Why the balance reading changes
Why the balance reading changes
Mass is always conserved in a chemical reaction. If the balance reading appears to change, the explanation is that a gas has entered or left the container being weighed. In a sealed system, gases cannot enter or escape, so the total mass remains constant. For example, when calcium carbonate decomposes in a sealed container, both products, calcium oxide and carbon dioxide, remain inside: CaCO3→CaO+CO2\text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2CaCO3→CaO+CO2.
Step-by-step lessons covering AQA GCSE Chemistry 3.1.3 Mass changes when a reactant or product is a gas for Foundation and Higher tier. Each lesson works through exam-style questions in Paper 1 and Paper 2 format. Nail the core quantitative topics — moles, balancing equations and calculations — early on, since they underpin higher-tier questions across every paper and topic.
