What type of chemical reaction takes place when i) limestone is heated?

ii) a magnesium ribbon is burnt in air?

When discussing chemical reactions, it's important to understand the specific processes that occur during different reactions. Here’s a breakdown of the reactions you asked about:

Heating Limestone

When limestone, primarily composed of calcium carbonate (CaCO₃), is heated, it undergoes a process called thermal decomposition. This reaction can be represented as:

• CaCO₃ (s) → CaO (s) + CO₂ (g)

In this reaction, calcium carbonate breaks down into calcium oxide (quicklime) and carbon dioxide gas. This is a common reaction used in the production of lime for various industrial applications.

Burning Magnesium in Air

When a magnesium ribbon is burned in air, it reacts with oxygen to form magnesium oxide. This reaction is an example of a combustion reaction, and it can be represented as:

• 2Mg (s) + O₂ (g) → 2MgO (s)

During this process, magnesium burns brightly, producing a white ash of magnesium oxide. This reaction releases a significant amount of energy in the form of light and heat.