Cold packs get cold when a salt mixes with water.
No, the probability of that arrangement is very very small. The more likely arrangement is 90 people more or less randomly distributed in the room. This arrangement is more probable and we could quantitate this more probable arrangement in terms of entropy. The entropy must be included to predict if a reaction will be spontaneous. A reaction is spontaneous if G is negative, that is, the products have a lower Gibbs free energy than the reactants.