Chapter 3: Matter and Energy

3.1 Classification of Matter

Matter is the material that makes up all things, defined as anything that has mass and occupies space. Understanding the classification of matter is fundamental in chemistry, as it helps distinguish between different types of substances and their properties.

• Pure Substances: Have a fixed or definite composition. They are further classified as:

  • Elements: Composed of one type of atom (e.g., copper, lead, aluminum).

  • Compounds: Composed of two or more elements combined in a definite ratio (e.g., water, table salt).

• Mixtures: Contain two or more substances physically mixed but not chemically combined. They can be separated by physical methods and exist in varying proportions.

  • Homogeneous Mixtures: Uniform composition throughout; different parts are not visible (e.g., brass, air, nitrox for scuba tanks).

  • Heterogeneous Mixtures: Composition varies; different parts are visible (e.g., copper metal in water, hot fudge sundae).

Example: Pasta and tomato sauce is a mixture; aluminum foil is a pure substance.

3.2 States and Properties of Matter

Matter exists in three primary states: solid, liquid, and gas. Each state has distinct physical properties based on particle arrangement and movement.

• Solids: Definite shape and volume; particles are close together in a fixed arrangement and move slowly.

• Liquids: Indefinite shape but definite volume; particles are close but mobile and move slowly.

• Gases: Indefinite shape and volume; particles are far apart and move rapidly.

Physical Properties: Characteristics observed or measured without changing the identity of a substance (e.g., color, melting point, density).

Physical Change: Change in state or shape without altering the substance's identity (e.g., melting ice, chopping wood).

Chemical Properties: Describe the ability of a substance to change into a new substance (e.g., burning, tarnishing).

Chemical Change: Results in the formation of new substances with different properties (e.g., caramelizing sugar, rusting iron).

3.3 Temperature

Temperature measures how hot or cold an object is, using scales such as Celsius, Fahrenheit, and Kelvin. Understanding temperature conversions is essential in chemistry.

• Celsius Scale: Freezing point of water is 0°C; boiling point is 100°C.

• Fahrenheit Scale: Freezing point of water is 32°F; boiling point is 212°F.

• Kelvin Scale: Absolute zero is 0 K; freezing point of water is 273 K; boiling point is 373 K.

Temperature Conversion Equations:

• To convert Celsius to Fahrenheit:

• To convert Fahrenheit to Celsius:

• To convert Celsius to Kelvin:

3.4 Energy

Energy is the ability to do work and makes objects move. It exists in two main forms: kinetic and potential energy.

• Kinetic Energy: Energy of motion (e.g., swimming, mowing the lawn).

• Potential Energy: Stored energy due to position or chemical composition (e.g., water at the top of a dam, gasoline in a tank).

Heat: Energy associated with the movement of particles; measured in joules (J) or calories (cal).

• 1 calorie = 4.184 joules

• 1 kilocalorie (kcal) = 1000 calories

• 1 kilojoule (kJ) = 1000 joules

3.5 Energy and Nutrition

Nutritionists use calorimeters to measure the energy content of food. Energy values are shown as Calories (Cal) or kilojoules (kJ) on food labels.

• Calorimeter: Device used to measure heat transfer during food combustion.

• Energy Values: Typical values for carbohydrates, fats, and proteins are provided in kcal or kJ per gram.

Example: To calculate the total energy in a cup of milk, sum the energy from carbohydrates, fats, and proteins using their respective values.

3.6 Specific Heat

Specific heat is the amount of heat required to raise the temperature of 1 g of a substance by 1°C. It varies for different substances and is used to calculate heat loss or gain.

• Specific Heat Equation:

• For water:

• Heat Calculation:

3.7 Changes of State

Matter changes state when it is converted from one form to another, such as melting, freezing, vaporization, condensation, sublimation, and deposition.

• Melting/Freezing: Melting is the change from solid to liquid; freezing is the reverse.

• Heat of Fusion: Amount of heat needed to melt or freeze 1 g of a substance (for water: 334 J/g).

• Sublimation/Deposition: Sublimation is the change from solid to gas; deposition is the reverse.

• Evaporation/Condensation: Evaporation is the change from liquid to gas; condensation is the reverse.

• Heat of Vaporization: Amount of heat needed to vaporize or condense 1 g of a substance (for water: 2260 J/g).

Heating and Cooling Curves

Heating and cooling curves illustrate temperature changes and changes of state as heat is added or removed. Plateaus represent changes of state at constant temperature, while sloped lines indicate temperature changes within a state.

Combined Heat Calculations

To calculate the total heat required for a substance to undergo multiple changes (e.g., warming, vaporizing), sum the heat for each step using the appropriate equations and conversion factors.

Concept Map: Matter and Energy

Matter exists as solids, liquids, or gases and can be classified as pure substances (elements or compounds) or mixtures (homogeneous or heterogeneous). Changes of state require energy (heat of fusion, heat of vaporization) and are represented by heating/cooling curves. Energy affects particle motion and is measured in calories or joules using temperature change, specific heat, and mass.