Meaning and mechanism
In typical chemical reactions, the types of atomic nuclei are maintained, and the bonds between atoms are rearranged. Therefore, the number of atoms of each element is kept equal between the reactants and the products.
In 2H₂+O₂→2H₂O, the coefficients give the ratio of molecule counts or amounts in moles: 2:1:2. Changing an oxygen subscript to balance the equation would change the identity of oxygen or water.
Relationships and conditions
For each element, we compare the two sides by calculating the sum of the atomic numbers in the chemical formula, multiplied by the corresponding coefficient. After verifying that the sums match, we divide by the greatest common factor of the coefficients to express the result as the smallest integer ratio.
An ionic equation must conserve total charge as well as the number of atoms. Stoichiometric mole ratios and mass ratios are not numerically the same because the substances have different molar masses.
What to observe in the simulation
The subscripts in the chemical formula are not changed, but only the coefficients are adjusted. If you preserve the number of atoms and then divide the coefficient by the greatest common divisor, you get the minimum integer ratio.
It is a model that counts the number of atoms in five specified reactions. The particle picture refers to a bundle of molecules or chemical formula units and does not mean that iron and iron oxide exist as independent molecules. The bonding structure, reaction conditions, reaction rate, and yield are not calculated. The unit of numbers in bars and tables is the number of atoms.
Key relationships and symbols
Number of atoms before reaction of each element = Number of atoms after reaction
| Symbol | Meaning | Unit |
|---|---|---|
| ν | Stoichiometric coefficient | Dimensionless |
| ν × number of atoms | Number of atoms contributed by that substance | Particle-count or mole ratio |
Worked example
What is the minimum whole number ratio between 2H₂ + O₂ → 2H₂O and 4H₂ + 2O₂ → 4H₂O?
In both formulas, the number of atoms per element is the same, but 4:2:4 can be divided by the common divisor of 2. Use a ratio where the greatest common divisor of positive integer coefficients is 1.
Common misconceptions
- In the reaction, the permissible adjustments are coefficients, and this is not simply arbitrarily changing the stoichiometric subscripts.