Properties of Substances – Notes
What are Properties?
Characteristics and behaviors used to describe matter.
Two main types: Physical and Chemical.
Physical Properties
Can be observed or measured without changing the identity of the substance.
Examples:
Mass: amount of matter; measured in kg. Formula: (M = F / a).
Density: mass ÷ volume; varies with temperature and pressure.
Volume: space an object occupies.
Boiling point: liquid → gas.
Melting point: solid → liquid.
Conductivity: ability to conduct electricity.
Heat capacity: heat required to change temperature of a mass by 1 K (J/K).
Malleability: ability to be hammered into sheets.
Ductility: ability to be drawn into wires.
Other examples: thermal conductivity, solubility, state of matter, luster, color, texture.
Extensive properties: depend on amount of matter (mass, volume).
Intensive properties: independent of amount (color, density, boiling point).
Chemical Properties
Describe how a substance can change into a new substance.
Evident during chemical reactions.
Examples:
Reactivity (with oxygen, air, water).
Flammability.
Toxicity.
Oxidation states.
Heat of combustion.
Chemical stability.
Enthalpy of formation.
Physical vs Chemical Changes
Physical change: alters form but not composition (e.g., freezing water, cutting hair, bending paper clip).
Chemical change: produces new substances (e.g., souring milk, rusting iron, burning wood, vinegar + baking soda reaction).
Signs of Chemical Change
Change in temperature:
Exothermic: releases energy (rusting).
Endothermic: absorbs energy (antacid + water).
Production of odor (rotting eggs, lightning reaction with oxygen).
Change in color (fruit ripening, rust).
Formation of bubbles (vinegar + baking soda).
Formation of a solid/precipitate (clam shells from seawater).
Comparing Physical and Chemical Properties
Helium: physical – less dense than air; chemical – nonflammable.
Wood: physical – grainy texture; chemical – flammable.
Baking soda: physical – white powder; chemical – reacts with vinegar.
Powdered sugar: physical – white powder; chemical – does not react with vinegar.
Rubbing alcohol: physical – clear liquid; chemical – flammable.
Red food coloring: physical – red color; chemical – reacts with bleach.
Iron/Tin: physical – malleable; chemical – reacts with oxygen.
Energy Basics
Energy: ability to do work or cause change.
Kinetic energy: energy of motion.
High kinetic energy → particles move fast and far apart.
Low kinetic energy → particles move slow and close together.
Thermal energy: total kinetic energy of all particles in a sample.
Temperature: average kinetic energy of particles.
Heat: transfer of thermal energy from high temp → low temp.
States of Matter
Solid: definite shape & volume; particles close together, vibrate in place.
Liquid: definite volume, no definite shape; particles further apart, slide past each other.
Gas: no definite shape or volume; particles move very fast, most kinetic energy.
Changes of State
Occur when thermal energy is absorbed or released.
Melting: solid → liquid (absorbs energy).
Freezing: liquid → solid (releases energy).
Boiling/Vaporization: liquid → gas at boiling point (absorbs energy).
Evaporation: liquid → gas below boiling point (absorbs energy).
Condensation: gas → liquid (releases energy).
Sublimation: solid → gas directly (absorbs energy).
Deposition: gas → solid directly (releases energy).
Chemical Reactions
Transform one or more substances into different substances.
Different from state changes (which keep the same substance, just different form).
Types of chemical reactions:
Synthesis
Decomposition
Single replacement
Double replacement
Combustion
Categories:
Endothermic: absorb energy/heat.
Exothermic: release energy/heat.
Result from electron interactions: breaking/forming chemical bonds.
Reaction rates depend on:
Type of reagents
Concentration of reagents/substrate
Temperature
Pressure
Higher temperature generally increases reaction rate (weakens bonds, speeds collisions).