X and Y represent two elements. A solid compound has the formula X2Y5\text{X}_2\text{Y}_5X2Y5. When the compound is heated, it decomposes to form solid X and gas Y2\text{Y}_2Y2.
A student heats a sample of the compound in an open container until it has fully decomposed. No solid is lost from the container. The balance readings are shown in the table.
| Stage | Balance reading in g |
|---|---|
| Before heating | 37.62 |
| After heating and cooling | 35.94 |
Balance this equation.
X2Y5→X+Y2\text{X}_2\text{Y}_5 \rightarrow \text{X} + \text{Y}_2X2Y5→X+Y2
Explain why the balance reading decreased.
Calculate the mass of Y2\text{Y}_2Y2 produced.
The same reaction is carried out in a sealed reaction vessel. The balance reading before heating is 48.35 g. The vessel is allowed to cool before the final reading is taken.
Explain what the final balance reading will be.
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.