VIRTUAL EXPERIMENT · REACTION RATES
Watch the cross. Time the change. Discover the effect of temperature.
01 / OBSERVE FROM ABOVE
The cross is on the tile, underneath the beaker. Look straight down through the solution.
04 / RECORD & COMPARE
Use the same visual endpoint for every trial. Repeat a temperature to compare readings.
| Trial | Temperature / °C | Time, t / s | 1/t / s⁻¹ | Observation | Remove |
|---|---|---|---|---|---|
| Complete a trial to record your first result. | |||||
Early stops are marked and excluded from the graph. A late stop gives a smaller 1/t than stopping at the endpoint.
Your valid readings will appear here. No results are filled in for you.
WHAT BLANKETS THE CROSS?
A fine, pale-yellow solid forms in the liquid and scatters light. The cross is still on the tile; you can no longer see it through the mixture.
S₂O₃²⁻(aq) + 2H⁺(aq)
→ S(s) + SO₂(g) + H₂O(l)
It is the sulphur precipitate, not the sulphur dioxide gas, that obscures the cross.
WHY USE 1/TIME?
With the same mixture and viewing conditions, about the same amount of sulphur is needed to hide the cross. Producing it in less time means a faster reaction.
Relative rate ∝ 1 / time
1/t is a comparative rate measure here, not a concentration change in mol dm⁻³ s⁻¹.
EXPLAIN USING COLLISIONS
At higher temperature, particles move faster and collide more often. More collisions also have enough energy to react.
With correct orientation and enough energy, more collisions are effective each second, so sulphur forms faster.
Explore collision theory →Compare 1/t at 25, 35, 45 and 55 °C. The rate increases as temperature rises, but it is not directly proportional to temperature in °C.
For a directly proportional relationship, doubling the temperature value would double 1/t, and the graph would be a straight line through the origin.
Based on Experiment 37.3, “Investigating the effect of temperature on rate of reaction”, in the supplied HKDSE New Chemistry — A Modern View worksheet (Aristo Educational Press). Volumes, stock concentrations and the 35, 45 and 55 °C trials follow that worksheet. Room temperature is represented by 25 °C.
The mixture temperature is held constant during each run. The illustration uses a gradual, stylised increase in cloudiness. The chosen model endpoint is 80 × 2−(T−25)/10 seconds; this illustrative doubling of rate per 10 °C is not a universal rule. These times are invented for learning, not measured results or predictions for the worksheet’s reagents. A visual endpoint is subjective in a real experiment.
For a real laboratory experiment, follow your teacher’s instructions: wear eye protection and gloves, handle acid and hot apparatus carefully, and use suitable ventilation because sulphur dioxide is harmful to inhale. Clean and dry the beaker between trials and use the designated chemical-waste containers.
Further reading: Royal Society of Chemistry: temperature and reaction rate.