Question

Joe watches a candle burn. What chemical change does he observe? (Heat and light are produced; the candle wax turns liquid as it burns; the heat melts the candle wax)

Answer 1

As Joe watches the candle burn, he observes a chemical change primarily because the wax (a hydrocarbon) reacts with oxygen in the air to produce carbon dioxide and water vapor. This process releases heat and light, which are forms of energy.

While the candle wax melting into liquid is a physical change, the act of combustion (burning) that produces heat and light, along with the transformation of the wax into gaseous products (carbon dioxide and water vapor), is a chemical change. Therefore, the most significant chemical change Joe observes is the combustion of the wax, leading to the production of new substances (carbon dioxide and water) and the release of energy in the form of heat and light.