1. Gibbs Free Energy
-most chemical reactions are exothermic since releasing energy will allow products to have a lower energy state
-there is a tendency for nature to proceed in a direction that increases the randomness of a system
ex: think diffusion
-with more energy, randomness increases
ex: solid vs liquid vs gas

2. Gibbs Free Energy
-entropy is the degree of randomness of particles within a system
-processes in nature are driven in two directions: toward the least enthalpy (heat energy) and toward the largest entropy (randomness); this happens spontaneously or naturally
-often, these two are aligned, but what happens if exothermic reactions produce more order or if endothermic reactions produce more randomness?
-there is an equation we can use to determine whether a reaction will occur spontaneously given the heat transferred (enthalpy), its tendency toward randomness (entropy), and its temperature

3. Gibbs Free Energy

4. Gibbs Free Energy Note: temperature must be in Kelvin
-the free energy tells us whether or not a reaction will happen at a given temperature given its heat and randomness
-a negative number means a spontaneous and
naturally occurring reaction
-a positive number means a reaction is not spontaneous
and does not naturally occur at that temperature

5. Spontaneous at Lower Temperatures Spontaneous at Higher Temperatures
Gibbs Free Energy ΔH ΔS ΔG – +
Always Spontaneous
Spontaneous at Lower Temperatures
Spontaneous at Higher Temperatures
Never Spontaneous

6. NH4Cl (s)  NH2 (g) + HCl (g)
Gibbs Free Energy Practice
1. For the reaction below,
NH4Cl (s)  NH2 (g) + HCl (g)
At K, ΔH = 176 kJ and ΔS = kJ/K. Calculate ΔG, and tell whether this reaction is spontaneous at K.
2. For the vaporization reaction,
Br2 (l)  Br2 (g)
ΔH = 31.kJ and ΔS = 93 J/K at a temperature of 70°C. Will this reaction be spontaneous at that temperature?