What is a spontaneous process? Provide an example.

In the world of chemistry and physics, 'free energy' refers to the energy that is available in a system to do work. It's a thermodynamic concept that explains whether a process will occur spontaneously or not. Free energy combines the internal energy of a system with its entropy, a measure of disorder, to predict the natural direction of a process.

The most recognized forms are the Gibbs free energy (\(G\)) for reactions at a constant pressure and the Helmholtz free energy (\(A\)) for reactions at a constant volume. The change in free energy, denoted as \(\Delta G\), tells us which processes are possible. If \(\Delta G\) is negative, we're in the zone of spontaneous reactions; the process can theoretically proceed without external energy. If \(\Delta G\) is positive, additional energy is required to make the reaction happen.

An example that shows \(\Delta G\) in action is a battery powering a device. Inside the battery, a chemical reaction occurs that has a negative \(\Delta G\), releasing energy to power the device. The battery continues to provide power until the free energy has been depleted, signifying that the spontaneous reaction has reached completion.

Reactions that are classified as energetically favorable are those which release energy during the process. This release can be in the form of heat (exothermic reactions) or increasing disorder (increasing entropy) within the system. These reactions occur naturally and do not require an input of energy to proceed; in other words, they are spontaneous.

A telling sign of energetically favorable reactions is a negative change in free energy \(\Delta G\). This concept is invaluable for predicting the course of chemical reactions. For instance, when a piece of wood combusts, it does so spontaneously in the presence of oxygen, releasing heat and light. In living organisms, the breakdown of glucose during cellular respiration is an energetically favorable process that releases energy for the cell's use.

Energetically favorable reactions are essential in both industrial applications and biological systems, as they underpin the production of energy and the synthesis of complex molecules from simpler ones. These reactions drive the functionality of engines, power plants, and even our own metabolism.

Phase transitions are transformations between different states of matter—like solids, liquids, and gases. These transitions often occur spontaneously and are prime examples of such processes in nature. During a phase transition, a substance changes its physical structure and properties, but not its chemical composition.

Common phase transitions include melting (solid to liquid), freezing (liquid to solid), vaporization (liquid to gas), and condensation (gas to liquid). Each of these transitions occurs at a specific temperature and pressure, known as the substance’s melting point, freezing point, boiling point, and condensation point, respectively.

When ice melts into water at room temperature, it absorbs heat from the environment. This absorption increases the disorder within the system, which is a key factor leading to a negative change in free energy, allowing the spontaneous melting to occur. This type of transition exemplifies how a substance can undergo a physical change while remaining energetically favorable and not requiring an energy input from the external environment.