Glossary
Absolute Zero
The theoretical temperature at which all molecular motion ceases and a system has its minimum possible energy and zero entropy (0 Kelvin or -273.15°C).
Example:
Scientists use specialized equipment to cool substances to temperatures approaching absolute zero to study quantum phenomena, where particles exhibit minimal thermal motion.
Enthalpy (H)
A thermodynamic property representing the total heat content of a system at constant pressure.
Example:
The enthalpy change (ΔH) for an exothermic reaction, like the combustion of methane, is negative because heat is released to the surroundings.
Entropy (S)
A measure of the disorder or randomness of a system, reflecting the number of possible microscopic arrangements of particles.
Example:
When a solid sugar cube dissolves in water, its entropy increases as the ordered solid becomes disordered ions in solution.
First Law of Thermodynamics
States that energy cannot be created or destroyed in an isolated system; it can only be transferred or changed from one form to another.
Example:
When a plant converts sunlight into chemical energy through photosynthesis, it demonstrates the First Law of Thermodynamics by transforming energy, not creating or destroying it.
Gases
A state of matter where particles are widely separated and move randomly, resulting in an indefinite shape and volume and the highest entropy.
Example:
The air inside a balloon consists of gases, whose molecules move freely and randomly, exhibiting the highest degree of disorder.
Gibbs Free Energy (G)
A thermodynamic potential that measures the 'useful' or process-initiating work obtainable from an isothermal, isobaric thermodynamic system, determining the spontaneity of a process.
Example:
A negative change in Gibbs Free Energy (ΔG) for a reaction indicates that it will proceed spontaneously under constant temperature and pressure.
Liquids
A state of matter where particles are close together but can move past one another, giving it a definite volume but an indefinite shape and medium entropy.
Example:
Water at room temperature is a liquid, its molecules having more freedom to move and tumble than in ice, leading to higher entropy.
Second Law of Thermodynamics
States that for any spontaneous process, the total entropy of the universe (system + surroundings) must increase or remain constant.
Example:
A dropped glass shattering into pieces is a classic illustration of the Second Law of Thermodynamics, as the disorder of the system increases spontaneously.
Solids
A state of matter characterized by tightly packed particles in fixed positions, resulting in a definite shape and volume and the lowest entropy.
Example:
The highly ordered crystal lattice of a diamond exemplifies a solid, where atoms have minimal movement and thus low entropy.
Spontaneity
The tendency of a process to occur without continuous external intervention once initiated.
Example:
Rusting of iron is a spontaneous process, as it occurs naturally over time without needing constant energy input.
Thermochemistry
The branch of chemistry that studies the heat changes associated with chemical reactions and physical transformations.
Example:
When you burn a candle, thermochemistry helps explain the heat and light produced from the chemical reaction.
Third Law of Thermodynamics
States that the entropy of a perfect crystalline substance at absolute zero (0 Kelvin) is zero.
Example:
Cooling a perfectly ordered crystal of silicon to near absolute zero would theoretically result in its entropy approaching zero, as described by the Third Law of Thermodynamics.