When lithium is mixed with hydrochloric acid (HCl), it undergoes a chemical reaction to produce lithium chloride (LiCl) and hydrogen gas (H2). The reaction can be represented as follows:

2Li + 2HCl → 2LiCl + H2

In this reaction, lithium atoms lose one valence electron each to form Li+ ions, while hydrogen atoms gain one valence electron each to form H2 molecules. The reaction is highly exothermic, meaning it releases a significant amount of heat.

The reaction between lithium and hydrochloric acid is a classic example of a single-displacement reaction, where a more reactive metal replaces a less reactive metal in a compound. Lithium is more reactive than hydrogen, so it is able to displace hydrogen from the hydrochloric acid.

It is important to note that this reaction should only be carried out under controlled conditions, as it can be potentially hazardous due to the release of flammable hydrogen gas and the corrosive nature of hydrochloric acid.