Baking soda, also known as sodium bicarbonate (NaHCO3), undergoes a chemical change when it is heated or combined with an acid. Here are the key chemical reactions and changes involved:

1. Thermal Decomposition:

- When baking soda is heated, it undergoes thermal decomposition. This process breaks down the sodium bicarbonate into its components: carbon dioxide (CO2) gas, water (H2O), and sodium carbonate (Na2CO3).

- Chemical equation: 2NaHCO3 (s) → CO2 (g) + H2O (g) + Na2CO3 (s)

2. Reaction with Acids:

- Baking soda reacts with acids, such as vinegar (acetic acid, CH3COOH), to release carbon dioxide gas. This reaction is commonly used as a leavening agent in baking.

- Chemical equation: NaHCO3 (s) + CH3COOH (aq) → CO2 (g) + H2O (l) + CH3COONa (aq)

Here, sodium acetate (CH3COONa) is formed as a byproduct.

The release of carbon dioxide gas in both cases creates bubbles that expand and lighten the mixture, resulting in a fluffy texture in baked goods or creating the fizz and effervescence in carbonated beverages like soda.

It's important to note that the chemical changes in baking soda are irreversible. Once the carbon dioxide gas is released, it cannot be converted back into baking soda.