Use balanced equations to calculate reacting masses by proportion.
| English | Chinese |
|---|---|
| conservation of mass | 质量守恒 |
| mass ratio | 质量比 |
| closed system | 封闭体系 |
Try each question before opening its hint or answer. Use paper for calculations and diagrams.
Why can the mass decrease when a carbonate is heated in an open container?
Use the relationships above and check particle ratios and units.
CO₂ gas escapes; the measured system loses gas, but total mass is conserved.
2Mg + O₂ → 2MgO. Calculate the MgO mass from 12 g Mg in excess oxygen. Aᵣ: Mg = 24, O = 16.
Use the equation to find the reacting-mass ratio, then scale it.
48 g Mg → 80 g MgO; 12/48 × 80 = 20 g.
CaCO₃ → CaO + CO₂. Calculate the CaO mass from 25 g CaCO₃. Aᵣ: Ca = 40, C = 12, O = 16.
Find formula masses before comparing the masses of reactant and product.
100 g CaCO₃ → 56 g CaO; 25/100 × 56 = 14 g.
Use Lesson 3 in your worksheet for written practice. Your teacher will discuss those answers in class.
Predict the product mass. Reveal each step and explain why the equation ratio is not a mass ratio.
2Mg + O₂ → 2MgO
Assume excess oxygen and complete reaction. M(Mg) = 24 g mol⁻¹; M(MgO) = 40 g mol⁻¹.
Explain: why must we divide by one molar mass and multiply by another? Display values are rounded; calculations use full precision.