Glossary
Dissolution
The process by which a solute dissolves in a solvent to form a solution, involving changes in both enthalpy and entropy.
Example:
The dissolution of salt in water involves breaking ionic bonds and forming ion-dipole interactions.
Endothermic
A process or reaction that absorbs heat from its surroundings, resulting in a positive change in enthalpy (ΔH > 0).
Example:
Melting ice is an endothermic process because it absorbs heat from the surroundings to change phase.
Energy transfer
The movement of energy from one system or substance to another, often in the form of heat or work.
Example:
When a hot metal is placed in cold water, energy transfer occurs as heat moves from the metal to the water.
Enthalpy (ΔH)
A thermodynamic property representing the total heat content of a system; the change in enthalpy (ΔH) indicates the heat absorbed or released during a constant-pressure process.
Example:
The combustion of methane has a negative ΔH, indicating it's an exothermic reaction that releases heat.
Entropy (ΔS)
A thermodynamic property that measures the disorder or randomness of a system; a positive change in entropy (ΔS > 0) indicates increased disorder.
Example:
When a solid sugar cube dissolves in water, its molecules spread out, leading to an increase in entropy.
Equilibrium constant (K)
A value that expresses the ratio of products to reactants at equilibrium, indicating the extent to which a reaction proceeds; a spontaneous reaction has K > 1.
Example:
For the Haber process, a large equilibrium constant indicates that product formation (ammonia) is highly favored at equilibrium.
Exothermic
A process or reaction that releases heat to its surroundings, resulting in a negative change in enthalpy (ΔH < 0).
Example:
Burning wood is an exothermic process, as it releases heat and light into the environment.
Gibbs Free Energy (ΔG)
A thermodynamic potential that measures the maximum reversible work that may be performed by a thermodynamic system at a constant temperature and pressure; it predicts the spontaneity of a process.
Example:
A reaction with a negative ΔG will proceed spontaneously under the given conditions, like iron rusting in moist air.
Nonspontaneous reaction
A reaction or process that requires continuous external energy input to proceed under a given set of conditions, characterized by a positive change in Gibbs Free Energy (ΔG > 0).
Example:
The synthesis of ozone from oxygen is a nonspontaneous reaction that requires energy from lightning or UV radiation.
Phase changes
Transitions of matter from one state (solid, liquid, gas) to another, which are often accompanied by significant changes in entropy.
Example:
The phase change from liquid water to steam involves a large increase in entropy due to the greater freedom of gas molecules.
Spontaneous reaction
A reaction or process that occurs without continuous external energy input under a given set of conditions, characterized by a negative change in Gibbs Free Energy (ΔG < 0).
Example:
The combustion of gasoline is a spontaneous reaction once initiated, releasing energy to power an engine.
Thermodynamics
The branch of chemistry that studies energy transfer and transformations during chemical reactions and physical processes.
Example:
Understanding thermodynamics helps predict if a chemical reaction will release heat or require energy input.