Biogas is a mixture of different gases produced by anaerobic decomposition (with methanogen or anaerobic organisms), or fermentation, of biomass – organic material (including animal dung, human sewage, food waste, crop residues, and industrial and municipal wastes). Biogas is a renewable energy source. It is composed primarily of methane (up to 60%), which is the combustible component, carbon dioxide, and […]


Perovskite (discovered in the Ural Mountains of Russia by Gustav Rose in 1839 and is named after Russian mineralogist Lev Perovski 1792–1856) is a calcium titanium oxide mineral composed of calcium titanate (CaTiO3). Its name is also applied to the class of compounds which have the same type of crystal structure as CaTiO3 \((^{\textrm{XII}}\textrm{A}^{2+\textrm{VI}}\textrm{B}^{4+}\textrm{X}^{2-}_3)\), known as the perovskite structure, which includes many synthetic perovskites: many of […]

Chemical reaction

A chemical reaction is a transformation of matter that occurs without measurable variations in mass, in which one or more chemical species (called reactants or reagents) modify their structure and original composition to generate other chemical species (called products). Chemical reactions, in which chemical bonds are broken and formed, require an initial investment of energy. Kinetic energy, […]


Cohesion (or cohesive attraction, or cohesive force) is the tendency of different parts of a substance to hold together (being mutually attractive). Cohesion is due to forces acting between its molecules: a molecule will repel one close to it but attract one that is farther away. This situation results in both cohesion and adhesion. The attractive […]


In chemistry, a suspension is defined as a heterogeneous mixture in which particle size of one or more components is greater than 1000 nm. When mud is dissolved in water and stirred vigorously, particles of mud are distributed evenly in water. After some time, the particles of this solution settle underwater due to the influence of gravity. […]


Chemistry (from kemà, the book of Egyptian art secrets, from the Arabic word al-kīmīā, الكيمياء) is the science that studies the composition of matter and its behavior based on this composition, also called “central science” because it connects other natural sciences, such as astronomy, physics, materials sciences, biology, and geology.

Van der Waals equation

The van der Waals equation (or van der Waals equation of state; named after Johannes Diderik van der Waals) is an equation of state that generalizes the ideal gas law based on plausible reasons that real gases do not act ideally. \[\left(P+a\dfrac{1}{V_m^2}\right)(V_m-b)=RT\] where \(a\) is a constant whose value depends on the gas, \(b\) is the volume […]

Functional groups

Functional groups are groups of atoms that occur within molecules and confer specific chemical properties to those molecules. We find them along the “carbon backbone” of macromolecules. Chains and/or rings of carbon atoms with the occasional substitution of an element such as nitrogen or oxygen form this carbon backbone. Molecules with other elements in their carbon […]


Homogeneous mixture. Heterogeneous mixture.