Question

1. a chemical equation is balanced by changing or adding ____.

○ coefficients
○ reactants
○ chemical symbols
○ subscripts

Explanation:

• Coefficients: These are the numbers placed in front of chemical formulas in a chemical equation. By changing or adding coefficients, we can balance the number of atoms of each element on both sides of the equation while keeping the identity of the substances (reactants and products) unchanged. For example, in the equation \(2H_2 + O_2

ightarrow2H_2O\), the coefficients \(2\) (for \(H_2\)) and \(2\) (for \(H_2O\)) are used to balance the hydrogen and oxygen atoms.

• Reactants: Changing or adding reactants would change the substances involved in the reaction, not just balance the equation. The goal of balancing is to adjust the amounts of existing reactants and products (in terms of atom counts), not introduce new reactants.
• Chemical symbols: Chemical symbols represent the elements. Changing chemical symbols would change the identity of the elements involved, which is not the purpose of balancing an equation. We need to keep the elements (and thus their symbols) the same while balancing.
• Subscripts: Subscripts are part of the chemical formula and indicate the number of atoms of an element in a molecule. Changing subscripts would change the substance itself. For example, \(H_2O\) (water) is different from \(H_2O_2\) (hydrogen peroxide). We cannot change subscripts to balance an equation as it alters the compound.

Answer:

coefficients