Every sample of matter is characterized by a set of qualities called properties. These properties act as the identifying characteristics that distinguish one substance from another. Understanding these inherent qualities is fundamental to chemistry because they dictate how a substance will behave in the environment. By examining these traits, we can predict a substance’s potential for transformation, which is the core of chemical study.
Understanding Chemical Properties Versus Physical Properties
A chemical property is a characteristic that can only be observed or measured when the substance undergoes a change in its fundamental chemical identity. Confirming a chemical property requires performing a chemical reaction, which results in the formation of an entirely new substance with a different composition and structure. For example, determining if a metal is reactive with acid requires mixing them, causing the metal to dissolve and hydrogen gas to be released.
This differs from a physical property, which can be observed or measured without altering the substance’s chemical composition. Physical properties include traits like color, density, and melting point. When ice melts into liquid water, its physical state changes, but its chemical identity remains H2O.
Examples of Dynamic Chemical Reactivity
Dynamic chemical properties describe a substance’s tendency to actively interact and change when placed in contact with other specific substances.
Flammability
The ability of a material to burn, known as flammability or combustibility, describes the potential for a rapid, high-temperature reaction with an oxidant, typically oxygen. During this process, the chemical bonds of the fuel break and new bonds form in the products, releasing energy as heat and light.
Reactivity
Reactivity with specific chemical classes, such as water, acids, or bases, defines a substance’s behavior. Highly reactive elements, like the alkali metals, react violently with water, displacing hydrogen and forming a hydroxide solution. This reactivity is important for handling and storage, as even trace amounts of moisture can initiate a chemical change.
Oxidation Potential
A substance’s oxidation potential describes its readiness to lose electrons, which is the basis for processes like corrosion and tarnishing. Iron’s tendency to rust is a chemical property resulting from the slow reaction between the metal, oxygen, and water to form iron oxide.
Examples of Inherent Chemical States
Inherent chemical properties relate to a substance’s internal stability and its specific chemical environment.
Chemical Stability
Chemical stability measures a compound’s resistance to decomposition or breaking down into simpler substances under normal environmental conditions. Highly stable compounds, such as noble gases, show a low propensity for chemical change. Conversely, a substance like an explosive has very low stability and a high potential for rapid decomposition.
Toxicity
Toxicity is considered a chemical property because it involves the substance chemically interfering with biological processes within an organism, often by reacting with cell components. The degree of toxicity is an inherent characteristic, determined by the molecular structure.
pH Level
The pH level quantitatively indicates a substance’s acidity or basicity by measuring the concentration of hydrogen ions in a solution. This pH value determines how the substance will react with other materials, such as dissolving metals or neutralizing other compounds.
Heat of Formation and Combustion
The heat of formation and heat of combustion are quantitative chemical properties related to a molecule’s energy state. Heat of formation measures the energy absorbed or released when a compound is formed from its constituent elements, providing insight into its energetic stability. Heat of combustion measures the energy released when a substance is completely burned.