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A2 Chemistry > Thermodynamics - Entropy > Flashcards

Thermodynamics - Entropy Flashcards

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1
Q

What is a feasible reaction?

A

A reaction that can occur at a particular temperature without being driven by external influences

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2
Q

Why may a feasible reaction not occur?

A

Because the activation energy is too high for it to proceed

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3
Q

For what set of values of total entropy change is a reaction feasible?

A

When delta Stotal is greater than zero

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4
Q

For what set of values of change in gibbs free energy is a reaction feasible?

A

When Gibbs free energy is less than or equal to zero

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5
Q

What is a spontaneous reaction?

A

A spontaneous reaction is one that is feasible and occurs under standard conditions

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6
Q

What are the conditions needed for a reaction to be spontaneous?

A

When Gibbs free energy is less than or equal to zero and the activation energy is low enough for the reaction to take place under standard conditions

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7
Q

What can be said about a reaction that is feasible but not spontaneous?

A

It has a high activation energy

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8
Q

What is entropy?

A

A measure of the disorder of particles (the number of arrangements particles can make)

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9
Q

What are standard entropy values?

A

The molar entropy of the pure substance in its standard state at 100kPa and the temperature of interest

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10
Q

What is the symbol for entropy?

A

S

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11
Q

What are the units of entropy?

A

JK-1mol-1

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12
Q

What is the link between the entropy value and the amount of disorder in a substance?

A

The higher the entropy value the more disordered a substance

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13
Q

What factors affect entropy?

A

State, temperature, number of moles and Mr

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14
Q

How does state affect entropy?

A

As you go from solid to liquid to gas the entropy increases

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15
Q

Why do solids have a low entropy value?

A

Very regular and ordered arrangements so there are few ways in which particles can arrange themselves

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16
Q

Why is there a larger increase in entropy between liquids to gases than solids to liquids?

A

Gases are more disordered so the particles can form more arrangements

17
Q

How does temperature affect entropy?

A

The higher the temperature the greater the entropy bc the more disordered the particles become

18
Q

How does Mr affect entropy?

A

The higher the Mr of substances in the same state the higher the entropy

19
Q

How does the number of particles affect the entropy?

A

The more particles the higher the entropy value because the more arrangements the particles can make

20
Q

What is the third law of thermodynamics?

A

At 0K there is 0 entropy bc the substance is a perfectly ordered crystalline substance

21
Q

What is the melting point?

A

The increase in entropy between the solid and the liquid

22
Q

What is the boiling point?

A

The increase in entropy between the liquid and the gas

23
Q

How do you calculate the entropy of a system?

A

Sum of entropy of products - sum of entropy of reactants

24
Q

How do you calculate the entropy of the surroundings?

A

-deltaH/temperature

25
Q

What is the second law of thermodynamics?

A

The entropy of the universe tends to increase

26
Q

How do you calculate the total entropy?

A

entropy of system + entropy of surroundings

27
Q

When the total entropy is greater than 0, what can be said about the reaction?

A

It’s feasible

28
Q

What does the feasibility of a reaction depend on?

A

Enthalpy change, entropy change, temperature

29
Q

How can Gibbs free energy be calculated?

A

enthalpy change - temperature x total entropy change

30
Q

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

A

When the Gibbs free energy is 0 so T = enthalpy change/entropy change

31
Q

What factors affect the feasibility of a reaction?

A

Whether a reaction is endo or exothermic and whether the entropy increases or decreases

32
Q

Units of delta G?

A

kJmol-1

33
Q

Units of temperature?

A

K - Kelvin

34
Q

Units of entropy?

A

JKmol-i1

35
Q

What is delta G during a change of state?

A

0

36
Q

Why is delta G positive for temperatures below melting point?

A

Reaction not feasible bc not enough energy

A2 Chemistry (17 decks)

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