In basic physical chemistry, which of the following processes is a chemical change rather than a purely physical change?

Introduction / Context:
Distinguishing between physical and chemical changes is one of the first important skills learned in chemistry. A physical change alters the form or state of a substance without changing its chemical composition, while a chemical change results in the formation of new substances with different properties. This question asks you to identify which listed process is a true chemical change. Understanding this difference helps in analysing everyday phenomena and laboratory reactions.

Given Data / Assumptions:
- The processes listed are burning gasoline, boiling water, evaporating water, and melting ice. - We must decide which of these is a chemical change. - We assume normal conditions and typical definitions used in school level chemistry.

Concept / Approach:
A chemical change involves a chemical reaction where bonds are broken and new bonds are formed, producing new substances. Combustion is a classic example. In contrast, physical changes such as melting, boiling, or evaporation involve changes of state, but the chemical identity of the substance remains the same. When water changes from ice to liquid to vapour, it is still H2O. When gasoline burns in air, however, hydrocarbons react with oxygen to form carbon dioxide, water, and other products, completely changing the chemical composition.

Step-by-Step Solution:
Step 1: Examine burning gasoline. This process involves hydrocarbons reacting with oxygen in a combustion reaction that produces carbon dioxide, water vapour, and heat. New chemical substances are formed. Step 2: Examine boiling water. Water changes from liquid to gas, but the molecules remain H2O, so this is a physical change. Step 3: Examine evaporating water. Evaporation is another liquid to gas phase change with no change in chemical identity, so this is also a physical change. Step 4: Examine melting ice. Ice turning into liquid water is a solid to liquid phase change, again involving the same H2O molecules. Step 5: Conclude that burning gasoline is the only option in which new substances are formed, so it is the chemical change.

Verification / Alternative check:
Another way to verify is to ask whether the original substance can be recovered by simple physical means. Melted ice can be refrozen, and water vapour can be condensed back to liquid water, demonstrating that these are reversible physical processes. In contrast, once gasoline burns, you cannot easily recover the original hydrocarbons from the exhaust gases and ash because the molecules have been chemically transformed. This irreversibility and formation of new substances confirm that burning gasoline is a chemical change.

Why Other Options Are Wrong:
Option B (Boiling water) is a physical change because it only changes the state from liquid to gas without altering the chemical composition of water. Option C (Evaporating water) is also a physical change, representing the same liquid to gas transition at the surface. Option D (Melting ice) is a physical change where solid water becomes liquid water, with the molecules remaining the same.

Common Pitfalls:
Students sometimes confuse the presence of heat with a chemical change and assume any process involving heating must be chemical. However, many phase changes such as melting and boiling require heat but remain purely physical. Another pitfall is not focusing on whether new substances with new properties are formed. To classify changes correctly, always ask whether the chemical identity of the substance has changed, not just its state or appearance.

Final Answer:
The correct answer is: Burning gasoline.