Which of the following must be the same before and after a chemical reaction?
Answer: The sum of the masses of all substances involved and the number of atoms of each type involved. WHY?
The law of conservation (of mass) (or matter) says mass (or matter) can't be created or destroyed. Therefore, if you start with a total of x grams you must end up with a total of x grams. And if you start with 14 N atoms or 26 O atoms you must end up with 14 N atoms and 26 O atoms. They may be arranged differently from start to end but the number must be the same.
The law of conservation of mass states that the total mass of all substances involved in a chemical reaction must remain constant before and after the reaction. This means that the sum of the masses of all the reactants (starting substances) must be equal to the sum of the masses of all the products (substances formed as a result of the reaction).
This principle is based on the fact that atoms cannot be created or destroyed during a chemical reaction; they are merely rearranged. The number and types of atoms before the reaction should be the same after the reaction, although their arrangement may be different.
If the total mass or the number of atoms involved were to change before and after the reaction, it would violate the law of conservation of mass. Therefore, to adhere to this fundamental law, the sum of the masses and the number of atoms of each type involved must remain the same before and after a chemical reaction.
To understand why the sum of masses and the number of atoms must be the same before and after a chemical reaction, let's first explain the concept of a balanced chemical equation.
A chemical equation represents a chemical reaction by using chemical formulas and coefficients. The reactants are written on the left side of the equation, while the products are written on the right side. The coefficients represent the number of molecules or formula units involved in the reaction.
For example, consider the simple chemical equation: 2H2 + O2 --> 2H2O
This equation represents the reaction of hydrogen gas (H2) with oxygen gas (O2) to form water (H2O).
In a chemical reaction, the atoms do not disappear or appear out of nowhere. The total number of atoms before the reaction must be equal to the total number of atoms after the reaction. This principle follows the law of conservation of mass and the law of conservation of atoms.
The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction, but it can only be rearranged. This means that the total mass of the reactants must be equal to the total mass of the products.
The law of conservation of atoms states that the total number of atoms of each element must be conserved in a chemical reaction. This means that the number of atoms of each element on the left side of the equation must be the same as the number on the right side of the equation.
In our example equation, 2H2 + O2 --> 2H2O, there are two hydrogen atoms and two oxygen atoms on both sides of the equation. The coefficient "2" in front of the compounds ensures that we have an equal number of atoms of each element on both sides.
If the number of atoms or the total mass were different before and after the reaction, it would violate these fundamental principles and the conservation laws.
In conclusion, the total mass of all substances involved in a chemical reaction and the number of atoms of each element must remain the same before and after the reaction in order to satisfy the laws of conservation of mass and atoms.