Liquid intelligence the art and science of the perfect cocktail

The tug of war works like this: heat energy always wants to freeze your ice cube; entropy always wants to melt your ice cube. The relative power of these two contestants is determined by temperature. When you are making a cocktail, the tug of war always ends in a tie, but where it ends—the freezing temperature—can change.

Heat—the Lazy One: When I say heat, I don’t mean temperature. Heat is not the same as temperature. To melt ice, you add heat but you don’t change its temperature. Ice begins to melt at 0° and stays at 0° until it has completely melted, even though you are constantly adding heat energy to break water molecules free from their icy crystal prisons. Heat is a form of energy. Temperature is merely a measure of the average speed of the molecules within a substance. People often confuse these terms because to increase the molecules’ speed—to increase temperature—you add heat.

When water freezes, it gives off heat. The heat that the ice gives off is what your freezer absorbs. Because ice gives off heat as it freezes, the internal energy of ice is lower than the internal energy of water at the same temperature. It is super-important to remember that point: freezing water gives off heat. Melting ice absorbs energy—it requires heat to melt. In general, all things being equal, reactions that give off heat and result in a lower internal energy are favored in nature, because in general, things want to go to a lower-energy state. Things are lazy. Making ice gives off heat, so the change in heat favors water turning to ice.

Entropy Pines to Be Free: Entropy is a different story. If you look at entropy as a measure of disorder, increasing entropy increases disorder. A fundamental tenet of thermodynamics is that the entropy of the universe is constantly increasing; hence the universe is constantly becoming more disordered (yay). A better way to define entropy is as a measure of how many different states something can be in. Scientists call these microstates.

Things tend to maximize the number of available microstates and then commence to occupy those microstates in a random way. Things tend to increase in entropy. Things want to be free.

At any given temperature, there are more available positions, speeds, configurations—microstates—in a liquid than in a solid. Water molecules, for instance, are free to spin around and find new neighbors, while ice molecules are locked in a crystal. Being in a solid is more constraining than being in a liquid, so changes in entropy favor ice melting into water.

So Which Wins, Enthalpy or Entropy? It depends on temperature.

Temperature, remember, is a measure of how fast, on average, the