What is a chemical equation? What basic law of chemistry should it comply with?

Conditional notation of a chemical reaction using chemical formulas and mathematical signs.
The law of conservation of the mass of substances: the mass of substances that have entered into a chemical reaction (reagents) is equal to the mass of substances resulting from it (reaction products).

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.