Glossary
Closed System
A system that can exchange energy but not matter with its surroundings.
Example:
A sealed, uninsulated reaction vessel undergoing an exothermic reaction is a closed system; heat can escape, but no chemicals are lost.
Electrostatic Energy
A type of potential energy resulting from the interaction of charged particles. It is governed by Coulomb's Law.
Example:
The strong attraction between a sodium ion (Na+) and a chloride ion (Cl-) in an ionic bond is due to their electrostatic energy.
Endothermic Processes
Processes in which the system absorbs heat from the surroundings, resulting in a positive ΔH value and a decrease in the temperature of the surroundings.
Example:
Melting ice is an endothermic process because the ice absorbs heat from the environment to change from solid to liquid.
Energy
The capacity to do work or transfer heat. It is the fundamental concept underlying all thermodynamic processes.
Example:
When a chemical bond forms, energy is often released, indicating a more stable product.
Enthalpy (H)
The total heat content of a system at constant pressure. It is a state function used to measure heat absorbed or released in chemical processes.
Example:
The enthalpy of a substance includes its internal energy plus the product of its pressure and volume.
Exothermic Processes
Processes in which the system releases heat to the surroundings, resulting in a negative ΔH value and an increase in the temperature of the surroundings.
Example:
The combustion of methane gas is an exothermic process, releasing significant heat and light as it burns.
Isolated System
A system that exchanges neither matter nor energy with its surroundings.
Example:
An ideal calorimeter, perfectly insulated and sealed, aims to be an isolated system to accurately measure heat changes without external interference.
Kinetic Energy
The energy an object possesses due to its motion. In chemistry, it often refers to the motion of particles.
Example:
As water boils, its molecules gain more kinetic energy, causing them to move faster and eventually escape as steam.
Law of Conservation of Energy
Also known as the First Law of Thermodynamics, it states that energy cannot be created or destroyed, only transferred or converted from one form to another.
Example:
In a combustion reaction, the chemical Law of Conservation of Energy dictates that the energy released as heat and light must equal the energy initially stored in the reactants.
Open System
A system that can exchange both matter and energy with its surroundings.
Example:
A beaker of boiling water on a hot plate is an open system because water vapor (matter) escapes and heat (energy) is transferred to the air.
Potential Energy
Stored energy due to an object's position or composition. In chemical systems, this refers to energy stored within chemical bonds.
Example:
A stretched rubber band holds potential energy that is converted into kinetic energy when released.
State Functions
Properties of a system that depend only on its current state, not on the path taken to reach that state. Examples include energy, enthalpy, pressure, volume, and temperature.
Example:
The change in altitude between two points on a mountain is a state function; it doesn't matter if you hiked straight up or took a winding path.
Surroundings
Everything in the universe outside of the defined system with which the system can interact.
Example:
If a chemical reaction occurs in a test tube, the test tube, the air around it, and the lab bench are all part of the surroundings.
System
The specific part of the universe being studied in a thermodynamic analysis, such as the reactants in a chemical reaction.
Example:
When studying the dissolution of a salt in water, the salt and water together constitute the system.
ΔH (Delta H)
The change in enthalpy, representing the amount of heat absorbed or released during a chemical reaction or physical process at constant pressure.
Example:
A negative ΔH value for a reaction indicates that heat is released to the surroundings, making it an exothermic process.