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

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

Gibbs Free Energy

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

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

NH4Cl (s)  NH2 (g) + HCl (g) Gibbs Free Energy Practice 1. For the reaction below, NH4Cl (s)  NH2 (g) + HCl (g) At 298.15 K, ΔH = 176 kJ and ΔS = 0.285 kJ/K. Calculate ΔG, and tell whether this reaction is spontaneous at 298.15 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?