Examples of Combination Reactions:

• 2H2 + O2 → 2H2O


• N2 + 3H2 → 2NH3


• CaO + H2O → Ca(OH)2


• Fe + S → FeS


• 4Na + O2 → 2Na2O

Explanation:

Combination reactions, also known as synthesis reactions, are chemical reactions in which two or more substances combine to form a single product. In these reactions, the reactants are usually elements or compounds, and the product is always a compound.

1. 2H2 + O2 → 2H2O: This is the chemical equation for the combustion of hydrogen gas. Hydrogen gas and oxygen gas combine to form water vapor when ignited. This reaction is exothermic and releases a significant amount of heat energy.

2. N2 + 3H2 → 2NH3: This is the chemical equation for the synthesis of ammonia gas. Nitrogen gas and hydrogen gas react under high pressure and temperature, with the aid of a catalyst, to form ammonia gas. Ammonia is widely used as a fertilizer and in the production of other chemicals.

3. CaO + H2O → Ca(OH)2: This is the chemical equation for the reaction between calcium oxide and water to form calcium hydroxide, also known as slaked lime. This reaction is highly exothermic and is often used in construction and agriculture.

4. Fe + S → FeS: This is the chemical equation for the formation of iron sulfide. Iron and sulfur react to form a compound with a characteristic odor of rotten eggs. Iron sulfide is commonly found in nature and is used to produce sulfuric acid.

5. 4Na + O2 → 2Na2O: This is the chemical equation for the reaction between sodium metal and oxygen gas to form sodium oxide. This reaction is highly exothermic and releases a significant amount of heat. Sodium oxide is used as a flux in the production of glass and ceramics.