STUDENT SPACE · TOPIC 3
Conservation and reacting masses
Use balanced equations to calculate reacting masses by proportion.
The essentials
- No atoms are created or destroyed in a chemical reaction.
- In a closed system, total mass before = total mass after.
- If a gas escapes, the mass on a balance can decrease.
- The gas still has mass. Include it when accounting for all products.
Key vocabulary
| English | Chinese |
|---|---|
| conservation of mass | 质量守恒 |
| mass ratio | 质量比 |
| closed system | 封闭体系 |
Quick practice
Why can the mass decrease when a carbonate is heated in an open container?
Need a hint?
Use the relationships above and check particle ratios and units.
Check your reasoning after trying
CO₂ gas escapes; the measured system loses gas, but total mass is conserved.
Use Lesson 3 in your worksheet for written practice. Your teacher will discuss those answers in class.