Unit 2) Reaction Feasibility - Free Energy Flashcards
What is used to predict the overall feasibility of a reaction
- standard free energy change
(Delta)G = (delta)H - T(delta)S
What is Gibbs standard free energy
- gibbs standard free energy is a measure of potential work that may be done by a system at constant temperature and pressure
For a reaction to be feasible G must be _____
Negative
- this is another way of stating second law of thermodynamics
The total entropy change is proportional to the change in _____ ______ of the reaction system
Free energy (G)
What are spontaneous and non spontaneous reactions
Spontaneous - a process which has a natural tendency to occur - it s thermodynamically feasible
Non spontaneous - does not have a natural tendency to occur - it is thermodynamically non feasible
If G is negative it shows that the reaction is likely to happen _______
If G is positive it shows the reaction is unlikely to happen unless external _____ is provided (until it is heated )
- Spontaneously
- energy
The direction of spontaneous change is in the direction of decreasing free energy
Difference between reaction being feasible and reaction occurring spontaneously
- a reaction may be feasible at a certain temperature (G is negative) but may not proceed due to the activation energy being too high.
- for a reaction to be spontaneous, G must be negative and the activation energy for the reaction must be low enough for the reaction to proceed under standard conditions(298K at 1atm pressure)
Calculating reaction feasibility calculations
NOTES
Temperature has major impact on the spontaneity of some reactions :
- look at summary graph in NOTES
- reactions in which enthalpy is endothermic and entropy increases
- reactions in which enthalpy is exothermic and entropy decreases
How do you calculate the temperature at which a reaction just becomes feasible - the temp at which a reaction is occurring spontaneously
Assuming G = 0 the equation can be re written as
: t = h/s
This is the temperature at which the standard free energy , G, will start to be negative and reaction will be spontaneous
Free energy and equilibrium
- at equilibrium
: both forward and the reverse reaction are ______
At equilibrium the concentration of reactants and products are ______ [not the same]
- possible
- constant
At equilibrium the system has _____ disorder
Most disorder (highest entropy)
Equilibrium and G
- if G is negative , then the reaction is thermodynamically feasible / spontaneous and the equilibrium mixture favours formation of products. So K is bigger than 1
- if G was positive then the reaction would not be feasible /non spontaneous and the equilibrium mixture would favour the reactants. K is less than 1
- if G = 0 the products and reactants would be equally favoured (g =0 at equilibrium ) K = 0
Equilibrium is reached when the free energy of the reactants has fallen to the _____ value as products
Same
At equilibrium , standard conditions do not apply so deltaG(degree) is no longer used but delta G is used instead
IMPORTANT LOOK AT BRITHT RED PAGE 43
