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Advanced Higher Chemistry > Unit 1 Inorganic Chemistry: Key Area 5 - Reaction Feasibilty > Flashcards

Unit 1 Inorganic Chemistry: Key Area 5 - Reaction Feasibilty Flashcards

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1
Q

What is thermochemistry?

A

The study of changes in energy which occur during chemical reactions.

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2
Q

What is the first law of thermodynamics?

A
  • The total energy of the Universe (System and Surroundings) is constant.
  • Energy can be converted from one form to another while the total energy remains the same.
  • Energy can neither be created nor destroyed.
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3
Q

What is the symbol for a standard reaction?

A

()°

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4
Q

What is standard state?

A

Most stable state of the substance under standard conditions (usually 298K = 25⁰C and pressure of 1 atm).

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5
Q

Usuwiw

A

The standard enthalpy of formation, ΔH°,is the enthalpy change when one mole of a f
substance is formed from its elements in their standard states.

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6
Q

What does the standard enthalpy of formation of elements always equal?

A

0

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7
Q

What is the equation for the standard enthalpy?

A

The standard enthalpy of formation(f) of products - reactants:

ΔH° = ΣΔH°f(products) - ΣΔH°f(reactants)

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8
Q

What do elements in their standard state have?

A

ΔH°f = 0

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9
Q

What is entropy?

A

The entropy (S) of a system is a measure of the degree of disorder of the system.

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10
Q

What does a greater degree of entropy represent?

A

A greater degree of disorder

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11
Q

What does the second law of thermodynamics state?

A

That the total entropy of a reaction system and its surroundings always increases for a spontaneous process.

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12
Q

What is the third law of thermodynamics?

A

The Third Law of Thermodynamics provides a reference against which entropies can be measured:

  • “the entropy of a perfect crystal at 0K is zero”
  • The entropy then increases as heat energy is supplied.
  • Entropy increases as temperature increases.
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13
Q

How does temperature effect entropy?

A

Entropy increases as temperature increases.

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14
Q

When is there a rapid increase in entropy and an even more rapid change in entropy?

A

There is a rapid increase in entropy at the melting point of a substance and an even more rapid and larger change in entropy at the boiling point.

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15
Q

How does entropy increase from a solid ➡️ liquid ➡️ solid?

A

The disorder increases

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16
Q

How does entropy change from smaller molecules to larger molecules?

A

Entropy increases (larger molecules have greater energy).

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17
Q

How does heat energy released by the reaction system into the surroundings affect entropy?

A

Increases the entropy of the surroundings.

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18
Q

How does heat energy absorbed by the reaction system from the surroundings affect entropy?

A

Decreases the entropy of the surroundings.

19
Q

What are the units for standard entropy?

A

JK-1 mol-1

20
Q

What is the standard entropy of a substance?

A

The standard entropy of a substance is the entropy value for the substance in its standard state.

21
Q

What is the calculation for standard entropy?

A

ΔS° = ΣΔS°(products) - ΣΔS°(reactants)

22
Q

How does entropy change when a substance is dissolved?

A

The substance has greater entropy when it is dissolved.

23
Q

How does molecular shape like linear to trigonal pyramidal affect entropy?

A

Greater vibrations in trigonal pyramidal compared to linear increases the entropy, therefore trigonal pyramidal has higher energy.

24
Q

How does mixtures affect entropy?

A

Mixtures have greater randomness and therefore increase entropy.

25
Q

What is a spontaneous reaction?

A

A reaction is said to be spontaneous if it occurs without being driven by some outside force.

26
Q

How do spontaneous reactions affect entropy?

A

Spontaneous reactions increase the total entropy of the universe.

27
Q

What are examples of spontaneous reactions?

A
  • Rusting
  • Salt dissolving
  • Ice melting
  • Fruit ripening
28
Q

How does water freezing affect entropy?

A
  • Water freezing leads to a decrease in entropy within the system.
  • Being exothermic, however, leads to an increase in entropy in the surroundings.
  • Water freezing is a spontaneous process whenever there is an overall increase in entropy.
29
Q

How does ice melting affect entropy?

A
  • Being endothermic leads to a decrease in entropy in the surroundings.
  • There must then be an increase in entropy within the system.
  • Ice melting is a spontaneous process whenever there is an Overall Increase In Entropy.
30
Q

What is the Gibbs free energy change?

A

The change in Gibbs free energy (ΔG) combines entropy and enthalpy into a single equation to describe the spontaneity of a process at constant temperature and pressure.

31
Q

What is the equation of Gibbs free energy?

A

ΔG° = ΔH° - TΔS°

32
Q

What does a ΔG<0 represent?

A

The reaction is spontaneous - Feasible.

33
Q

What does a ΔG>0 represent?

A

The reaction is non-spontaneous - Not Feasible.

34
Q

What does the T stand for in the Gibbs free energy equation?

A

Temperature in kelvin

35
Q

What does a negative value of ΔG mean?

A
  • That a reaction can happen but does not mean it will happen.
  • The reaction is thermodynamically feasible but could be kinetically unfavourable.
  • i.e. it is very slow due to a high activation energy.
36
Q

What are the 2 ways of Gibbs free energy for a feasible reaction?

A

ΔG(-) ΔH(-) TΔS(+) or ΔG(-) ΔH(+) TΔS(TΔS > ΔH)

37
Q

What are the 2 ways of Gibbs free energy for a non-feasible reaction?

A

ΔG(+) ΔH(+) TΔS(-) or ΔG(+) ΔH(-) TΔS(TΔS < ΔH)

38
Q

What is a feasible reaction?

A

A feasible reaction is one that tends towards the products rather than the reactants.

39
Q

What is the critical temperature of a reaction?

A

The temperature at which the reaction is feasible.

40
Q

What is the equation for the critical temperature of a reaction?

A

T = ΔH° / ΔS° as we take ΔG° = 0

41
Q

What is the equation for the critical temperature of a reaction?

A

T = ΔH° / ΔS°

42
Q

At what value of ΔG is equilibrium?

A

0 (when the Gibbs energy of the products is equal to the Gibbs energy of the reactants).

43
Q

What will happen to a reversible reaction until the composition is reached where ΔG = 0?

A

reversible reaction will proceed spontaneously until the composition is reached where ΔG = 0.

Advanced Higher Chemistry (6 decks)

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