Q

What is a spontaneous reaction?

A

One which proceeds on its own without any external influence

17
Q

Why are most reactions that occur freely exothermic?

A

Products are more thermodynamically stable than reactants, so spontaneous (feasible)

18
Q

Why do some spontaneous reactions not occur (even when ΔG is less than or equal to 0)?

A

Ea of reaction is too high or rate of reaction is too slow

19
Q

What is entropy?

A

The degree of disorder in a system

20
Q

What are the factors affecting entropy?

A

Dissolving - increases entropy, as particles can move more freely.
Number of moles - more particles means more entropy,
Physical state - most entropy in gasses, disorder increases as gasses have more way of arranging themselves
Ar - more electros hence more energy to distribute

21
Q

When does a substance have 0 entropy?

A

0 K

22
Q

Describe the movement of particles when the entropy of a substance is 0

A

Stationary

23
Q

Describe the arrangement of particles when a substance has an entropy of 0

A

State of perfect order

24
Q

What is the general relationship between temperature and entropy (from graph)?

A

S increases with temp
Line slopes upwards as temp increases as particles start to move

25
Q

Why does boiling lead to a larger entropy change than melting?

A

Bigger change in disorder

26
Q

Why is entropy 0 at 0 K?

A

Particles are stationary and in a state of perfect order.

27
Q

What is the formula for entropy change?

A

SPAR
ΔS = Σ(Sproducts) - Σ(Sreactants)
Positive change - increase in disorder
Negative change - decrease in disorder

28
Q

What is the equation to calculate Gibbs free energy change?

A

ΔG = ΔH - TΔS

29
Q

What does the value of ΔG tell us about a reaction?

A

If negative or equal to 0, the reaction is feasible, if positive, the reaction is not feasible

30
Q

How do you find the minimum temperature at which a reaction is feasible?

A

Set ΔG to 0

31
Q

What does a positive/negative gradient of a Gibbs graph tell us?

A

Positive - negative ΔS
Negative - positive ΔS

A level Chemistry (14 decks)

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