Question

Is the number of atoms of each element conserved during a chemical reaction? How about the total number of moles?

Short answer

How about the total number of moles? Answer: The number of atoms of each element is conserved during a chemical reaction, as required by the conservation of mass. However, the total number of moles is not necessarily conserved during a chemical reaction. Although the number of moles of each type of atom is conserved, the total number of moles of molecules can change.

Step-by-step solution

Understanding Conservation of Mass and the Mole Concept

Conservation of mass states that the total mass of all substances before a chemical reaction (reactants) is equal to the total mass of substances after the reaction (products). The mole concept helps us to simplify the counting of particles in a chemical reaction. One mole of any substance contains 6.022 x 10^23 atoms, molecules, or ions. A balanced chemical equation shows the mole ratio between reactants and products.

Balancing a Chemical Equation

Consider a simple chemical reaction: H2 (g) + O2 (g) → H2O (l) Here, hydrogen gas reacts with oxygen gas to form water. To ensure that the number of atoms of each element is conserved (i.e., the same before and after the reaction), we need to balance this equation. After balancing, the equation becomes: 2H2 (g) + O2 (g) → 2H2O (l)

Counting Atoms and Moles in the Balanced Equation

Now we can count the number of atoms and moles for each element in the balanced chemical equation: Reactants: - 2 moles of H2 (g) contain 4 moles of H atoms - 1 mole of O2 (g) contains 2 moles of O atoms Total moles of atoms = 4 moles of H atoms + 2 moles of O atoms = 6 moles Products: - 2 moles of H2O (l) contain 4 moles of H atoms and 2 moles of O atoms Total moles of atoms = 4 moles of H atoms + 2 moles of O atoms = 6 moles

Answering the Questions

1. The number of atoms of each element is conserved during the chemical reaction. In our example, the number of H atoms and O atoms are the same on both sides of the balanced equation, as required by the conservation of mass. 2. The total number of moles is not necessarily conserved during a chemical reaction. Although the number of moles of each type of atom is conserved, the total number of moles of molecules can change. In our example, we have 3 moles of molecules as reactants (2 moles of H2 and 1 mole of O2) and 2 moles of H2O as the product. The total number of moles of molecules changed during the reaction. However, the total number of moles of atoms (6 moles) remains the same on both sides.