Chemical Alteration in Matter
Chemical changes in matter are permanent and cannot be reversed. For example, an ice cube melts into water but cannot return to being an ice cube again.
The tuff closest to the intrusion shows extensive phyllic alteration to muscovite and illite, with interlocking quartz. SWIR and XRD analysis indicate this rock also contains chlorite and carbonate.
Dissolution
Dissolution is a chemical process in which a solid or other substance dissolves into a liquid. The process is endothermic, which means that it releases energy as it dissolves. Its energy is primarily drawn from the intermolecular attractive forces between like molecules in solvent and solute.
In addition, the physical structure of the dissolving material changes. For example, if the object is a solid, its shape becomes irregular. This occurs because molecules in the solvent interact with all parts of its surface, changing its physical characteristics.
In the pharmaceutical industry, dissolution is used to test the quality of a drug formulation or manufacturing process. It is a key step in establishing a link between the drug and its biological activity. It is also a vital tool in identifying batch-to-batch consistency and compliance with specifications. Dissolution models are often based on simple diffusion equations or correlations. These models have limitations, however. A more advanced model would consider distributions of particles and the fragmentation that occurs at a particle surface.
Oxidation
Oxidation is a reaction that occurs when substances, especially metals, come into contact with oxygen molecules. This can also occur in living tissues, and it is one of the most common chemical alteration reactions in nature. The process of oxidation changes the chemical properties of the substances involved by breaking and forming certain chemical bonds. This can change the physical properties of the substance, such as its temperature.
The exact chemical reactions involved in oxidation are called redox reactions. This is because they involve the transfer of electrons between reactants and products. The oxidation of a compound is characterized by a net loss of electrons from the reactant, while reduction involves a net gain of electrons from the product. A balance of oxidation and reduction reactions is required in order to form the stable compounds found in nature. The reaction of microbial respiration, for example, is the result of an oxidation-reduction reaction that generates reducing conditions in soils and groundwater.
Cementation
Cementation is a process that changes sediments into rock. It involves mineral crystals sticking the individual grains of sediment together, much like cement sticks sand particles together in a bricklayer’s mortar. This is a major step in the process of turning sediment into rock, which is called lithification or diagenesis.
The most common cementing minerals are calcite and silica. When water containing these minerals passes through a sandstone, it fills the pore spaces between the original sediment grains and precipitates new crystalline material that bonds the grains of sediment together. This cementation makes sandstone into rock and gravel into conglomerate or breccia.
The process of cementation also destroys some of the primary porosity in the reservoir. The resulting porosity is often reduced to less than 6%, which can severely inhibit hydrocarbon migration. This loss of primary porosity is referred to as late cementation and is associated with a variety of formations, including sparry calcite, dolomite, authigenic kaolinite, illite, and iron-rich chlorite.
Precipitation
A precipitation reaction is a chemical reaction that causes an insoluble compound to form. It can be caused by reacting two salts or by changing the temperature to affect the solubility of a compound. The resulting insoluble compound is known as the precipitate. Precipitation reactions serve many useful purposes, including purification and separating metals.
In meteorology, precipitation is the phenomenon of water vapor condensing in clouds and falling down as liquid (rain) or solids (snow). This happens when a region’s atmosphere becomes saturated with water molecules, which then fall out of the air under gravity as rain, snow, sleet or hail.
The chemical process of precipitation is used to separate ionic metals from industrial process wastewaters and to make pigments. Chemical precipitation involves mixing a solution containing the ionic compound you want to precipitate with a reagent that can cause that reaction. The mixture of silver nitrate and sodium chloride in water, for example, produces the solid substance known as silver chloride.
