Chemical properties refer to how a substance interacts with other substances during a chemical reaction. These properties can include reactivity, flammability, and acidity. For example, when sodium reacts with water, it produces sodium hydroxide and hydrogen gas, demonstrating its chemical reactivity. Physical properties, on the other hand, describe the characteristics of a substance that can be observed without changing its chemical identity. These include color, melting point, boiling point, and density. For instance, the melting point of ice is 0 degrees Celsius, which is a physical property that can be measured without altering the ice's chemical structure.