2b- Reaction feasibility Flashcards
What is the standard enthalpy of formation?
The enthalpy change when one mole of a substance is formed from its elements in their standard states
What is the standard state of a substance?
The substances most stable state at a pressure of 1 atmosphere and at a specified temperature, usually given as 298 K
What is enthalpy?
The energy stored in chemical bonds
What is the entropy (S) of a system a measure of?
The degree of disorder of the system
What is the relationship between the degree of disorder and the entropy?
The greater the degree of disorder, the greater the entropy
Out of solids, liquids and gases which have the highest and lowest degrees of disorder?
Gases (high disorder)
Liquids
Solids (low disorder)
What happens to entropy as temperature increases?
As temperature increases, entropy increases
At what two points is there a rapid increase in entropy?
At the melting point of a substance and then there is an even more rapid and larger change in entropy at the boiling point
What does the second law of thermodynamics state?
The total entropy of a reaction system and its surroundings always increases for a spontaneous process
Why is the entropy value useful?
Entropy can be used to calculate if a reaction will happen spontaneously
What does heat energy released by the reaction system into the surroundings do?
It increases the entropy of the surroundings
What does heat energy absorbed by the reaction system into the surroundings do?
It decreases the entropy of the surroundings
What does the third law of thermodynamics state?
The entropy of a perfect crystal at 0 K is zero
What is the standard entropy value of a substance?
The entropy value for the substance in its standard state
What can entropy be used to measure?
If a reaction can happen spontaneously
At what values is a reaction spontaneous?
When the change in entropy is positive
What is a feasible reaction?
One that tends towards the products rather than the reactants
When is a reaction said to be feasible and may occur?
When the change in free energy between reactants and products is negative
What can the feasibility of a chemical reaction under standard conditions be predicted from?
The calculated value of the change in standard free energy
The temperatures at which a reaction may be feasible can be estimated by considering the range of values of T when…?
delta G is below 0
Under non-standard conditions any reaction is feasible if…?
Delta G is negative
What is the value of delta G at equilibrium?
Zero
A reversible reaction will proceed spontaneously until what point?
The composition is reached when delta G = 0
