Question

What properties do all chemical reactions have in common?

Answer 1

Answer. The common properties of chemical reactions are:

Temperature: Change in temperature will be there. This change can be increase in  temperature (exothermic) or decrease in temperature (endothermic).

Formation of  product: The product will be formed if the chemical reaction has taken place. Product formed can be in any state (solid, liquid or gas). This formation of product can be observed by looking out for change in color, change in odour or substance getting disappeared.

Number of products: Minimum number of products formed after chemical reaction is one. More than one number of products can be formed.

Answer 2

What all chemical reactions have in common is that energy is released in various forms. Sometimes it's heat or light when there's an explosion, or theres gas and odors or a change in color, or sometimes solids are formed as a deposit. This all show that a reaction occurred and are used as proof.