Matter and Energy in Chemistry

States of Matter

All matter in the universe can be classified into one of three states: solid, liquid, or gas. Each state has distinct physical properties that determine its behavior and appearance.

• Solid: Has a definite fixed shape and volume. Particles are arranged in a regular, fixed geometric pattern and move very little, mainly vibrating in place. Solids are not easily compressible.

• Liquid: Has a definite volume but no fixed shape; it takes the shape of its container. Particles move more independently than in solids but are still close together. Liquids are not easily compressible.

• Gas: Has neither a definite shape nor a definite volume. Particles move independently and rapidly, filling the entire volume of their container. Gases are highly compressible.

Key Properties of States of Matter:

• Shape: Fixed (solid), variable (liquid/gas)

• Volume: Fixed (solid/liquid), variable (gas)

• Compressibility: Low (solid/liquid), high (gas)

Physical and Chemical Properties and Changes

Substances can undergo physical or chemical changes. Physical changes do not alter the chemical composition, while chemical changes result in the formation of new substances.

• Physical Property: A characteristic that can be observed or measured without changing the substance's identity (e.g., melting point, color, density).

• Chemical Property: A characteristic that describes a substance's ability to undergo a specific chemical change (e.g., reactivity with water, flammability).

• Physical Change: A change in state or appearance without altering the chemical composition (e.g., melting, boiling).

• Chemical Change: A process in which one or more substances are converted into new substances (e.g., burning, rusting).

Examples:

• Melting ice: Physical change

• Burning coal: Chemical change

• Potassium reacting with water: Chemical change

• Potassium at room temperature: Physical property

• Sodium has a metallic luster: Physical property

Classification of Matter: Pure Substances and Mixtures

Matter can be classified as pure substances or mixtures. Mixtures can be further categorized as homogeneous (uniform composition) or heterogeneous (non-uniform composition).

• Homogeneous Mixture (Solution): Composition is uniform throughout (e.g., air, salt water, champagne).

• Heterogeneous Mixture: Composition is not uniform; different parts can be seen (e.g., salad, hamburger, well-stirred sugar water).

Table: Classification of Substances and Mixtures

Additional info: The above table is inferred from typical examples in GOB Chemistry.

Energy Changes in Physical and Chemical Processes

Energy changes accompany both physical and chemical changes. The main types of energy involved are potential energy (stored energy) and kinetic energy (energy of motion). Energy can also be classified as endothermic (absorbing energy) or exothermic (releasing energy).

• Endothermic Process: Energy is absorbed from the surroundings (e.g., melting ice, evaporation).

• Exothermic Process: Energy is released to the surroundings (e.g., combustion, freezing).

Example: When you make coffee, heating water is an endothermic process because energy is absorbed to increase the water's temperature.

Physical Properties of Compounds and Their Elements

The physical properties of compounds are related to the properties of the elements that make up the compounds. For example, sodium is a soft, metallic element, and sodium compounds often retain some metallic characteristics, such as conductivity.

• Example: Sodium chloride (table salt) is formed from sodium (a metal) and chlorine (a nonmetal). The resulting compound has properties different from its constituent elements.

Summary Table: Physical vs. Chemical Properties and Changes

Key Equations

• Energy Change in Chemical Reactions:

(Endothermic)

(Exothermic)

Additional info: Some context and examples have been inferred to provide a complete study guide for GOB Chemistry students.