Why can the balance reading change?
Why can the balance reading change?
Mass is always conserved in a chemical reaction. If a balance reading appears to change, the explanation is usually that a gas has entered or escaped from the container.
For example, when 10.0 g10.0\text{ g}10.0 g of magnesium burns completely in oxygen, it forms 16.6 g16.6\text{ g}16.6 g of magnesium oxide. The additional 6.6 g6.6\text{ g}6.6 g comes from oxygen entering the container.
Step-by-step lessons on AQA GCSE Chemistry 3.1.3 Mass changes when a reactant or product is a gas. Each one builds up to exam-style questions. Nail the core quantitative topics — moles, balancing equations and calculations — early on, since they underpin higher-tier questions across every paper and topic.