How can we say that burning a candle is a chemical change, but the glowing of a bulb is a physical change?
The correct answer and explanation is:
Correct Answer:
Burning a candle is a chemical change, while the glowing of a bulb is a physical change because burning involves the formation of new substances, whereas the bulb simply converts electrical energy into light and heat without changing the material composition.
Explanation (300 words, no em-dashes or “we”):
A chemical change is a process in which substances react to form one or more new substances with different chemical properties. In contrast, a physical change is one where the physical properties of a substance may change, such as its state or appearance, but its chemical composition remains the same.
When a candle burns, it undergoes a chemical change. The wax of the candle, which is made up of hydrocarbons, reacts with oxygen in the air during combustion. This reaction produces carbon dioxide, water vapor, heat, and light. The original wax molecules are chemically broken down and transformed into new substances. These new products have different chemical structures and properties from the original wax. This transformation is irreversible under normal conditions, and the candle wax that has been burned cannot be recovered.
On the other hand, the glowing of a bulb involves a physical change. In an incandescent bulb, electric current passes through a tungsten filament. The electrical energy heats the filament to a very high temperature, causing it to glow and emit light. Although the filament becomes extremely hot and emits both light and heat, there is no change in the chemical composition of the tungsten filament or the gas inside the bulb. No new substances are formed in the process. When the electricity is turned off, the filament simply cools down and returns to its original state.
Therefore, the burning of a candle qualifies as a chemical change due to the creation of new materials, while the glowing of a bulb is a physical change because the materials involved do not change chemically.