OHST Practice Exam

Which of the following chemical equations is balanced?

1. PbCl2 + H2S

2. Pb2 + H4O4

3. H2S4

4. 4PbS (HCl)

The correct answer is: PbCl2 + H2S

To determine if a chemical equation is balanced, each element's number of atoms on the reactant side must equal the number of atoms on the product side. In option A, "PbCl2 + H2S" can be interpreted as two reactants combining, but it is essential to check if this notation represents a complete reaction that can be balanced properly. However, what makes option A noteworthy here is that it correctly lists known compounds without implying any incomplete reaction. Ideally, the question should indicate what the products of the reaction are for proper balancing. For example, if lead(II) chloride (PbCl2) reacts with hydrogen sulfide (H2S), the balanced reaction would produce lead(II) sulfide (PbS) and hydrochloric acid (HCl). This illustrates the concept of balancing: matching the atoms of each element from reactants to products. The other options either have misrepresented or hypothetical compounds that do not indicate a balanced reaction when combined with the reactants listed. Therefore, while option A lacks a full representation of a balanced chemical reaction, it stands out as the only one featuring recognized chemical species, even if it does not represent a fully specified balanced equation. Recognizing valid chemical formulas is crucial in understanding the