Great News!
Many students who study using our platform have reported that a large number of the practice questions here are very similar to those that appear in real exams. View Courses
Many students who study using our platform have reported that a large number of the practice questions here are very similar to those that appear in real exams. View Courses
Which of the following best describes a chemical change rather than a physical change?
Correct Answer: C. Iron reacting slowly with moisture to form reddish rust. Rusting is a chemical change because a new substance — iron oxide — is formed when iron reacts with oxygen and water in the environment. The atoms in iron (Fe) chemically combine with oxygen (O₂) and moisture to produce Fe₂O₃, a compound with entirely different properties from pure metallic iron. This process alters both the chemical composition and appearance of the metal. It is not reversible through simple physical means, such as heating or cooling, and requires a chemical reaction to undo (for example, through reduction).
Why the Other Options Are Incorrect:
A. Sugar crystals dissolving completely in warm water
This is a physical change because no new substance forms. The sugar molecules disperse evenly among the water molecules, but their structure remains the same. When the water evaporates, the sugar can recrystallize, proving that no chemical change occurred.
B. Water vapor condensing on the surface of a cold bottle
Condensation involves a change of state from gas to liquid, but the water molecules remain H₂O throughout the process. The molecular structure and chemical identity do not change, so it is purely a physical change.
D. Ice cubes melting into liquid at room temperature
Melting is another example of a phase change, where solid water becomes liquid water. The change affects only the physical state of the substance, not its molecular structure or composition.
Discover a range of courses designed to provide you with the knowledge and skills needed to excel in your chosen field.
You don’t need one month to study and pass your test.
With Prepsaret, it takes you a few days to grasp all the concepts needed to pass your exams