What are the different types of reactions in physical science?

There are five main categories of chemical reactions recognized in physical science: synthesis, decomposition, combustion, single replacement (or single displacement), and double replacement (or double displacement).

Types of Chemical Reactions

Here's a breakdown of each type:

1. Synthesis Reactions

• Definition: A synthesis reaction occurs when two or more reactants combine to form a single, more complex product.
• General Form: A + B → AB
• Example: 2H₂ (g) + O₂ (g) → 2H₂O (l) (Hydrogen and oxygen combine to form water.)

2. Decomposition Reactions

• Definition: A decomposition reaction occurs when a single reactant breaks down into two or more simpler products.
• General Form: AB → A + B
• Example: 2H₂O (l) → 2H₂ (g) + O₂ (g) (Water decomposes into hydrogen and oxygen through electrolysis.)

3. Combustion Reactions

• Definition: A combustion reaction is a rapid reaction between a substance with an oxidant, usually oxygen, to produce heat and light. This often involves a hydrocarbon reacting with oxygen to produce carbon dioxide and water.
• General Form: Fuel + O₂ → CO₂ + H₂O (+ Heat & Light)
• Example: CH₄ (g) + 2O₂ (g) → CO₂ (g) + 2H₂O (g) (Methane reacts with oxygen to produce carbon dioxide and water.)

4. Single Replacement Reactions

• Definition: A single replacement reaction occurs when one element replaces another element in a compound. Whether or not a reaction will occur depends on the relative reactivity of the elements involved, typically determined using an activity series.
• General Form: A + BC → AC + B
• Example: Zn (s) + 2HCl (aq) → ZnCl₂ (aq) + H₂ (g) (Zinc replaces hydrogen in hydrochloric acid.)

5. Double Replacement Reactions

• Definition: A double replacement reaction occurs when the positive ions (cations) of two reactants switch places, forming two new compounds. These reactions often result in the formation of a precipitate (an insoluble solid), a gas, or water.
• General Form: AB + CD → AD + CB
• Example: AgNO₃ (aq) + NaCl (aq) → AgCl (s) + NaNO₃ (aq) (Silver nitrate reacts with sodium chloride to form silver chloride, a precipitate, and sodium nitrate.)