substance

(noun)

A form of matter that has constant chemical composition and characteristic properties. It is composed of one type of atom or molecule.

Related Terms

Examples of substance in the following topics:

  • Substance Abuse and Health

    • Substance abuse, or the habitual, harmful use of drugs, can have detrimental effects on the mind and body.
    • Individuals who use substances to the point of dependence are at even greater risk for physical health problems, or even overdose, due to development of tolerance, or needing to use more and more of the substance to obtain the desired effect.
    • Substance abuse can have a variety of detrimental effects on the mind and body of the user.
    • Some people turn to substances to self-medicate for disorders like depression, anxiety, or bipolar disorder, only to find that substance use, while diminishing psychological distress in the short-term, only exacerbates the symptoms in the long run. 
    • Substance abuse can also lead to secondary physical effects.

  • Substances and Mixtures

    • Substances are composed of pure elements or chemically bonded elements, whereas mixtures are composed of non-bonded substances.
    • All compounds are substances, but not all substances are compounds.
    • Simple or seemingly pure substances found in nature can in fact be mixtures of chemical substances.
    • A mixture refers to the physical combination of two or more substances in which the identities of the individual substances are retained.
    • Introduction to classifying matter as a substance or a mixture of substances.

  • Substance-Related and Addictive Disorders

    • Substance use disorder combines the previous DSM-IV-TR categories of "substance abuse" and "substance dependence" into a single disorder, measured on a diagnostic continuum from mild to severe.
    • Physiological dependence occurs when the body has to adjust to the substance by incorporating the substance into its 'normal' functioning.
    • Substance-related disorders, a category which includes both substance dependence and substance abuse, can lead to significant personal, interpersonal, and societal problems.
    • Genetic factors may create a predisposition for substance abuse, which means that an individual may have a tendency toward substance abuse.
    • Individuals suffering from substance use disorder and addiction may engage in the use of many substances.

  • Specific Heat

    • Experiments show that the transferred heat depends on three factors: (1) The change in temperature, (2) the mass of the system, and (3) the substance and phase of the substance .
    • where ϱ is the density of the substance and V is its volume.
    • The table below lists representative values of specific heat for various substances.
    • Listed are the specific heats of various substances.
    • (c) The amount of heat transferred depends on the substance and its phase.

  • The Role of Passive Transport

    • Plasma membranes must allow or prevent certain substances from entering or leaving a cell.
    • In passive transport, substances move from an area of higher concentration to an area of lower concentration .
    • Substances diffuse from areas of high concentration to areas of lower concentration; this process continues until the substance is evenly distributed in a system.
    • In solutions containing more than one substance, each type of molecule diffuses according to its own concentration gradient, independent of the diffusion of other substances.
    • In living systems, diffusion of substances in and out of cells is mediated by the plasma membrane.

  • Characteristics of Connective Tissue

    • CT has three main components: a) ground substance, b) fibers and c) cells.
    • Together the ground substance and fibers make up the extracellular matrix.
    • Ground substance is a clear, colorless, viscous fluid that fills the space between the cells and fibers.
    • The ground substance functions as a molecular sieve for substances to travel between blood capillaries and cells.
    • Connective tissues consist of three parts: cells suspended in a ground substance or matrix; and most have fibers running through it.

  • Renal Clearance

    • Each substance has its own specific clearance that depends on its unique filtration characteristics.
    • Clearance can be either a constant or variable component over time, depending on the type of substance.
    • If any of those variables change, the renal clearance rate of a substance will change as well.
    • Additionally, the characteristics of the substance of interest will also determine some components of clearance.
    • It is also important to note that renal clearance is not the only form of clearance that occurs for the substances within the plasma of the body.

  • Molar Mass of Compounds

    • The molar mass of a particular substance is the mass of one mole of that substance.
    • Even the smallest quantity of a substance will contain billions of atoms, so chemists generally use the mole as the unit for the amount of substance.
    • In other words, a mole is the amount of substance that contains as many entities (atoms, or other particles) as there are atoms in 12 grams of pure carbon-12.
    • Each ion, or atom, has a particular mass; similarly, each mole of a given pure substance also has a definite mass.
    • Molar mass is the mass of a given substance divided by the amount of that substance, measured in g/mol.

  • Physical and Chemical Changes to Matter

    • Another way to think about this is that a physical change does not cause a substance to become a fundamentally different substance but a chemical change causes a substance to change into something chemically new.
    • For example, mixing salt and pepper creates a new substance without changing the chemical makeup of either component.
    • Phase changes are changes that occur when substances are melted, frozen, boiled, condensed, sublimated, or deposited.
    • They are also physical changes because they do not change the nature of the substance.
    • A chemical change might also result in the formation of a precipitate, such as the appearance of a cloudy material when dissolved substances are mixed.

  • Substances that Exist as Gases

    • Substances that exist in the gas phase exhibit negligible intermolecular forces.
    • Near absolute zero, a substance exists as a solid.
    • The temperature of a substance is a measure of the average kinetic energy of the particles.
    • Under standard conditions (1 atm, 273 K), a substance which exists as a gas is called a pure gas and (disregarding any substance-specific intermolecular forces or particle volume that could alter this value) has a volume of 22.4 L per mole.
    • At STP, if the boiling point of a given substance is below 273 K then you would expect that substance to be in gas form.