3.1.8.2 Gibbs Free-energy Change, /\G, and Entropy Change, /\S
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What is Gibbs free energy?
It tells you the energy available for work
What is the equation for Gibbs free energy change?
∆G = ∆H - T∆S ∆G = Gibbs free energy change ∆H = enthalpy change T = temperature ∆S = entropy change
At what ∆G value does a reaction just become feasible?
Zero
Does entropy change with temperature?
Yes
What do all systems tend to go towards?
The lowest potential energy A disordered random arrangement
Define feasible
The ability of a reaction to occur
Put the states of matter in order of low entropy to high entropy
Solid < Liquid < Gas
What does a lower entropy signify?
A more ordered substance, such as solids
How does an increased number of moles affect the entropy of a reaction?
It increases it
What occurs in an endothermic reaction and how does this affect the disorder?
The system gains energy If the disorder introduced to a system is great enough, an endothermic reaction will be feasible
What is an indicator of how disordered a system is?
Systems can be given a number based on how disordered they are The higher the number the higher the disorder
Does the entropy change of a reaction show an indication about rate?
No
What does a positive Gibbs value represent?
It means that it is not feasible
What does a negative Gibbs value represent?
It means that it is feasible
Define spontaneous
Same as feasible The tendency for a reaction to happen
Define entropy
The randomness of a system Expressed mathematically Given the symbol, S
What causes a positive value of ∆S?
A reaction where the products are more disordered than the reactants
How do you work out the entropy change for a reaction?
Add all of the entropies of the products and subtract all the entropies of the reactants