States of Matter

Characteristics of Solids, Liquids, and Gases

Understanding the properties of the three primary states of matter—solid, liquid, and gas—is fundamental in chemistry. Each state is defined by the arrangement and movement of its particles.

• Solids: Have a definite shape and volume. Particles are closely packed in fixed positions and vibrate in place.

• Liquids: Have a definite volume but take the shape of their container. Particles are close together but move more freely than in solids.

• Gases: Have neither definite shape nor volume. Particles are far apart and move rapidly in all directions.

Example: Ice (solid), water (liquid), and steam (gas) are all forms of H2O.

Properties Comparison Table

Physical and Chemical Changes

Physical Changes

A physical change alters the form or appearance of matter but does not change its composition. No new substances are formed.

• Examples: Melting ice, boiling water, dissolving sugar in water, cutting a rope, making ice cubes.

Chemical Changes

A chemical change (chemical reaction) results in the formation of one or more new substances with different properties from the original.

• Examples: Burning sugar, baking a cake, fermenting grapes to produce wine, digesting a meal.

Comparison Table: Physical vs. Chemical Changes

Changes of State

Phase Transitions

Substances can change from one state of matter to another through physical processes called phase transitions.

• Melting: Solid to liquid

• Freezing: Liquid to solid

• Boiling (Vaporization): Liquid to gas

• Condensation: Gas to liquid

• Sublimation: Solid directly to gas

• Deposition: Gas directly to solid

Example: Dry ice (solid CO2) sublimes directly to gas at room temperature.

Energy in Chemistry

Types of Energy

Energy is the capacity to do work or produce heat. In chemistry, energy is often discussed in terms of its forms and how it is stored or transferred.

• Kinetic Energy: Energy of motion. The faster the particles move, the greater their kinetic energy.

• Potential Energy: Stored energy due to position or composition.

Example: Molecules in steam at 110°C have more kinetic energy than those in ice at -20°C.

Temperature and Energy

Temperature is a measure of the average kinetic energy of particles in a substance. The Kelvin scale is the SI unit for temperature in scientific contexts.

• Conversion from Fahrenheit to Kelvin:

Example: -55°F corresponds to 225 K.

Caloric Content of Foods

Calculating Energy from Food

Foods provide energy measured in kilocalories (kcal). The caloric values for macronutrients are standardized:

• Carbohydrate: 4 kcal/g

• Protein: 4 kcal/g

• Fat: 9 kcal/g

Example Calculation: A potato with 20 g carbohydrate provides kcal.

For a food containing 15 g protein, 1 g fat, and 42 g carbohydrate:

• Protein: kcal

• Fat: kcal

• Carbohydrate: kcal

• Total: kcal (rounded to 240 kcal for significant figures)

Summary Table: Caloric Values of Macronutrients

Key Terms and Definitions

• Physical Change: A change that does not alter the chemical composition of a substance.

• Chemical Change: A process in which one or more substances are converted into new substances.

• Sublimation: The process by which a solid changes directly to a gas without passing through the liquid state.

• Deposition: The process by which a gas changes directly to a solid.

• Kinetic Energy: The energy of motion.

• Potential Energy: The energy stored due to position or composition.