To compare conditions, use the numbers in the question. Convert them to a rate if needed, state which condition is best among those tested, and explain why with a chemistry idea.
This lesson is part of energy evidence and industrial chemistry reasoning. The explanation idea comes from collision theory.
What is the method?
Work through these steps and write each as a separate line.
- List the conditions and the measured values.
- Convert times into rates using rate = 1 ÷ time where needed.
- Compare the rates and identify the highest.
- Write claim, evidence and reason, and state the limit of the data.
Worked example: three temperatures
An original class experiment measures the time for the same reaction to finish at three temperatures.
| Temperature (°C) | Time to finish (s) | Rate = 1 ÷ time (per s) |
|---|---|---|
| 30 | 120 | 0.0083 |
| 50 | 45 | 0.022 |
| 70 | 20 | 0.050 |
Claim: among the three temperatures tested, 70 °C gives the highest rate.
Evidence: the reaction finishes in 20 s at 70 °C, compared with 45 s at 50 °C and 120 s at 30 °C. The rate at 70 °C is 0.050 per second, which is six times the rate at 30 °C (0.050 ÷ 0.0083 is about 6).
Reason: at a higher temperature, particles move faster and a larger fraction have energy at or above the activation energy, so the frequency of effective collisions rises.
Limit: only three temperatures were tested, so the data do not show what happens above 70 °C.
The mistake that costs marks
The common slip is to write an unsourced claim such as “factories use high temperatures, so 70 °C is best”. This adds a statement that the data does not support, and it gives no evidence.
| Answer | Verdict |
|---|---|
| “Industry uses high temperatures, so 70 °C is best.” | Unsupported claim with no data |
| “70 °C is fastest: 20 s against 120 s at 30 °C, because more particles reach the activation energy.” | Data, reason and link to theory |
Another slip is to choose the condition with the shortest time without writing the numbers. Always quote two values.
Check yourself
A different experiment gives times of 90 s at 25 °C and 30 s at 45 °C. Convert to rates, compare them, and state one limit of the data.
Answer
Rates: 1 ÷ 90 = 0.011 per s at 25 °C and 1 ÷ 30 = 0.033 per s at 45 °C.
The rate at 45 °C is three times the rate at 25 °C, because 0.033 ÷ 0.011 = 3.
Limit: only two temperatures were tested, so the data show the trend between 25 °C and 45 °C, not what happens outside that range or at temperatures in between.
What to study next
Return to the energy evidence overview to choose the next skill, or practise the structure with the claim evidence and explanation revision desk.
If you want a teacher to review your answers to data questions, see online one-to-one Chemistry tuition. The mistake log and paper-error review tool helps you track which slips recur.