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Chemistry Unit 2 How To Pass Book > Reaction Feasability > Flashcards

Reaction Feasability Flashcards

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1
Q

What is thermochemistry

A

It is the study of of changes in energy which occur during a chemical reaction

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2
Q

What is the standered molar enthalpy of formation

A

Refers to the enthalpy change which occurs when one mole of a substance is prepared from its elements in their standered states

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3
Q

What is the standard state of a substance

A

Is its most stable state at a pressure of 1 atmosphere and a specific temperature usually 298K

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4
Q

How is standard enthalpy formation calculated

A

/\H=/\H products- /\H reactants

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5
Q

Whats the entropy definition

A

The entropy of a system is the degree of disorder of the system. The greater the disorder the greater the entropy

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6
Q

What has low and high disorder

A

Solids have low disorder and gases have high disorder

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7
Q

What happens to entropy has temperature increases

A

Entropy increases

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8
Q

What does changes of state do to entropy

A

Changes to state involves changes to entropy. Melting and evaporation are accompanied by increases in entropy

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9
Q

Whats the second law of thermodynamics

A

States that the total entropy of a reaction system and its surroundings always increases for a spontaneous process

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10
Q

What does heat energy released by the reaction system into the surroundings do

A

Increase the entropy of the surroundings

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11
Q

What does heat energy absorbed by a reaction system from the surroundings do.

A

Decreases the entropy of the surroundings

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12
Q

Whats the third law of thermodynamics

A

States that the entropy of a perfect crystal is at 0 K is zero

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13
Q

Whats an enthalpy change

A

The change in energy in a chemical reaction

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14
Q

what are the two things enthalpy change can be

A

Exothermic-heat lost to the surroundings /\H is negative
Endothermic- heat taken in from the surroundings /\H positive

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15
Q

Whats the standard enthalpy of formation of s compound

A

The energy given out or taken in when one mole of a compound is formed from its elements in their standard states

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16
Q

Whats a standered state of an element

A

The most stable state of the substance under standard conditions

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17
Q

What are standard conditions

A

Are a pressure of one atmosphere and a specific temperature usually room temp which is 298 K (25 degrees)

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18
Q

Where are enthalpy of formations found

A

Either in the question or the data booklet

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19
Q

Whats a feasible reaction

A

A reaction that occurs at a particular temperature

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20
Q

What are standard entropy values

A

Calculated for one mole of a substance based on the scale that the substance has an entropy value of zero at 0 K

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21
Q

What is the order of entropy strength in states

A

Increase in entropy from solid to liquid and another increase from liquid to gas

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22
Q

What are the units for entropy and where are the values found

A

S degrees/ k-1 mol-1 in question or booklet

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23
Q

What is the entropy of a perfect crystal

A

0 at 0 K then a general increase in entropy as temperature increases

24
Q

What happens as entropy increases in a solid

A

The particles gain energy and vibrate more so increasing their disorder

25
Q

What happens as a solid melts to form a liquid

A

There is a large increase in disorder at that particular temperature and is observed by a rapid vertical line

26
Q

When is entropy value higher between substances in the same state

A

The higher the molecular weight of substances in the same state

27
Q

Practice enthalpy and entropy question examples

A
28
Q

What is the total entropy change proportional to

A

The change in free energy (/\G) of the reaction system

29
Q

What is the direction of spontaneous change

A

The direction of spontaneous change is in the direction of decreasing free energy

30
Q

What is the change in standard free energy related to and formula

A

Related to the standard enthalpy and entropy change by /\G=/\H-T/\S

31
Q

What’s the formula for calculating standard free energy for a reaction

A

/\G=/\G(products)-/\G(reactants)

32
Q

How is temperature at which a reaction becomes feasible calculated

A

/\H and /\S values are positive , T=/\H / /\S

33
Q

When is a reaction feasible

A

A reaction is feasible under standard conditions if the change in standard free energy between reactants and products is negative. Meaning equilibrium composition favours product over reactants

34
Q

When is any reaction feasible

A

Under non standard conditions any reaction is feasible if /\G id negative

35
Q

What will equilibrium do until /\G = 0

A

An equilibrium reaction will proceed spontaneously in the forward direction until the composition is reached where /\G=0

36
Q

What can industrial systems do

A

Can employ the removal of a product to force the equilibrium in the desired Direction

37
Q

What does the feasibility of a reaction depend on

A

The enthalpy change of the reaction, the entropy change and the temperature at which the reaction is occurring

38
Q

What is gibs standard free energy

A

Measure of the potential work that may be done by a system at constant temperature and pressure

39
Q

Whats the formula for standard free energy

A

/\G=/\H-T/\S

40
Q

What must /\G be for a reaction to be feasible

A

Must be equal to or less than zero this shows that the reaction is likely to happen spontaneously

41
Q

What does a positive value of /\G mean

A

Shows that the reaction is unlikely to happen unless external energy is provided to the system

42
Q

What the difference between a reaction being feasible and spontaneous

A

A reaction is feasible a particular temperature but may not proceed due to the activation energy being too high
For a reaction to be spontaneous /\G must be less than 0 and the activation energy must be low enough for the reaction to proceed under standard condition (298K and 1atm pressure)

43
Q

What happens when /\G= 0

A

The system is at equilibrium so both forward and reverse reactions are feasible

44
Q

What is T in the equation /\H / /\S

A

T is the temperature at which standard free energy, /\G will start to be negative and the reaction will be spontaneous

45
Q

Practice questions !!!!!!! On standard stuff

A
46
Q

Learn /\H,/\S,/\G table !!!!!

A
47
Q

Wha is the standard free energy of formation of an element always

A

It’s the most stable form so is always 0

48
Q

When is equilibrium reached

A

When the free energy of the reactants has fallen to the same value as the products

49
Q

When has the free energy at equilibrium = 0

A

/\G= /\G(products) - /\G(reactats) = 0

50
Q

Whats balance point

A

When equilibrium position exists in the middle and reactants and products are equally favoured
K=1 at this point

51
Q

What does it mean when standered free energy is greater than zero

A

Products are less favoured than reactants

52
Q

When is a standard state of a substance most stable

A

The standard state of a substance is its most stable state at a pressure of 1 atmosphere and at a specified temperature usually 298k

53
Q

Describe entropy with melting and boiling point

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

54
Q

What does heat energy do to entropy

A

Heat energy released by the reaction system to the surroundings increases entropy of the surroundings
Heat energy absorbed by the reaction system from the surroundings decreases the entropy of the surroundings

55
Q

What happens if the change in free energy (/\G) between reactants and products is negative

A

A reaction may occur and the reaction is said to be feasible. A feasible reaction is one that tends towards the products rather than the reactants

56
Q

What will a reversible reaction do until /\G =0

A

Will proceed spontaneously

Chemistry Unit 2 How To Pass Book (3 decks)

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