Chemical Reaction and Equations — Important Questions

Burning of coal

Step 1: Understand that exothermic reactions release heat energy to surroundings. Step 2: Analyze each option - melting, boiling, and sublimation all require heat input (endothermic). Step 3: Burning of coal involves combustion with oxygen, releasing heat and light. Step 4: This heat energy is what we use for cooking, heating homes, and running steam engines. Step 5: The reaction C + O₂ → CO₂ + heat energy clearly shows heat as a product, making it exothermic.

Hydrogen

Step 1: Identify oxidation as the gain of oxygen or loss of electrons. Step 2: Observe that hydrogen (H₂) combines with oxygen to form water. Step 3: Hydrogen gains oxygen in this process, meeting the definition of oxidation. Step 4: Oxygen is reduced as it combines with hydrogen (reduction is opposite of oxidation). Step 5: This is the fundamental reaction in fuel cells and rocket engines, where hydrogen acts as fuel by getting oxidized.

Oxygen and moisture

Step 1: Understand that corrosion is an oxidation process requiring specific conditions. Step 2: Recognize that pure oxygen alone cannot cause rusting without water. Step 3: Similarly, water alone without oxygen cannot cause rusting. Step 4: Both oxygen (from air) and moisture (water) must be present together. Step 5: This explains why iron objects in dry desert air or underwater (low oxygen) rust much slower, and why painting prevents both air and moisture contact.

Galvanization

Step 1: Identify that zinc coating on iron is specifically called galvanization. Step 2: Understand that zinc is more reactive than iron and gets oxidized preferentially. Step 3: This means zinc corrodes first, protecting the underlying iron. Step 4: The process involves dipping iron objects in molten zinc to form a protective layer. Step 5: Common examples include galvanized iron sheets used for roofing and galvanized buckets that resist rusting much longer than plain iron.