Chemical Reactions

Brief Overview

This note covers chemical reactions and was created from a 22‑page PDF presentation. It walks through reaction fundamentals, balancing equations, and the five main reaction types with examples and practice problems.

Key Points

  • Fundamental concepts of what a chemical reaction is and how to recognize it

  • Step‑by‑step guidance for balancing equations using the law of conservation of mass

  • Overview of decomposition, synthesis, single‑replacement, double‑replacement, and combustion reactions

  • Sample equations and a practice combustion problem to reinforce learning

🧪 Chemical Reaction Basics

A chemical reaction is a process where one or more substances transform into new substances through the making or breaking of chemical bonds. This involves a change in the arrangement of atoms and results in substances with different properties than the original reactants.

Evidence of Chemical Reactions: Observable changes indicating a reaction occurred, including color change, energy change (heat/light/sound), phase change, or smell change

Reaction Notation

  • (s) = solid

  • (l) = liquid

  • (g) = gas

  • (aq) = aqueous (dissolved in water)

  • Reactants → Products (arrow shows the transition)

Diatomic Elements

Diatomic elements are elements so reactive that they are not found naturally on Earth unless in diatomic form (2 atoms bonded together) or bonded with other elements.

Seven elements exist naturally in diatomic form (two atoms bonded together):

  • H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂

  • Six of these form a "7" shape on the periodic table

⚖ Balancing Chemical Reactions

Law of Conservation of Mass: Matter cannot be created or destroyed (except in nuclear reactions), so the number of each type of atom must be equal on both sides of the equation

Example: Balancing Water Formation

Unbalanced:

  • Hydrogen: 2 → 2 ✓

  • Oxygen: 2 → 1 ✗

Balanced:

  • Hydrogen: 4 → 4 ✓

  • Oxygen: 4 → 2 ✓

🔄 Types of Chemical Reactions

1. Decomposition Reactions
Format: AB → A + B
Explanation: One compound breaks down into simpler substances.

2. Synthesis Reactions
Format: A + B → AB
Explanation: Two or more substances combine to form a single compound.

3. Single Replacement Reactions
Format: A + BC → AC + B
Explanation: An element replaces another element in a compound.

4. Double Replacement Reactions
Format: AB + CD → AD + CB
Explanation: Ions are exchanged between two compounds.

5. Combustion Reactions
Format: Organic + O₂ → CO₂ + H₂O
Explanation: A substance burns in oxygen, producing water and carbon dioxide.

More In Depth


Synthesis (Combination) Reaction

  • Two or more substances combine to form one product.

  • General form: A + B → AB

  • Example: 2 H₂ + O₂ → 2 H₂O

Combustion Reaction

  • A substance reacts with oxygen to produce energy (heat/light).

  • ALWAYS Produces O₂ and H₂O (if you see that its combustion) (carbon or another substance may be In front of O2 sometimes)

  • Example: CH₄ + 2 O₂ → CO₂ + 2 H₂O

Decomposition Reaction

  • One compound breaks down into two or more simpler substances.

  • General form: AB → A + B

  • Example: 2 H₂O₂ → 2 H₂O + O₂

Single Replacement (Single Displacement) Reaction

  • One element replaces another element in a compound.

  • Has one single element and one ionic compound

  • General form: A + BC → AC + B

  • Example: Zn + CuSO₄ → ZnSO₄ + Cu

Double Replacement (Double Displacement) Reaction

  • Two ionic compounds exchange ions to form new compounds.

  • Two ionic compounds are there

  • General form: AB + CD → AD + CB

  • Example: AgNO₃ + NaCl → AgCl + NaNO₃

Brief Overview

This note covering chemical reactions was created from an 11‑page PDF presentation. It reviews evidence of reactions, state symbols, reaction formats, the five main reaction types, and provides practice links.

Key Points

  • How to spot a chemical reaction by color, energy, or phase changes

  • Meaning of state symbols and the reactants → products format

  • Summaries of combustion, decomposition, single replacement, synthesis, and double replacement reactions

  • Links to a PhET simulation and a Canvas worksheet for extra practice

Evidence of Chemical Reactions 🧪

Observable changes that indicate a chemical reaction has occurred:

  • Color change and other physical property changes

  • Energy change (heat, bright light, or sound production)

  • Phase of matter change (gas production via smell, fizzing, or solid formation)

Describing Chemical Reactions

State Symbols

  • (s) = solid

  • (l) = liquid

  • (g) = gas

  • (aq) = aqueous (dissolved in water)

Reaction Format

Reactants → Products

The arrow (→) represents the change/transition/process

Diatomic Elements ⚛

Diatomic elements are elements so reactive that they are not found naturally on Earth unless in diatomic form (2 atoms bonded together) or bonded with other elements.

Example: Hydrogen exists as , not

The 7 diatomic elements: 6 of the 7 form the shape of "7" on the periodic table