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Combusion > Chemical TD Review > Flashcards

Chemical TD Review Flashcards

1
Q

Entropy will enable us to understand ____ energy is transferred, and free energy will help to understand _____ it can be transferred.

A

Why
when

Rogers, Chem for Eng, Pg. 319

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2
Q

What is the definition of a spontaneous process in a chemical reaction?

A

In thermal dynamics, a process is considered spontaneous if it is able to proceed on its own without being driven by an outside source of energy.

Rogers, Chem for Eng, Pg. 319

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3
Q

Any chemical reaction proceeding towards equilibrium is considered _______.

A

Spontaneous.

Rogers, Chem for Eng, Pg. 319

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4
Q

True or False

spontaneous implies that a reaction begins on its own.

A

False. Spontaneous implies that once a reaction has begun it will continue reacting without having to be driven by an outside source of energy.

Rogers, Chem for Eng, Pg. 319

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5
Q

True or False

All exothermic processes are spontaneous.

A

False. Processes that are exothermic often tend to be spontaneous, but there are many notable exceptions.

Rogers, Chem for Eng, Pg. 320

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6
Q

True or False
Processes that are exothermic, that is where the change in enthalpy is less than zero, often tend to be spontaneous. However, there are many exceptions.

A

True.

Rogers, Chem for Eng, Pg. 321

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7
Q

True or False.

Processes in which the entropy of the system increases often tend to be spontaneous. However, there are many exceptions.

A

True.

Rogers, Chem for Eng, Pg. 321

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8
Q

Entropy is a thermal dynamic function that is related to _________.

A

The number of microstates or arrangements available to a system.

Rogers, Chem for Eng, Pg. 321

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9
Q

True or False

A solid has a lower entropy than a liquid whose particles have greater freedom to move.

A

True.

Rogers, Chem for Eng, Pg. 323

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10
Q

True or False

The entropy of a gas is much lower than a solid or liquid.

A

False. The entropy of a gas is much greater than a solid or liquid.

Rogers, Chem for Eng, Pg. 323

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11
Q

For a given substance, if the temperature increases, the entropy will _____ and Delta S will be ______.

A

Increase
greater than zero

Rogers, Chem for Eng, Pg. 323

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12
Q

State the first law of thermodynamics in terms of a system.

A

The energy of an isolated system is constant.

Rogers, Chem for Eng, Pg. 324

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13
Q

What is the definition of an isolated system?

A

An isolated system is one that cannot exchange energy or matter with its surroundings.

Rogers, Chem for Eng, Pg. 324

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14
Q

What is the second law of thermodynamics?

A

The second law of thermodynamics states that in any spontaneous process the total entropy of the universe increases.

Rogers, Chem for Eng, Pg. 325

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15
Q

True or False

The total entropy of the system but not the surroundings will always increase during any spontaneous process.

A

False. The total entropy of the system and the surroundings will always increase during any spontaneous process.

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16
Q

True or False

The second law of thermodynamics states that when the entropy of a system decreases the process cannot be spontaneous.

A

False

Rogers, Chem for Eng, Pg. 325

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17
Q

The second law of thermodynamics says that the entropy of the system increases in any spontaneous process.

A

False. There are countless spontaneous processes where the entropy of the system decreases. The second law only speaks of the increase in the total entropy of the system and its surroundings.

Rogers, Chem for Eng, Pg. 325

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18
Q

Explain how a process can be spontaneous if DS_system is negative?

A

As long as DS_universe is >0, a process can be spontaneous even if DS_sys <0.

Rogers, Chem for Eng, Pg. 325

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19
Q

What is the third law of thermodynamics?

A

The third law of thermodynamics states that the absolute entropy of a pure, perfectly ordered crystalline substance at 0 Kelvin is zero.

Rogers, Chem for Eng, Pg. 325

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20
Q

What is the significance of the third law of thermodynamics?

A

All entropy values can be measured relative to the absolute zero of entropy at 0 Kelvin.

Rogers, Chem for Eng, Pg. 325

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21
Q

Define the standard entropy change for a reaction.

A

The standard entropy change for reaction, DS_rxn, is the entropy change when all reactants and products are in the thermodynamic standard states.

Rogers, Chem for Eng, Pg. 326

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22
Q

Give the four conditions required for a thermal dynamic standard state.

A
  1. Every gas exerts a partial pressure of exactly 1 atm.
  2. Every solid and liquid is in its pure form at exactly 1 atm of pressure.
  3. Every solute in a solution has a concentration of exactly 1M.
  4. The temperature is 25 degrees Celsius unless otherwise specified.

Rogers, Chem for Eng, Pg. 326

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23
Q

In an exothermic reaction heat flows from the ____ to the _______.

A

System to the surroundings.

Rogers, Chem for Eng, Pg. 327

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24
Q

Exothermic reactions _______ the entropy of the surroundings.

A

increase

Rogers, Chem for Eng, Pg. 327

25
Q

If DH_sys is <0, then DS_surr is ________.

A

Positive (>0).

Rogers, Chem for Eng, Pg. 327

26
Q

An endothermic reaction _______ heat from the surroundings.

A

Absorbs.

Rogers, Chem for Eng, Pg. 327

27
Q

During an endothermic reaction, the result is that the surroundings have a _______ kinetic energy, and therefore a ______ entropy.

A

Lower
Lower

Rogers, Chem for Eng, Pg. 327

28
Q

If DH_sys is >0, then DS_surr is ______.

A

Negative (<0)

Rogers, Chem for Eng, Pg. 327

29
Q

The magnitude of DS_surr is inversely proportional to the ______.

A

Absolute temperature.

Rogers, Chem for Eng, Pg. 327

30
Q

According to the second law of TD, a process can only be spontaneous if _________.

A

It results in an increase in the total entropy of the universe.

Rogers, Chem for Eng, Pg. 328

31
Q

What are the two reasons why the change in free energy is important in chemistry?

A
  1. It enables us to determine whether a particular chemical reaction is spontaneous or non-spontaneous.
  2. It provides a measure of the driving force of the reaction.

Rogers, Chem for Eng, Pg. 330

32
Q

DG_sys is directly realted to the change in entropy of the _________.

A

Universe.

Rogers, Chem for Eng, Pg. 331

33
Q

If Delta G <0, then the process is _______.

A

Spontaneous

Rogers, Chem for Eng, Pg. 331

34
Q

If Delta G > 0, then the process is _______.

A

Not spontaneous.

Note: However, the reverse process is in fact spontaneous.

Rogers, Chem for Eng, Pg. 331

35
Q

If Delta G = 0, then ________.

A

The system is at equilibrium.

Rogers, Chem for Eng, Pg. 331

36
Q

If Delta G for a process is negative, that process is referred to as ______.

A

Exergonic.

Rogers, Chem for Eng, Pg. 331

37
Q

If Delta G for a process is positive, that process is referred to as ________.

A

Endergonic.

Rogers, Chem for Eng, Pg. 331

38
Q

Explain how the magnitude of Delta G gives insight into the driving process behind a reaction.

A

If Delta G is negative, then the larger the negative value, the greater the driving force pushing the process forward. (and VV)

Rogers, Chem for Eng, Pg. 332

39
Q

In terms of enthalpy, when is a reaction exothermic?

A

When Delta H <0

Rogers, Chem for Eng, Pg. 332

40
Q

When is a reaction endothermic with respect to enthalpy?

A

When Delta H >0

Rogers, Chem for Eng, Pg. 332

41
Q

What is an enthalpy-driven reaction?

A

A process that is only spontaneous at relatively low temperatures.

Rogers, Chem for Eng, Pg. 332

42
Q

What is an entropy-driven process?

A

A reaction that is spontaneous only at relatively high temperatures.

Rogers, Chem for Eng, Pg. 333

43
Q

If a process is spontaneous, then Delta G is ______, and if it is not spontaneous, then Delta G is ______.

A

Negative
Positive

Rogers, Chem for Eng, Pg. 334

44
Q

Any substance spontaneously moves toward the phase that is ________.

A

Most stable at a given temperature and pressure.

Rogers, Chem for Eng, Pg. 334

45
Q

The standard enthalpy of formation of any element in its’ most stable form is always _______.

A

Zero.

Rogers, Chem for Eng, Pg. 335

46
Q

Phase change temperature always represent _______.

A

Equilibrium states.

Rogers, Chem for Eng, Pg. 337

47
Q

The Gibbs free energy function is defined such that the change in free energy under conditions of constant temperature and pressure equals _________.

A

The maximum amount of useful work that can be done on the system.

Rogers, Chem for Eng, Pg. 339

48
Q

If the change in free energy is negative, then the reaction is _______ and can _______ on the surroundings.

A

Spontaneous
do work

Rogers, Chem for Eng, Pg. 339

49
Q

When work is done on the surroundings, the sign of w is ______.

A

Negative.

Rogers, Chem for Eng, Pg. 340

50
Q

If Delta G is negative, then the reaction is ______, and the value of Delta G represents _______.

A

non-spontaneous
the minimum amount of work that must be done on the system to force a non-spontaneous event to occur at a constant temperature and pressure.

Rogers, Chem for Eng, Pg. 340

51
Q

If Delta G = -100 kJ, what is the maximum amount of useful work that can be performed on the system under constant temp and pressure conditions?

A

100 kJ

Rogers, Chem for Eng, Pg. 340

52
Q

What is a state function?

A

A state function is a property of a system that does not depend on the history of the system or the path followed during the process.

Rogers, Chem for Eng, Pg. 340

53
Q

Is the change in free energy a state function?

A

Yes, because its value is independent of how the system gets from its initial state to its final state.

Rogers, Chem for Eng, Pg. 340

54
Q

True or False

Work is a state function.

A

False. Work is path-dependent; therefore it cannot be a state function.

Rogers, Chem for Eng, Pg. 340

55
Q

What is the standard enthalpy of formation (Delta H_f^0)?

A

It is the enthalpy change that occurs when one mole of a substance is formed from its elements in their most stable form.

Rogers, Chem for Eng, Pg. 340

56
Q

What is the standard free energy of formation (Delta G_f^0)?

A

The change in free energy that occurs when one mole of a substance is formed from its elements in their most stable form.

Rogers, Chem for Eng, Pg. 340

57
Q

When a compound contains only C, H, and O and undergoes a combustion reaction with O_2, what is the result?

A

CO_2 (g) and H_20 (l)

Rogers, Chem for Eng, Pg. 341

58
Q

True or False
Delta G is very sensitive to changes in temp, while Delta H and Delta S remains fairly constant over small temperature changes.

A

True

Rogers, Chem for Eng, Pg. 343

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