2.2 Reaction feasibility Flashcards
What does this symbol mean? DH*f
the standard enthalpy of formation
What is the standard enthalpy of formation?
the energy change when one mole of a substance is formed from its elements in their standard states
What is the standard state of a substance?
the most stable state at a pressure of 1 atmosphere at a specified temperature, usually taken as 298K
How would you calculate the standard enthalpy of a reaction
ΔH° = ΣΔH°f (products) - ΣΔH°f(reactants)
What is the entropy of a system?
a measure of the degree of disorder of the system
Explain the relationship between disorder and entropy
the greater the degree of disorder, the greater the entropy
Explain disorder in the different states
-solids have low disorder
-gasses have high disorders
Explain the relationship between entropy and temperature
-entropy increases as temperature increases
-rapid increase in entropy at melting point and again at boiling point
What does the second law of thermodynamics state?
the total entropy of a reaction system and its surroundings always increases for a spontaneous process
What happens to heat energy released and absorbed by the reaction system?
-heat energy released by the reaction system into the surroundings increases the entropy of the surroundings
-Heat energy absorbed by the reaction system from the surroundings decreases the entropy of the surroundings.
What does the third law of thermodynamics state?
that the entropy of a perfect crystal at 0K is zero
What is the standard entropy of a substance?
the entropy value for the substance in its standard state
How can you calculate the change in standard entropy?
ΔS° = ΣS°(products) - ΣS°(reactants)
How would you calculate the change in free energy?
ΔG° = ΔH° - TΔS°
Explain reaction feasibility in terms of ΔG°
-If DG* negative a reaction may occur (feasible)
