A friend tells you "Because composition does not change during a physical change, the appearance of a substance does not change." Is your friend correct? Explain?
No completely. A physical change is not accompanied by a change in composition, unlike a chemical change, where chemical composition changes. That part is correct. However, appearance may not have anything to do with the chemical composition change. In other words, the appearance of a substance can change without a change in its chemical composition. Think about melting a metal or candle wax. As we progressively heat the substance (metal or candle wax), it starts melting. However, this does not mean that the chemical composition has changed. Candle wax will still be candle wax and metal (say iron) will still be the same metal. Yet we will get a different appearance of molten material as compared to the solid material. Think of ice and liquid water. In all these case, the energy of constituent molecules or atoms have increased, yet the material remains the same, only the phase changes. Thus, physical changes can bring about a change in appearance of a material.
Hope this helps.