Calcium carbonate breaks down when it is heated strongly. Calcium oxide and carbon dioxide are made.
CaCO3(s)⇌CaO(s)+CO2(g) \mathrm{CaCO_{3}(s) \rightleftharpoons CaO(s) + CO_{2}(g)} CaCO3(s)⇌CaO(s)+CO2(g)Experiment 1: A student heats 10.00 g of calcium carbonate strongly in an open crucible. The student measures the mass of solid in the crucible every 2 minutes.
The table shows the results.
| Time (min) | Mass of solid in the crucible (g) |
|---|---|
| 0 | 10.00 |
| 2 | 9.02 |
| 4 | 7.95 |
| 6 | 6.90 |
| 8 | 6.08 |
| 10 | 5.60 |
| 12 | 5.60 |
| 14 | 5.60 |
Calculate the percentage of the starting mass that is lost in Experiment 1.
Percentage of mass lost = ...... %
The student thinks that at the end of Experiment 1 the solid is all calcium oxide.
Show that the student is correct.
Use the equation: mass of calcium oxide = mass of calcium carbonate × (Mr of CaO ÷ Mr of CaCO3\mathrm{CaCO_{3}}CaCO3)
Relative formula masses (Mr): CaCO3\mathrm{CaCO_{3}}CaCO3 = 100.1, CaO = 56.1
Explain why the mass of solid stops changing after 10 minutes in Experiment 1.
Experiment 2: The student heats 10.00 g of calcium carbonate to the same temperature in a sealed steel container.
The pressure of carbon dioxide in the container rises and then stays the same. Some calcium carbonate is still left in the container.
Explain why the pressure of carbon dioxide stops changing even though some calcium carbonate is left.
Use ideas about dynamic equilibrium.
Another student says:
"In Experiment 2 the reaction has stopped, because there are now equal amounts of calcium carbonate and calcium oxide."
Evaluate this statement.
47 exam-style questions on OCR GCSE Chemistry 5.3 Equilibria, covering 5.3.1 Reversible reactions and dynamic equilibrium and 5.3.2 Changing the position of equilibrium. Each one has a worked solution and a mark scheme showing where the marks go.