Glossary
Atomic Mass Unit (u)
A standard unit of mass used to express atomic and molecular masses, approximately equal to 1/12th the mass of a carbon-12 atom. It is commonly used in nuclear physics calculations.
Example:
The mass of a proton is approximately 1.007 Atomic Mass Unit (u).
Change in Mass (Δm) / Mass Defect
The difference between the total mass of the reactants and the total mass of the products in a nuclear reaction. This 'missing' mass is converted into energy according to E=Δmc².
Example:
When a heavy nucleus undergoes fission, the slight Change in Mass (Δm) between the original nucleus and its fragments accounts for the enormous energy released.
Disintegration Energy (Q)
The net energy released or absorbed during a nuclear reaction, calculated from the difference in mass between reactants and products. A positive Q indicates energy release, while a negative Q indicates energy absorption.
Example:
In a nuclear fusion reactor, scientists aim for reactions with a high positive Disintegration Energy (Q) to generate substantial power.
E = Δmc²
Einstein's famous equation quantifying the relationship between energy (E) and the change in mass (Δm), where 'c' is the speed of light squared. It shows that a small mass change yields a large energy change.
Example:
When calculating the energy released by a nuclear bomb, physicists use E = Δmc² to determine how much energy is produced from the tiny fraction of mass that is converted.
Endothermic Reaction
A nuclear or chemical reaction that absorbs energy, typically as heat, from its surroundings. The products of an endothermic reaction have more energy than the reactants.
Example:
An instant cold pack uses an Endothermic Reaction to absorb heat from your skin, making the pack feel cold.
Exothermic Reaction
A nuclear or chemical reaction that releases energy, typically as heat, into its surroundings. The products of an exothermic reaction have less energy than the reactants.
Example:
The burning of wood is an Exothermic Reaction because it releases heat and light, warming the surrounding air.
Heat of Reaction
The total amount of heat absorbed or released during a chemical or nuclear reaction. It is a measure of the energy difference between reactants and products.
Example:
Measuring the Heat of Reaction for a new fuel source helps engineers determine its efficiency and energy output.
Mass-Energy Equivalence
A fundamental principle stating that mass and energy are interchangeable and can be converted into one another. This concept is central to understanding nuclear reactions.
Example:
The immense power of the sun comes from nuclear fusion, where a tiny amount of mass is converted into a colossal amount of energy, demonstrating Mass-Energy Equivalence.
Mega-electron Volts (MeV)
A unit of energy commonly used in nuclear and particle physics, equal to one million electron volts. It is a convenient unit for expressing the large energy changes in nuclear reactions.
Example:
The energy released in a typical nuclear fusion reaction is often on the order of several Mega-electron Volts (MeV).
Products
The new substances or particles formed as a result of a chemical or nuclear reaction. They are the output of the transformation.
Example:
When hydrogen and oxygen combine in a fuel cell, water is the primary Product generated.
Reactants
The initial substances or particles that undergo a transformation in a chemical or nuclear reaction. They are consumed during the process.
Example:
In the process of photosynthesis, carbon dioxide and water are the Reactants that sunlight converts into glucose and oxygen.
Speed of Light (c)
A fundamental physical constant representing the speed at which light and all other electromagnetic waves travel in a vacuum, approximately 3 x 10^8 m/s. Its squared value in E=mc² highlights the immense energy contained in mass.
Example:
The Speed of Light (c) is so fast that a beam of light can travel around the Earth seven and a half times in one second.
Spontaneous Reaction
A reaction that occurs without continuous external energy input once initiated, typically because it releases energy (has a positive Q value).
Example:
Radioactive decay is a Spontaneous Reaction because unstable nuclei naturally transform into more stable forms, releasing energy in the process.