Evolution of a gas:
An example of a chemical reaction that shows the evolution of a gas is the reaction between baking soda (sodium bicarbonate) and vinegar (acetic acid).

1. Introduction:
When baking soda and vinegar are mixed together, a chemical reaction occurs, resulting in the formation of carbon dioxide gas.

2. Chemical equation:
The chemical equation for this reaction is:
NaHCO3 (sodium bicarbonate) + CH3COOH (acetic acid) → CO2 (carbon dioxide) + H2O (water) + NaCH3COO (sodium acetate)

3. Explanation:
a) Sodium bicarbonate (NaHCO3) is a white solid, and acetic acid (CH3COOH) is a clear liquid.
b) When these two substances are combined, the following reaction takes place:
- The acetic acid donates a hydrogen ion (H+) to the bicarbonate ion (HCO3-) from baking soda, forming water (H2O) and carbonic acid (H2CO3).
- Carbonic acid is unstable and decomposes into carbon dioxide gas (CO2) and water (H2O).
c) Carbon dioxide gas is released as bubbles, which can be observed as effervescence or fizzing.
d) The evolved carbon dioxide gas is responsible for the bubbles and the fizzing sensation.

Change of colors:
An example of a chemical reaction that involves a change of colors is the reaction between potassium iodide and lead(II) nitrate.

1. Introduction:
When potassium iodide and lead(II) nitrate are mixed together, a chemical reaction occurs, resulting in the formation of a yellow precipitate.

2. Chemical equation:
The chemical equation for this reaction is:
2KI (potassium iodide) + Pb(NO3)2 (lead(II) nitrate) → 2KNO3 (potassium nitrate) + PbI2 (lead(II) iodide)

3. Explanation:
a) Potassium iodide is a white solid, and lead(II) nitrate is a clear liquid.
b) When these two substances are combined, the following reaction takes place:
- The potassium iodide reacts with the lead(II) nitrate to form potassium nitrate and lead(II) iodide.
- Lead(II) iodide is a bright yellow precipitate that is insoluble in water.
c) The formation of the yellow precipitate indicates a change in color during the reaction.
d) This color change can be easily observed and serves as evidence of a chemical reaction.

Formation of precipitate:
An example of a chemical reaction that involves the formation of a precipitate is the reaction between silver nitrate and sodium chloride.

1. Introduction:
When silver nitrate and sodium chloride are mixed together, a chemical reaction occurs, resulting in the formation of a white precipitate.

2. Chemical equation:
The chemical equation for this reaction is:
AgNO3 (silver nitrate) + NaCl (sodium chloride) → AgCl (silver chloride) + NaNO3 (sodium nitrate)

3. Explanation:
a) Silver nitrate is a clear liquid, and sodium chloride is a white solid.
b) When these two substances are combined, the following reaction takes place:
- The silver nitrate reacts with the sodium chloride to form silver chloride and sodium nitrate.

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