Chapter 3: Matter and Energy – Study Notes for Introductory Chemistry

Matter and Its Composition

Defining Matter

Matter is the fundamental concept in chemistry, referring to anything that occupies space and has mass. All physical objects, from visible items like steel and water to invisible substances like air, are forms of matter.

• Matter: Anything that has mass and takes up space.

• Some matter is visible (e.g., wood, plastic), while other types (e.g., air, microscopic dust) require magnification to observe.

Atoms and Molecules

At the microscopic level, matter is composed of atoms and molecules. These are the smallest units that retain the properties of an element or compound.

• Atom: The smallest unit of an element, consisting of protons, neutrons, and electrons.

• Molecule: Two or more atoms bonded together in specific geometric arrangements.

• Advances in microscopy allow us to visualize atoms and molecules.

• Example: Water molecules (H2O) and carbon atoms in graphite.

States of Matter

Common States: Solid, Liquid, Gas

Matter exists in three primary states, each with distinct physical properties based on the arrangement and movement of atoms or molecules.

• Solid: Atoms/molecules are closely packed in fixed positions. Solids have a definite shape and volume.

• Liquid: Atoms/molecules are close but can move past each other. Liquids have a definite volume but take the shape of their container.

• Gas: Atoms/molecules are far apart and move freely. Gases have neither definite shape nor volume and are compressible.

Types of Solids

• Crystalline Solid: Atoms/molecules are arranged in a well-ordered, repeating pattern (e.g., salt, diamond).

• Amorphous Solid: Atoms/molecules lack long-range order (e.g., glass, rubber, plastic).

Table: Properties of Solids, Liquids, and Gases

State	Atomic/Molecular Motion	Spacing	Volume	Shape	Compressibility
Solid	Oscillation/vibration about fixed point	Close together	Definite	Definite	Incompressible
Liquid	Free to move relative to one another	Close together	Definite	Indefinite	Incompressible
Gas	Free to move relative to one another	Far apart	Indefinite	Indefinite	Compressible

Classification of Matter

Pure Substances and Mixtures

Matter can be classified based on its composition:

• Pure Substance: Composed of only one type of atom or molecule.

• Mixture: Composed of two or more different substances physically combined in variable proportions.

Elements and Compounds

• Element: A pure substance that cannot be broken down into simpler substances by chemical means. The smallest unit is an atom. (e.g., helium, gold)

• Compound: A pure substance composed of two or more elements chemically combined in fixed, definite proportions. (e.g., water, H2O)

Types of Mixtures

• Homogeneous Mixture: Uniform composition throughout (e.g., air, saltwater, sweetened tea).

• Heterogeneous Mixture: Composition varies from one region to another (e.g., oil and water, noodle soup).

Table: Classification of Matter

Type	Description	Examples
Element	Pure substance, cannot be decomposed	Helium, gold
Compound	Pure substance, composed of two or more elements in fixed proportions	Water (H2O), carbon dioxide (CO2)
Homogeneous Mixture	Uniform composition	Air, saltwater
Heterogeneous Mixture	Variable composition	Salad dressing, noodle soup

Properties and Changes in Matter

Physical vs Chemical Properties

• Physical Property: Can be observed without changing the substance's composition (e.g., odor, boiling point, color, density).

• Chemical Property: Can only be observed by changing the substance's composition (e.g., flammability, reactivity, acidity).

Physical vs Chemical Changes

• Physical Change: Alters appearance but not composition (e.g., melting, boiling, cutting).

• Chemical Change: Alters composition, resulting in new substances (e.g., rusting, burning).

Phase changes (melting, freezing, vaporization, condensation, sublimation, deposition) are always physical changes.

Conservation Laws

Law of Conservation of Mass

In any physical or chemical change, the total mass of the substances involved remains constant.

• Law of Conservation of Mass: Matter is neither created nor destroyed in a chemical reaction.

• Example: Burning butane – the mass of reactants equals the mass of products.

Energy in Chemistry

Definition and Forms of Energy

• Energy: The capacity to do work.

• Kinetic Energy: Energy of motion.

• Potential Energy: Energy due to position or composition.

• Thermal Energy: Energy associated with the random motion of atoms and molecules.

• Chemical Energy: A form of potential energy stored in chemical bonds.

Law of Conservation of Energy

• Energy cannot be created or destroyed; it can only change forms or be transferred.

Units of Energy

• Joule (J): SI unit of energy.

• Calorie (cal): Energy required to raise 1 g of water by 1°C. $1\ \text{cal} = 4.184\ \text{J}$

• Calorie (Cal): Nutritional calorie, $1\ \text{Cal} = 1000\ \text{cal}$

• Kilowatt-hour (kWh): $1\ \text{kWh} = 3.60 \times 10^6\ \text{J}$

Exothermic and Endothermic Processes

• Exothermic Reaction: Releases energy to the surroundings (e.g., burning wood).

• Endothermic Reaction: Absorbs energy from the surroundings (e.g., melting ice).

Temperature and Heat

Temperature Scales

• Fahrenheit (°F): Water freezes at 32°F, boils at 212°F.

• Celsius (°C): Water freezes at 0°C, boils at 100°C.

• Kelvin (K): Absolute zero is 0 K; water freezes at 273 K, boils at 373 K.

Temperature Conversion Formulas

• $K = ^\circ C + 273.15$

• $^\circ C = \frac{^\circ F - 32}{1.8}$

Heat and Specific Heat Capacity

• Heat: Transfer of thermal energy due to temperature difference (measured in J or cal).

• Specific Heat Capacity (C): Amount of heat required to raise the temperature of 1 g of a substance by 1°C (units: J/g°C).

• Water has a high specific heat capacity ($4.184\ \text{J/g}^\circ\text{C}$), making it effective for cooling.

Table: Specific Heat Capacities of Some Common Substances

Substance	Specific Heat Capacity (J/g°C)
Lead	0.128
Gold	0.128
Silver	0.235
Copper	0.385
Iron	0.449
Aluminum	0.903
Ethanol	2.42
Water	4.184

Calculating Heat Transfer

• The relationship between heat, mass, specific heat capacity, and temperature change is given by:

$q = m \times C \times \Delta T$

• Where q is heat (J), m is mass (g), C is specific heat capacity (J/g°C), and $\Delta T$ is the temperature change ($T_{final} - T_{initial}$).

Summary Table: Key Concepts

Concept	Description
Matter	Anything with mass and volume; exists as solid, liquid, or gas
Pure Substance	Element or compound with fixed composition
Mixture	Physical combination of substances; can be homogeneous or heterogeneous
Physical Property	Observed without changing composition (e.g., color, melting point)
Chemical Property	Observed by changing composition (e.g., flammability)
Physical Change	Change in appearance, not composition (e.g., melting)
Chemical Change	Change in composition, new substances formed (e.g., rusting)
Conservation of Mass	Mass is conserved in chemical reactions
Conservation of Energy	Energy is conserved; can change forms
Specific Heat Capacity	Heat required to raise 1 g of substance by 1°C

Additional info: Some explanations and examples have been expanded for clarity and completeness, following standard introductory chemistry textbooks.