Energetics 15.2 Flashcards
What is Entropy ?
Entropy (S) refers to the distribution of available energy among the particles.
1) The more ways the energy can be distributed the higher the entropy.
Order of increasing entropy
solids- liquids - Gases
Factors that can change the entropy
1) Changes in temperature (Increases with temp)
2) Changes of state(freezing, evaporating)
3) Dissolving or crystallization
4) Changes in amounts of gaseous reactants or products
Factors that increase entropy (+▲S)
1) Dissolving: solids into aqueous state
2) Increase in the mol of gas
3) Note: Dissolving of gases results in a decrease in entropy
Factors that decrease entropy (-▲S)
1) Crystallization
2) Decrease in the mol of gas
Standard entropy change
Sº(products)-Sº(reactants)
1) Absolute entropy values are Sº are always +
2) Unit of Sº =JK-1mol-1
3) entropy changes (ΔS) from given standard entropy values (Sº) , ΔS (reaction) = S (products) – S (reactant).
Spontaneous process
Process that occurs without adding energy (other than the energy required to overcome the barrier)
Entropy and spontaneity
A reaction is spontaneous if the overall transformation leads to an increase in total entropy (system plus surroundings).
Spontaneous Process Entropy
▲S(total)>0
1) Positive
2) ▲S(total)=▲S(system)+▲S(surroundings)
Exothermic reaction
▲H(system) < 0 , ▲S(surroundings) >0
Endothermic reactions
▲H(system) > 0 , ▲S < 0
Second law of
thermodynamics
The second law of thermodynamics says that the ΔStotal > 0. This means
that the available probability where energy can be distributed increases! But why? First of all,
in a very macro sense, it is because universe is expanding just like the container above.
how entropy of the surroundings changes.
Simply, ΔSsurrounding is dependent on
ΔHsystem. When ΔHsystem is exothermic, then the ΔSsurrounding should increase. Conversely, when
ΔHsystem is positive, ΔSsurrounding decreases since energy is taking from the surroundings.
relationship between ΔSsurrounding and absolute temperature (K)
1) The impact of ΔSsurrounding will be dependent on the current temperature. So, if the
temperature is already very high, a small increase in entropy (due to negative enthalpy
change as mentioned above) will not make much difference. However, if the temperature is
low, a small increase in entropy will cause much difference.
2) ΔSsurrounding inversely proportional to current
temperature.
Gibbs
free energy that can do work on the system
