Reaction Feasability

Question 1

What is thermochemistry

Answer 1

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

Question 2

What is the standered molar enthalpy of formation

Answer 2

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

Question 3

What is the standard state of a substance

Answer 3

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

Question 4

How is standard enthalpy formation calculated

Answer 4

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

Question 5

Whats the entropy definition

Answer 5

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

Question 6

What has low and high disorder

Answer 6

Solids have low disorder and gases have high disorder

Question 7

What happens to entropy has temperature increases

Answer 7

Entropy increases

Question 8

What does changes of state do to entropy

Answer 8

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

Question 9

Whats the second law of thermodynamics

Answer 9

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

Question 10

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

Answer 10

Increase the entropy of the surroundings

Question 11

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

Answer 11

Decreases the entropy of the surroundings

Question 12

Whats the third law of thermodynamics

Answer 12

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

Question 13

Whats an enthalpy change

Answer 13

The change in energy in a chemical reaction

Question 14

what are the two things enthalpy change can be

Answer 14

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

Question 15

Whats the standard enthalpy of formation of s compound

Answer 15

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

Question 16

Whats a standered state of an element

Answer 16

The most stable state of the substance under standard conditions

Question 17

What are standard conditions

Answer 17

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

Question 18

Where are enthalpy of formations found

Answer 18

Either in the question or the data booklet

Question 19

Whats a feasible reaction

Answer 19

A reaction that occurs at a particular temperature

Question 20

What are standard entropy values

Answer 20

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

Question 21

What is the order of entropy strength in states

Answer 21

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

Question 22

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

Answer 22

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

Question 23

What is the entropy of a perfect crystal

Answer 23

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

Question 24

What happens as entropy increases in a solid

Answer 24

The particles gain energy and vibrate more so increasing their disorder

Question 25

What happens as a solid melts to form a liquid

Answer 25

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

Question 26

When is entropy value higher between substances in the same state

Answer 26

The higher the molecular weight of substances in the same state

Question 27

Practice enthalpy and entropy question examples

Question 28

What is the total entropy change proportional to

Answer 28

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

Question 29

What is the direction of spontaneous change

Answer 29

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

Question 30

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

Answer 30

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

Question 31

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

Answer 31

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

Question 32

How is temperature at which a reaction becomes feasible calculated

Answer 32

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

Question 33

When is a reaction feasible

Answer 33

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

Question 34

When is any reaction feasible

Answer 34

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

Question 35

What will equilibrium do until /\G = 0

Answer 35

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

Question 36

What can industrial systems do

Answer 36

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

Question 37

What does the feasibility of a reaction depend on

Answer 37

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

Question 38

What is gibs standard free energy

Answer 38

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

Question 39

Whats the formula for standard free energy

Answer 39

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

Question 40

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

Answer 40

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

Question 41

What does a positive value of /\G mean

Answer 41

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

Question 42

What the difference between a reaction being feasible and spontaneous

Answer 42

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)

Question 43

What happens when /\G= 0

Answer 43

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

Question 44

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

Answer 44

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

Question 45

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

Question 46

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

Question 47

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

Answer 47

It’s the most stable form so is always 0

Question 48

When is equilibrium reached

Answer 48

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

Question 49

When has the free energy at equilibrium = 0

Answer 49

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

Question 50

Whats balance point

Answer 50

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

Question 51

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

Answer 51

Products are less favoured than reactants

Question 52

When is a standard state of a substance most stable

Answer 52

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

Question 53

Describe entropy with melting and boiling point

Answer 53

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

Question 54

What does heat energy do to entropy

Answer 54

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

Question 55

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

Answer 55

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

Question 56

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

Answer 56

Will proceed spontaneously