Physical and chemical properties Knowledge-Based Study

Study notes

1. What Are Properties of Matter?

   Matter is anything that has mass and takes up space. To identify, describe, and classify different substances, chemists examine their characteristic properties.

   A property is an observable or measurable characteristic of a substance. Properties can be categorized into two major domains:

   • Physical properties: Characteristics that can be observed or measured without altering the chemical identity of the substance.
   • Chemical properties: Characteristics that describe a substance's potential to undergo a change that transforms it into an entirely different chemical substance.

   Understanding Physical Properties

   A physical property can be evaluated without breaking chemical bonds or creating new substances. Measuring a physical property leaves the original chemical composition unchanged.

   Common Examples

   • Color and Odor: Visual and olfactory traits (e.g., sulfur is yellow).
   • State of Matter: Solid, liquid, or gas at room temperature.
   • Melting and Boiling Points: Temperature at which phase transitions occur (e.g., water boils at 100 °C at 1 atm).
   • Density: Mass per unit volume, expressed as $d = \\frac{m}{V}$.
   • Solubility: The ability of a solute to dissolve in a solvent.
   • Electrical and Thermal Conductivity: The ability to conduct heat or electric current (e.g., copper wires conducting electricity).

   Intensive vs. Extensive Properties

   Physical properties are further divided based on sample size:

   • Intensive properties: Independent of the amount of substance present (e.g., density, melting point, color).
   • Extensive properties: Depend directly on the quantity of matter present (e.g., mass, volume, length).

   Understanding Chemical Properties

   A chemical property describes the ability of a substance to combine with or transform into one or more other substances. These properties can only be observed or measured when a substance undergoes a chemical change, resulting in a rearrangement of atoms.

   Common Examples

   • Flammability: The ability of a substance to ignite and burn in the presence of oxygen (e.g., gasoline is highly flammable).
   • Reactivity with Water or Acid: How readily a substance reacts with water or acids (e.g., sodium reacts vigorously with water to form sodium hydroxide and hydrogen gas).
   • Oxidation Potential (Corrosiveness): The tendency to react with oxygen, such as iron rusting to form iron(III) oxide.
   • Toxicity: The degree to which a substance can damage or poison a living organism through chemical interactions.
   • Chemical Stability: The resistance of a substance to decompose under specific environmental conditions.

   How to Tell the Difference

   The definitive test to determine whether a property is physical or chemical lies in what happens to the substance's chemical composition during observation:

   • Does measuring the property alter the identity of the substance? If no, it is a physical property.
   • Does testing the property require the formation of a new chemical substance? If yes, it is a chemical property.

   Comparative Examples

   • Diamond hardness: Hardness is measured by scratch resistance without forming new bonds, so it is a physical property.
   • Diamond combustibility: At high temperatures in pure oxygen, diamond burns to produce carbon dioxide ($\\text{CO}_2$), demonstrating a chemical property.
   • Water boiling: Liquid water turning into steam is a physical change of state ($\\text{H}_2\\text{O}(l) \rightarrow \\text{H}_2\\text{O}(g)$), meaning the boiling point is a physical property.
   • Water electrolysis: Water decomposing into hydrogen and oxygen gases demonstrates the reactivity of water, reflecting a chemical property.