Energy Changes in Chemical Reactions

Vocabulary review flashcards covering energy concepts, thermodynamics laws, chemical systems, reaction energetics, and nuclear processes from Unit 3: Energy Changes and Rates of Reaction.

Thermochemistry

The study of energy changes during physical or chemical changes in matter.

Energy

The ability to do work, measured in joules ($\text{J}$).

Work

The energy transferred to an object by a force that causes the object to move, measured in joules ($\text{J}$).

Potential Energy

The form of energy stored due to the position or composition of an object, such as the water held behind a dam or the energy associated with chemical bonds.

Kinetic Energy

The form of energy associated with the motion of an object or entity.

Thermal Energy

The total quantity of potential energy and kinetic energy of a substance, which depends on the speed and number of its entities (atoms, ions, or molecules).

Heat

In science, a verb that refers specifically to the transfer of thermal energy from a warmer object to a colder object.

Temperature

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

First Law of Thermodynamics

The principle stating that energy cannot be created or destroyed; energy is always conserved and can only be converted from one form into another.

Chemical System

The part of the universe composed of the reactants and products being studied.

Surroundings

All the matter in the universe that is not part of the chemical system being studied.

Open System

A chemical system that can exchange both energy and matter with its surroundings, such as an operating propane barbecue.

Closed System

A chemical system that can exchange energy, but not matter, with its surroundings, such as a glow stick.

Isolated System

A theoretical system in which neither matter nor energy can move into or out of the system, which is impossible to set up truly on Earth.

Exothermic Reaction

A chemical reaction that releases energy to the surroundings, meaning the products have lower potential energy ($\Delta E_{\text{p}}$) than the reactants.

Endothermic Reaction

A chemical reaction that absorbs thermal energy from its surroundings, meaning the products have higher potential energy and weaker average bonds than the reactants.

Nuclear Fusion

An exothermic nuclear reaction that occurs when nuclei of small atomic mass combine to form larger, heavier nuclei, such as the process powering stars and the Sun.

Nuclear Fission

An exothermic nuclear reaction in which large, heavy nuclei (typically of elements above atomic number $83$) are split into smaller, lighter nuclei by colliding with a neutron.