Question

1. a student left an iron nail outside for several weeks, and it formed reddish - brown rust. which explanation best describes this chemical change?

a) the iron nail absorbed water and expanded physically.
b) the iron reacted with oxygen and moisture to form a new compound, fe₂o₃.
c) the nail was only coated with dirt from the environment.
d) the mass of the nail decreased because atoms were destroyed.

Explanation:

• Option A: Absorbing water and expanding physically is a physical change, not a chemical change. Rusting is a chemical change, so A is incorrect.
• Option B: Iron reacts with oxygen (\(O_2\)) and moisture (\(H_2O\)) in a chemical reaction to form rust (\(Fe_2O_3\cdot xH_2O\), simplified as \(Fe_2O_3\) in basic chemistry explanations). This is a chemical change as new substances are formed.
• Option C: Rusting is a chemical reaction, not just coating with dirt. Dirt coating would be a physical process. So C is wrong.
• Option D: In a chemical reaction (rusting), atoms are rearranged, not destroyed. According to the law of conservation of mass, the mass of the nail (reactant) plus the mass of reactant oxygen and water (if we consider the full system) is equal to the mass of rust (product). The mass of the nail itself (as iron) seems to change because it combines with other elements, but atoms are not destroyed. So D is incorrect.

Answer:

B. The iron reacted with oxygen and moisture to form a new compound, \(Fe_2O_3\).