Entropy Flashcards
(34 cards)
What is entropy?
A measure of disorder in a system
A measure of the number of ways energy can be shared out between particles
Symbol of entropy
S
Increase in entropy will mean…
An increase in disorder of a system
Gas made from solid, or more moles made, or more gaseous moles made
What affects the entropy of a system?
The state it’s in
Number of particles (moles)
How does the states effect entropy?
Entropy will decrease from: gases>liquid>solids as the particles are more disordered, larger distance between molecules
So if in a reaction we go from solid——> gas entropy will increase
How does number of particles affect entropy?
Entropy increases as there are more ways energy can be distributed if the no. Of moles increases
Even if the states stay the same
What does it mean for a reaction to be feasible?
Can happen spontaneously in spite of unfavourable enthalpy conditions such as low temperature
What will reactions always tend to lean towards?
More disorder thus an INCREASE in entropy
Requires less energy
Can endothermic reactions that are less enthalpically favourable still be feasible?
Yes if changes in entropy will overcome changes in enthalpy
Symbol for entropy change
🔺S
Entropy change of system symbol
🔺Sₛᵧₛₜₑₘ
How to calculate entropy change of a system of a reaction?
=total entropy of products - total entropy of reactants
By adding standard entropy values together
What are standard entropy values?
A measure of the change in entropy from natural way of order: increasing entropy (randomness)
So will always be a positive value
Units for change in entropy system
J K-1 mol-1
What do we remember when calculating the entropy change of a system?
The positive or negative sign:
Increase in entropy (positive)
Or decrease in entropy (negative)
Multiply based on molar ratio
What is the system?
The reactant molecules and product molecules
Entropy change of surroundings equation
-change in enthalpy/time
Exothermic reactions: calculating a change in entropy of surroundings
Energy is given off to surroundings so ways of arranging this energy will increase (increase in entropy)
So a negative enthalpy value is cancelled by negative in equation = positive entropy
Endothermic reactions: calculating change in entropy
Energy is transferred away from surroundings so ways of arranging this energy will decrease thus a decrease in entropy. Shown by positive enthalpy value which becomes negative by equation = negative change in entropy
What counts as the surroundings?
Solvent, container, air
To calculate the total entropy change of a reaction
Entropy change of system + entropy change of surroundings
What to make sure of when working out total entropy change?
Both units for entropy change of system + surroundings are the same
For a reaction to be thermodynamically feasible…
The total entropy change must be positive
Enthalpy change dissolving ammonium nitrate crystals in water
Endothermic
