Enthalpy & entropy Flashcards
What is entropy, S?
A measure of dispersal of energy in a system; its a quantitive measure of the degree of disorder in a system
The greater the entropy, the _________ dispersal of energy and the ________ the disorder
Greater, greater
What does entropy do as you go from solid to liquid to gas?
Increases - it does because of the increased disorder and the more random arrangements of particles
What happens to entropy if the number of gaseous molecules in a system increases?
The entropy increases
What happens to entropy if the number of gaseous molecules in a system decreases?
The entropy decreases
What does the rule between entropy and changing number of gaseous molecules represent?
If production of gas increases, the disorder of particles increases and energy is spread out more so ΔS is positive
When would ΔS be negative?
If the number of gaseous molecules decreased
What is standard entropy, SΘ?
The entropy of one mole of a substance, under standard conditions
What are the rules of standard entropies?
- They are always negative
- They have units JK^-1 mol^-1
What is the equation for ΔSΘ?
ΔSΘ = E SΘ (products) - E SΘ (reactants)
What is feasibility?
Used to describe whether a reaction is able to take place
What is the overall change in energy during a chemical reaction called?
Free energy change, ΔG
What is the Gibbs free energy change equation?
ΔG = ΔH - TΔS
ΔG = free energy change
ΔH = enthalpy change with surroundings
T = temperature in K
ΔS = entropy change of system
What is the condition for a reaction to be feasible?
ΔG must be negative - decrease in the free energy
If ΔH is negative and ΔS is positive - is the reaction feasible?
Yes
