4.1 Introductions for Reactions

Page 1: Introduction to Reactions

Learning Objective

• 4.1.A: Identify evidence of chemical and physical changes in matter.

Essential Knowledge

• Physical Change:

  • Definition: A change in properties but not in composition.

  • Examples: Changes in phase (solid, liquid, gas), formation/separation of mixtures.

• Chemical Change:

  • Definition: Transformation into new substances with different compositions.

  • Evidence: Production of heat/light, gas, precipitate formation, color change.

Key Concepts

• Matter: Material that occupies space and has mass.

• Mixtures:

  • Homogeneous Mixture: Indistinguishable parts.

  • Heterogeneous Mixture: Distinguishable parts.

• Pure Substance: Constant composition; can’t be separated by physical means.

• Compound: Can be broken down into elements by chemical processes.

• Elements: Cannot be decomposed into simpler substances.

Physical Change Characteristics

• Physical properties change without changing composition.

• Particle arrangement differs in solid, liquid, and gas:

  • Solid: Rigid structure, definite shape and size.

  • Liquid: Particles close but move freely, definite volume, fluid shape.

  • Gas: Occupies full volume of container; shape and volume defined by it.

Page 2: Additional Physical Changes and Chemical Changes

Physical Changes Overview

• Examples:

  • Separations of Mixtures:

    • Distillation: Based on boiling points.

    • Filtration: Based on particle size.

    • Chromatography: Based on intermolecular forces.

  • Deformation:

    • Cutting, denting, tearing, stretching.

  • Making Solutions:

    • Atoms remain unchanged in physical changes.

• Reversible Nature: Physical changes are often reversible.

Chemical Change Characteristics

• Changes in property due to bond breaking and formation.

• Evidence of a chemical reaction:

  • Production of precipitate, color change, light, temperature change, sounds, gas formation.

• Types of Chemical Reactions:

  • Composition (Synthesis): A + B → AB

  • Decomposition: AB → A + B

  • Single Ionic Replacement: A + BC → AC + B

  • Double Ionic Replacement: AB + CD → AD + CB

  • Combustion: CₓHᵧ + O₂ → CO₂ + H₂O

• Exclusions: Double ionic replacement reactions do not include RedOx reactions.

Page 3: Types and States of Matter

Activities

• Describe types of matter and states of matter using images.

• Decide if a chemical or physical change has occurred in given scenarios:

  • Example 1: Iodine solution losing color.

  • Example 2: Hole appearing from acid on fabric.

  • Example 3: Precipitate formation from mixing solutions.

  • Example 4: Dry Ice sublimation creating fog.

• Molecular Drawings: Create drawings for various mixtures and reactions.

• Analyze the reaction between hydrochloric acid and sodium hydroxide regarding physical or chemical changes.

Page 4: Identifying Changes in Reactions

Identify Changes

• Classify the following reactions as chemical or physical:

  • a) 2H₂O (g) → 2H₂ (g) + O₂ (g) (Chemical)

  • b) NH₄Cl (s) → NH₃ (g) + HCl (g) (Chemical)

  • c) H₂O (s) → H₂O (l) (Physical)

  • d) C₈H₈ (l) → 2C₄H₄ (g) (Chemical)

  • e) 2Al₂O₃ (s) → 4Al (s) + 3O₂ (g) (Chemical)

  • f) C₃H₆O (l) → C₃H₆O (g) (Physical)

  • g) NaHCO₃ (s) + HCH₃COO (aq) → CO₂ (g) + H₂O (l) + NaCH₃COO (aq) (Chemical)

Mixtures vs. Pure Compounds

• Assess characteristics of substances to identify them as mixtures or pure compounds and determine the nature of changes:

  • a) Heating a clear solid giving off gas and leaving a metal behind (Chemical).

  • b) Heating a brown liquid producing a new liquid and leaving a residue (Chemical).

  • c) Dissolving sugar in tea for a sweeter taste (Physical).

  • d) Combining a gray metal and colorless gas forming a flaky solid (Chemical).