heat in physical changes

Thermochemistry

The study of energy changes that accompany physical or chemical changes in matter.

Physical Change

A change affecting the form of a substance but not its chemical composition (e.g., cutting copper, ice melting).

Chemical Change

A change in the chemical composition of a substance that produces something new through chemical reactions (e.g., copper tarnishing).

Energy

The ability to do work. Measured in Joules (J).

Work

The amount of energy transferred by a force over a distance.

Potential Energy

Energy due to the position or composition of an object (e.g., a ball at the top of a hill or a stretched rubber band).

Kinetic Energy

The energy of motion.

Thermal Energy

The total quantity of kinetic and potential energy of all particles in a substance.

Heat

The transfer of thermal energy from a warmer object to a cooler object (e.g., stove transferring energy to boiling water).

Temperature

A measure of the average kinetic energy of the entities (particles) in a substance.

Law of Conservation of Energy (First Law of Thermodynamics)

Energy cannot be created or destroyed; it can only be converted from one form to another during physical or chemical changes.

Chemical System

The specific molecules undergoing a physical change (e.g., melting) or chemical change (e.g., reaction).

Surroundings

All the matter outside of the chemical system (e.g., the beaker, thermometer, surrounding air).

Open System

A system that can exchange both energy and matter with its surroundings (e.g., an open beaker or an operating propane tank).

Closed System

A system that can exchange energy, but NOT matter, with its surroundings (e.g., a sealed glow stick emitting light).

Isolated System

A system that cannot exchange either energy or matter with its surroundings.

Exothermic Change

A process where heat energy is transferred from the system to the surroundings ($\Delta H < 0$). The surroundings warm up while the system cools down (e.g., water freezing).

Endothermic Change

A process where heat energy is absorbed by the system from the surroundings ($\Delta H > 0$). The surroundings cool down while the system warms up (e.g., ice melting).

Phase Changes (Physical Changes)

Physical state transformations: Melting, Freezing, Evaporation, Condensation, Sublimation, Deposition, and Vaporization.

Evaporation vs. Vaporization

Evaporation occurs gradually at the surface of a liquid; Vaporization occurs rapidly throughout the liquid at its boiling point.