Final answer:
A balanced chemical reaction must have equal numbers of atoms for each element and equal total charge on both sides of the equation. Adjusting coefficients achieves balance without changing the chemical identities represented by subscripts. An imbalanced reaction needs to be adjusted for the conservation of mass and charge.
Step-by-step explanation:
In the context of a chemical reaction, a statement can be about whether the reaction is balanced or not. This requires checking if both the number of atoms and the oxidation states of reactants and products are equal on both sides of the equation. When a reaction is balanced, it adheres to the law of conservation of mass, meaning that the number of atoms for each element, as well as the total charge, are the same on both sides. If the numbers match, the chemical identities remain consistent, and the reaction properly represents the conservation.
In the provided examples, whether 2H2 + O2 → 2H2O or any other reaction, one must check the atoms of each element and the total charge to verify balance. Adjusting coefficients is the correct method to achieve this balance, since altering the subscripts would change the chemical identities of the substances involved. For example, changing H2O to H2O2 would represent hydrogen peroxide rather than water, thereby incorrectly modifying the qualitative meaning of the equation.
An imbalanced reaction where the oxidation states and atom counts do not match, such as Cr2+ + Cl2, suggests that the reaction cannot be correctly described until it is balanced, often through changing coefficients to match the conservation of mass and charge.