At temperatures lower than the boiling point, the enthalpy term predominates and ΔG is positive. That is, ΔG goes from being positive to negative and the process becomes favorable. At the temperature where this crossover occurs ΔG = 0 and ΔH = TΔS. At this temperature (373 K, 100 oC) water boils (at 1 atmosphere).

The (s) sign means that the compound is a solid. The (l) sign means the substance is a liquid. The (aq) sign stands for aqueous in water and means the compound is dissolved in water. Finally, the (g) sign means that the compound is a gas.

A chemical equation is the symbolic representation of a chemical reaction in the form of symbols and formulae, wherein the reactant entities are given on the left-hand side and the product entities on the right-hand side. The first chemical equation was diagrammed by Jean Beguin in 1615.

Delta S refers to the change of Entropy. And delta H refers to the change of enthalpy. Entropy is the variable that becomes constant in an adiabatic process.

Delta S is entropy. It’s a measurement of randomness or disorder. Notice I have deltas in front of these. That’s because we typically talk about changes, reactions or processes that actually happen in Chemistry.

If ΔH and ΔS are both positive, ΔG will only be negative above a certain threshold temperature and we say that the reaction is only spontaneous at ‘high temperatures.

A spontaneous reaction is more likely to be exothermic but can be endothermic. Non-spontaneous reactions are more likely to be endothermic but can be exothermic.

Therefore, ice has a low entropy. As ice melts, the intermolecular forces are broken (requires energy), but the order is interrupted (so entropy increases). Water is more random than ice, so ice spontaneously melts at room temperature.