1. Formation of Water:

* Hydrogen gas (H₂) reacts with oxygen gas (O₂) to produce water (H₂O).

* Equation: 2H₂ + O₂ → 2H₂O

2. Formation of Magnesium Oxide:

* Magnesium metal (Mg) reacts with oxygen gas (O₂) to produce magnesium oxide (MgO).

* Equation: 2Mg + O₂ → 2MgO

3. Formation of Sodium Chloride:

* Sodium metal (Na) reacts with chlorine gas (Cl₂) to produce sodium chloride (NaCl), also known as table salt.

* Equation: 2Na + Cl₂ → 2NaCl

4. Formation of Iron (III) Oxide (Rust):

* Iron (Fe) reacts with oxygen (O₂) in the presence of moisture to form iron (III) oxide (Fe₂O₃), commonly known as rust.

* Equation: 4Fe + 3O₂ → 2Fe₂O₃

5. Formation of Calcium Carbonate:

* Calcium oxide (CaO), also known as lime, reacts with carbon dioxide (CO₂) to produce calcium carbonate (CaCO₃).

* Equation: CaO + CO₂ → CaCO₃

Key Characteristics of Combination Reactions:

* Two or more reactants combine to form a single product.

* The product is a compound with a different chemical formula than the reactants.

* Energy is often released in the form of heat or light (exothermic reaction), but sometimes energy is absorbed (endothermic reaction).