Measuring gas volume over time – average and instantaneous rate of reaction
ChemistryKinetics & EquilibriumAges 15–16Virtual lab
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Kinetics & Equilibrium
Virtual experiment: add CaCO₃ (lumps or powder) or Zn to 50 mL of HCl solution; the CO₂ or H₂ produced pushes out the plunger of a gas syringe while a stopwatch runs and the V(t) graph is plotted. Students drag two time markers to find the average rate (secant) and the instantaneous rate (tangent), then change concentration, temperature and surface area and compare the runs on the same graph.
Lesson: Rate of reaction – average rate and factors affecting the rate
What it shows
A rate of reaction can be followed by collecting a gaseous product: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂ or Zn + 2HCl → ZnCl₂ + H₂. The gradient of the volume–time graph is the rate. It is steepest at the start, when the acid concentration and exposed surface are greatest, and falls to zero once the limiting reactant is used up. In the model the rate is proportional to [H⁺] and to surface area and doubles for every 10 °C rise, while the final gas volume depends only on the amount of limiting reactant.
How to use
Choose the Solid, the Form of the solid, the Mass of solid, the HCl concentration and the Temperature, then press Run and watch the gas syringe fill. Drag the markers t₁ and t₂ on the graph to get the average rate from the secant and the instantaneous rate from the tangent. Press New run, change just one factor, and compare the curves and the results table; Clear graph starts a fresh set.
Parameters you can change
- Solid CaCO₃ (limestone) – collect CO₂, Zn – collect H₂
- Form of the solid Lumps (small surface area), Powder (large surface area)
- Mass of solid 0.1–0.5 g
- HCl concentration (50 mL) 0.2–2 M
- Temperature 15–55 °C
Questions to explore
- Why is the V(t) graph steepest at the start and then gradually levels off?
- Do lumps and powder of the same mass give the same final volume of gas, and why?
- How does the time to collect half the final volume change when the temperature rises by 10 °C?
Teaching ideas
All guides- Interactive Chemistry Lesson Ideas with SimulationsInteractive chemistry lesson ideas for grades 6–12: ten simulation activities on atoms, bonding, gases, pH, rates, equilibrium and electrochemistry.
- Rates of Reaction Virtual Lab: Acid Concentration and GasA rates of reaction virtual lab for the GCSE gas-collection practical: react marble chips with acid, record gas volume over time and compare concentrations.
- Disappearing Cross Virtual Lab: Concentration and RateA disappearing cross virtual lab for the GCSE rates practical: time sodium thiosulfate and acid, plot 1/t against concentration and test temperature.
