Reaction Feasability Flashcards
What is thermochemistry
It is the study of of changes in energy which occur during a chemical reaction
What is the standered molar enthalpy of formation
Refers to the enthalpy change which occurs when one mole of a substance is prepared from its elements in their standered states
What is the standard state of a substance
Is its most stable state at a pressure of 1 atmosphere and a specific temperature usually 298K
How is standard enthalpy formation calculated
/\H=/\H products- /\H reactants
Whats the entropy definition
The entropy of a system is the degree of disorder of the system. The greater the disorder the greater the entropy
What has low and high disorder
Solids have low disorder and gases have high disorder
What happens to entropy has temperature increases
Entropy increases
What does changes of state do to entropy
Changes to state involves changes to entropy. Melting and evaporation are accompanied by increases in entropy
Whats the second law of thermodynamics
States that the total entropy of a reaction system and its surroundings always increases for a spontaneous process
What does heat energy released by the reaction system into the surroundings do
Increase the entropy of the surroundings
What does heat energy absorbed by a reaction system from the surroundings do.
Decreases the entropy of the surroundings
Whats the third law of thermodynamics
States that the entropy of a perfect crystal is at 0 K is zero
Whats an enthalpy change
The change in energy in a chemical reaction
what are the two things enthalpy change can be
Exothermic-heat lost to the surroundings /\H is negative
Endothermic- heat taken in from the surroundings /\H positive
Whats the standard enthalpy of formation of s compound
The energy given out or taken in when one mole of a compound is formed from its elements in their standard states
Whats a standered state of an element
The most stable state of the substance under standard conditions
What are standard conditions
Are a pressure of one atmosphere and a specific temperature usually room temp which is 298 K (25 degrees)
Where are enthalpy of formations found
Either in the question or the data booklet
Whats a feasible reaction
A reaction that occurs at a particular temperature
What are standard entropy values
Calculated for one mole of a substance based on the scale that the substance has an entropy value of zero at 0 K
What is the order of entropy strength in states
Increase in entropy from solid to liquid and another increase from liquid to gas
What are the units for entropy and where are the values found
S degrees/ k-1 mol-1 in question or booklet
What is the entropy of a perfect crystal
0 at 0 K then a general increase in entropy as temperature increases
What happens as entropy increases in a solid
The particles gain energy and vibrate more so increasing their disorder
What happens as a solid melts to form a liquid
There is a large increase in disorder at that particular temperature and is observed by a rapid vertical line
When is entropy value higher between substances in the same state
The higher the molecular weight of substances in the same state
Practice enthalpy and entropy question examples
What is the total entropy change proportional to
The change in free energy (/\G) of the reaction system
What is the direction of spontaneous change
The direction of spontaneous change is in the direction of decreasing free energy
What is the change in standard free energy related to and formula
Related to the standard enthalpy and entropy change by /\G=/\H-T/\S
What’s the formula for calculating standard free energy for a reaction
/\G=/\G(products)-/\G(reactants)
How is temperature at which a reaction becomes feasible calculated
/\H and /\S values are positive , T=/\H / /\S
When is a reaction feasible
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
When is any reaction feasible
Under non standard conditions any reaction is feasible if /\G id negative
What will equilibrium do until /\G = 0
An equilibrium reaction will proceed spontaneously in the forward direction until the composition is reached where /\G=0
What can industrial systems do
Can employ the removal of a product to force the equilibrium in the desired Direction
What does the feasibility of a reaction depend on
The enthalpy change of the reaction, the entropy change and the temperature at which the reaction is occurring
What is gibs standard free energy
Measure of the potential work that may be done by a system at constant temperature and pressure
Whats the formula for standard free energy
/\G=/\H-T/\S
What must /\G be for a reaction to be feasible
Must be equal to or less than zero this shows that the reaction is likely to happen spontaneously
What does a positive value of /\G mean
Shows that the reaction is unlikely to happen unless external energy is provided to the system
What the difference between a reaction being feasible and spontaneous
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)
What happens when /\G= 0
The system is at equilibrium so both forward and reverse reactions are feasible
What is T in the equation /\H / /\S
T is the temperature at which standard free energy, /\G will start to be negative and the reaction will be spontaneous
Practice questions !!!!!!! On standard stuff
Learn /\H,/\S,/\G table !!!!!
Wha is the standard free energy of formation of an element always
It’s the most stable form so is always 0
When is equilibrium reached
When the free energy of the reactants has fallen to the same value as the products
When has the free energy at equilibrium = 0
/\G= /\G(products) - /\G(reactats) = 0
Whats balance point
When equilibrium position exists in the middle and reactants and products are equally favoured
K=1 at this point
What does it mean when standered free energy is greater than zero
Products are less favoured than reactants
When is a standard state of a substance most stable
The standard state of a substance is its most stable state at a pressure of 1 atmosphere and at a specified temperature usually 298k
Describe entropy with melting and boiling point
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
What does heat energy do to entropy
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
What happens if the change in free energy (/\G) between reactants and products is negative
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
What will a reversible reaction do until /\G =0
Will proceed spontaneously
