A sealed reaction vessel containing methane and oxygen is placed on a balance. The mixture reacts to form carbon dioxide gas and water vapour. The vessel remains sealed.
CH4+2O2→CO2+2H2O\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O}CH4+2O2→CO2+2H2O
Which statement explains what happens to the balance reading?
The reading decreases because carbon dioxide gas and water vapour are formed.
The reading stays the same because no substance can enter or leave the vessel.
The reading stays the same because the reactants and products are gases with no mass.
The reading increases because oxygen becomes part of carbon dioxide and water vapour.
95 exam-style questions on AQA GCSE Chemistry 3.1 Chemical measurements, conservation of mass and the quantitative interpretation of chemical equations, covering 3.1.1 Conservation of mass and balanced chemical equations, 3.1.2 Relative formula mass, 3.1.3 Mass changes when a reactant or product is a gas, and 3.1.4 Chemical measurements. Each one has a worked solution and a mark scheme showing where the marks go.