Which of the following processes represents a chemical change?
Heating solid iodine crystals in a sealed tube to form a purple vapor.
Dissolving anhydrous calcium chloride in water, resulting in a temperature rise of the solution.
Heating a mixture of iron powder and sulfur powder until a red glow spreads through the mixture, forming a dark, non-magnetic solid.
Isolating liquid oxygen from liquid air via fractional distillation.
55 exam-style questions on OCR GCSE Chemistry Introducing chemical reactions. Each one has a worked solution and a mark scheme showing where the marks go.