Which of the following demonstrates a chemical change?
Iron (Fe) reacting to water (H2O) and oxygen (O) to form iron oxide (Fe2O3)
dry ice vaporizing
sugar and water mixing to create sugar water
steam condensing on a mirror
Iron (Fe) reacting to water (H2O) and oxygen (O) to form iron oxide (Fe2O3) demonstrates a chemical change.
The correct answer is:
- Iron (Fe) reacting to water (H2O) and oxygen (O) to form iron oxide (Fe2O3)
This is a chemical change because new substances are formed as a result of the reaction. In this case, iron reacts with water and oxygen to form iron oxide.
The correct answer that demonstrates a chemical change is:
Iron (Fe) reacting to water (H2O) and oxygen (O) to form iron oxide (Fe2O3).
To understand why this is a chemical change, we need to know what chemical changes are. A chemical change occurs when one or more substances are transformed into new substances with different properties.
In this case, iron (Fe) is reacting with water (H2O) and oxygen (O) to form iron oxide (Fe2O3), also known as rust. The iron atoms in the iron strip are combining with oxygen atoms from the air and hydrogen atoms from water to create a new compound, iron oxide. This is an example of a chemical change because new substances with different properties are formed.
To identify chemical changes, you should look for the formation of new substances, changes in color, the release or absorption of energy (such as heat or light), the production of gas, or the formation of a solid (precipitate).
Now let's discuss the other options:
- Dry ice vaporizing: This is an example of a physical change. Dry ice is the solid form of carbon dioxide (CO2) and when it undergoes vaporization, it directly changes from a solid to a gas. This does not involve the formation of new substances, but rather a change in the physical state of the existing substance.
- Sugar and water mixing to create sugar water: This is also a physical change. When sugar is mixed with water, it dissolves and forms a homogeneous mixture called sugar water. No new substances are formed; it is simply a combination of sugar and water at a molecular level.
- Steam condensing on a mirror: This is another physical change. When water vapor (steam) comes into contact with a cold surface like a mirror, it loses energy and condenses back into liquid water. This change in state does not involve the formation of new substances, but rather a transformation from gas to liquid.
In summary, the only option that demonstrates a chemical change is the reaction of iron with water and oxygen to form iron oxide.