Classify each change as physical or chemical. a. Natural gas burns in a stove. b. The liquid propane in a gas grill evaporates because the valve was left open. c. The liquid propane in a gas grill burns in a flame. d. A bicycle frame rusts on repeated exposure to air and water.

Verified step by step guidance

1. Identify the type of change for each scenario by considering whether the chemical composition of the substance changes.
2. For part (a), consider if burning natural gas involves a change in chemical composition. Burning typically involves a chemical reaction with oxygen, producing new substances.
3. For part (b), determine if evaporation involves a change in the chemical identity of propane. Evaporation is a phase change from liquid to gas, which is a physical change.
4. For part (c), analyze if burning propane involves a chemical reaction. Like natural gas, burning propane involves a chemical reaction with oxygen, producing new substances.
5. For part (d), assess if rusting involves a change in the chemical composition of the bicycle frame. Rusting is a chemical reaction between iron and oxygen, forming iron oxide, a new substance.

Key Concepts

Physical Change

A physical change involves a transformation that does not alter the chemical composition of a substance. Examples include changes in state, such as melting or evaporation, where the substance remains the same at a molecular level. In the context of the question, the evaporation of liquid propane is a physical change, as it transitions from liquid to gas without changing its chemical structure.

Chemical Change

A chemical change results in the formation of one or more new substances with different chemical properties. This process often involves a reaction where bonds are broken and formed, leading to a change in composition. In the question, burning natural gas and propane are chemical changes, as they react with oxygen to produce new products like carbon dioxide and water.

Indicators of Chemical Change

Certain indicators can suggest that a chemical change has occurred, including color change, gas production, temperature change, and the formation of a precipitate. In the question, rusting of a bicycle frame is a chemical change indicated by the formation of rust, which is a new substance resulting from the reaction of iron with oxygen and moisture.