Chapter 3 – Matter and Energy: Study Notes

Chapter 3 – Matter and Energy

Section 3.1: Classification of Matter

Matter is the material that makes up all things in the universe. It is anything that has mass and occupies space. Matter can be classified according to its composition into pure substances and mixtures.

• Pure Substances: A type of matter with a fixed or definite composition.

  • Element: Composed of only one type of atom (e.g., copper, gold, helium).

  • Compound: Composed of two or more elements always combined in the same proportion (e.g., water, hydrogen peroxide).

• Mixtures: Consist of two or more substances that are physically mixed but not chemically combined. The substances can be present in different proportions and can be separated by physical methods.

  • Homogeneous Mixture (Solution): The composition is uniform throughout, and the different parts are not visible (e.g., brass, salt water, air).

  • Heterogeneous Mixture: The composition varies from one part to another, and the different parts are visible (e.g., salad, sand and water, trail mix).

Example: Aluminum foil is a pure substance (element), while pasta and tomato sauce is a mixture.

Section 3.2: States and Properties of Matter

Matter exists in three primary states: solid, liquid, and gas. Each state has distinct properties based on the arrangement and movement of its particles.

• Solids:

  • Definite shape and volume

  • Particles are close together in a fixed arrangement

  • Particles move very slowly (vibrate in place)

• Liquids:

  • Indefinite shape but definite volume

  • Take the shape of their container

  • Particles are close together but can move past each other (mobile)

  • Particles move at moderate speed

• Gases:

  • Indefinite shape and volume

  • Take the shape and volume of their container

  • Particles are far apart and move very fast

Physical and Chemical Properties and Changes

Physical Properties

• Observed or measured without changing the identity of a substance

• Examples: shape, physical state, boiling and freezing points, density, color

Physical Changes

• No change in the identity or composition of the substance

• Includes changes in state (e.g., melting, boiling) or physical shape (e.g., cutting, grinding)

Examples: Water boiling, sugar dissolving in water, copper drawn into wires, paper cut into pieces, pepper ground into flakes.

Chemical Properties and Changes

• Describe the ability of a substance to interact with other substances or change into a new substance

• During a chemical change, the original substance is turned into one or more new substances with new composition, chemical, and physical properties

Example: Burning methane gas: $\mathrm{CH_4} + 2\,\mathrm{O_2} \rightarrow \mathrm{CO_2} + 2\,\mathrm{H_2O}$

Section 3.3: Temperature

Temperature measures how hot or cold an object is compared to another object. It indicates the direction of heat flow (from higher to lower temperature) and is measured using a thermometer.

Temperature Scales

• Celsius (°C): 0°C is the freezing point and 100°C is the boiling point of water (100 degrees between them).

• Fahrenheit (°F): 32°F is the freezing point and 212°F is the boiling point of water (180 degrees between them).

• Kelvin (K): Absolute zero (0 K) is the lowest possible temperature (−273.15°C). No negative values. 1 K = 1°C.

Temperature Conversion Equations

• From Celsius to Fahrenheit: $T_F = 1.8\,T_C + 32$

• From Fahrenheit to Celsius: $T_C = \frac{T_F - 32}{1.8}$

• From Celsius to Kelvin: $T_K = T_C + 273.15$

Example: A body temperature of 34.8°C is $T_F = 1.8 \times 34.8 + 32 = 94.6\,°F$.

Section 3.4: Energy

Energy is the ability to do work or produce heat. It makes objects move and can be transferred or transformed between objects and systems.

• Work: $\text{Work} = \text{Force} \times \text{Distance}$

Kinetic and Potential Energy

• Potential Energy: Energy based on position or chemical composition (e.g., a compressed spring, water at the top of a dam).

• Kinetic Energy: Energy associated with motion (e.g., a moving car, water flowing over a dam).

Energy as Heat

• Heat is the energy associated with the movement of particles.

• The faster the particles move, the greater the heat or thermal energy.

Example: As heat is added to an ice cube, the H2O molecules move faster, eventually melting the ice.

Units of Energy

• SI unit: joule (J); 1 kJ = 1000 J

• Other units: calorie (cal); 1 kcal = 1000 cal

• 1 cal = 4.184 J (exact)

Section 3.5: Energy and Nutrition

On food labels, energy is shown as the nutritional Calorie (with a capital C), which is equivalent to 1 kilocalorie (kcal) or 1000 calories (cal). In other countries, energy may be shown in kilojoules (kJ).

Caloric Food Values

Food Type	kcal/g	kJ/g
Carbohydrate	4	17
Fat	9	38
Protein	4	17

Example Calculation: A cup of whole milk contains 13 g carbohydrate, 9 g fat, and 9 g protein. Total kcal = $(13 \times 4) + (9 \times 9) + (9 \times 4) = 169$ kcal.

Section 3.6: Specific Heat (SH or c)

Specific heat is the amount of heat required to raise the temperature of exactly 1 g of a substance by exactly 1°C. Each substance has a unique specific heat value.

• Formula: $SH \text{ or } c = \frac{\text{heat}}{\text{mass} \times \Delta T} = \frac{q}{m \cdot \Delta T} = \frac{\text{cal or J}}{\text{g} \cdot ^\circ\text{C}}$

• Temperature change: $\Delta T = T_{\text{final}} - T_{\text{initial}}$

Heat Equation

• To calculate heat energy: $q = m c \Delta T$

Table: Specific Heats for Some Substances

Substance	cal/g°C	J/g°C
Aluminum (Al)	0.214	0.897
Copper (Cu)	0.0920	0.386
Gold (Au)	0.0308	0.129
Iron (Fe)	0.108	0.452
Silver (Ag)	0.0562	0.235
Titanium (Ti)	0.125	0.523
Water (H2O)	1.00	4.184

Example: To find the heat needed to raise the temperature of 16 g of titanium (SH = 0.125 cal/g°C) from 36.0°C to 41.3°C: $q = m c \Delta T = 16 \times 0.125 \times (41.3 - 36.0) = 10$ cal

Calculations Using Specific Heat

• Calculate the heat lost or gained by measuring mass and temperature change when the specific heat is known.

• Calculate the specific heat by measuring mass, temperature change, and heat lost or gained.

Formulas: Heat (cal) = mass (g) × temperature change (°C) × specific heat (cal/g°C) Heat (J) = mass (g) × temperature change (°C) × specific heat (J/g°C)

Practice and Application

• Identify pure substances and mixtures in everyday life.

• Classify changes as physical or chemical.

• Convert between temperature scales using the provided equations.

• Calculate energy content in food and heat transfer in physical processes.