Reaction feasibility Flashcards
Standard enthalpy of formation
ΔH°f is the enthalpy change when one mole of a substance is formed from elements in their standard states.
Standard state of a substance
It’s most stable states at 1 atmospheric pressure and 298k (25°C)
How can the standard enthalpy of a reaction be determined?
By taking away the standard enthalpy of formation of reactants from product.
ΔH°= Ê ΔH°f(products) - ÊΔH°f(reactants)
Entropy of a system
(S) the degree of disorder with in a system
Enthalpy units
kJmol^-1
Entropy units
JK^-1mol^-1
The greater the degree of disorder within a system the …. the entropy
Greater
Solids have …… disorder, gases have….. disorder.
low,high
As temperature increases entropy…
Increases
When does rapid change of entropy of a substance occur?
At melting and boiling point boiling>melting
Second law of thermodynamics
The total entropy of a system and it’s surroundings increases in a spontaneous reaction
Third law of thermodynamics
Entropy of a perfect crystal at 0K is 0 JK^-1mol^-1
What happens when heat energy is taken in or released by a reaction system
Surrounding entropy decreases or increases
Change in standard entropy of a system
Can be calculated by taking away standard entropy of reactants from products.
ΔS°=Ê ΔS°(products) -Ê ΔS°(reactants)
Gibbs free energy equation
ΔG°= ΔH°-T ΔS°
