The Third Law of Thermodynamics Flashcards
The Third Law of Thermodynamics states
- The entropies of all perfect crystals are zero at 0K
- There is no disorder
Why is the Third Law of Thermodynamics important
- It allows standard molar entropies S⦵ to be evaluated from measurments of heat capacity as a function of temperature
- E.g. when Cp/T is plotted on x and T on y, the area under the curve is entropy
The standard reaction entropy is the entropy chsnge associated with a chemical reaction system and can be calculated using which equation
Suggest an equation which can work out the standard entropy of a reaction at a different temperature, when standard entropy of a reaction at a first temperature is already know
*Hint Kirchhoffs’ equation
What is the equation for total entropy change
ΔStotal must be postice for the reaction to be spontaneous
If a reaction is Exothermic, ΔSsurr will be
Positive
This is because exothermic reactions give out heat, so the entropy of the surroundings will increase
If a reaction is Endothermic, ΔSsurr will be
negative
This is because, endothermic reactions take in heat so the entropy of the surroundings will decrease
When a system reacts at constant pressure, the enthalpy change is ΔH. By minusing this value, heat energy change with the surroudings can be calculated
Hence, state the equation to work out ΔSsurr
What is Gibbs Free Energy
ΔG, combines changes in enthalpy and entropy into a single state function that describes the spontaneity of a process at constant temperature and pressure
Gibbs free energy is a what function
State function
(at constant temperature)
What is the Equation for gibbs free energy
made sure ΔH and ΔS are in the same unit
A spontaneous process is accompanied by a ….. in Gibbs Free Energy, ΔG
A decrease in ΔG
What is the equation for Standard Reaction Gibbs free energy of formation, ΔfG - measures the stability of a compound
This is the standard free energy change for the formation of one mole of a compound from its elements in their most stable form
