An interactive GCSE Chemistry lesson exploring the law of conservation of mass and balancing chemical equations (AQA 4.3.1.1). Animated particle models show how atoms rearrange during reactions without being created or destroyed, while a virtual mass experiment demonstrates conservation of mass. Students investigate coefficients and subscripts, balance equations using interactive atom counters, and develop their understanding through step-by-step worked examples, guided practice and exam-style questions. simopsis