Question

What is the difference between the following two types of reaction?
$AgN{O_3} + HCl \to AgCl + HN{O_3}$
$Mg + 2HCl \to MgC{l_2} + {H_2}$

Answer 1

A chemical reaction occurs when the bonds between reactant molecules are broken and new bonds are formed between product molecules, resulting in the formation of a new substance. Reactants are molecules that combine to make new compounds, whereas products are newly formed compounds.

Complete answer:
$AgN{O_3} + HCl \to AgCl + HN{O_3}$
The above reaction is a double displacement reaction. The ions of silver nitrate and hydrogen chloride are exchanged.
A double displacement reaction occurs when two reactants exchange ions, resulting in the formation of two new molecules. Ionic compounds dissolved in water undergo a lot of double displacement processes. The general equation represents a double replacement reaction.
$Mg + 2HCl \to MgC{l_2} + {H_2}$
The above reaction is a single displacement reaction. Here magnesium displaces hydrogen from hydrogen chloride.
A single displacement reaction, also known as a single replacement reaction, is a type of oxidation-reduction chemical reaction in which an ion or element moves out of a compound, replacing one element with another.
Applications of double displacement reactions
Indigestion caused by stomach acid
Metals are extracted.
Photometry of flames

Note:
In double substitution reactions, two ionic compounds exchange anions or cations. When the reactants are acid and base, neutralization reactions occur, and neutralization reactions are generally favourable as long as the reaction requires a solid acid and/or base.