Rates, Energy & Reaction Experiments: Endothermic Vs Exothermic Experimental Evidence (Copy)
Rates, Energy & Reaction Experiments
Endothermic Vs Exothermic Experimental Evidence
Purpose in ATP
- Distinguish reactions based on energy transfer
- Examiners test:
- Observation of temperature changes
- Interpretation of energy flow
- Linking evidence to reaction type
Core Examiner Rule
- Always report:
- Observation (temperature rises/falls)
- Conclusion (exothermic/endothermic)
- Units must be included for temperature (°C)
- Logical connection between observation and energy transfer is required
1. Exothermic Reactions
Experimental Evidence
- Observation: Temperature of surroundings increases
- Example experiments:
- Neutralisation: HCl + NaOH → NaCl + H₂O
- Combustion reactions: C + O₂ → CO₂
- Rate measurement: Can also observe faster reaction at higher temperature due to energy release
Examiner Notes
- Must link temperature rise to energy released to surroundings
- ΔH is negative (products lower energy than reactants)
- Optional: Can show graph with upward trend in temperature vs time
2. Endothermic Reactions
Experimental Evidence
- Observation: Temperature of surroundings decreases
- Example experiments:
- Dissolving ammonium chloride in water
- Photosynthesis (plant-based reactions, demonstration)
- Rate may decrease if temperature lowers surrounding medium
Examiner Notes
- Must link temperature fall to energy absorbed from surroundings
- ΔH is positive (products higher energy than reactants)
- Optional: Graph shows downward trend in temperature vs time
Written and Compiled By Sir Hunain Zia, World Record Holder With 154 Total A Grades, 7 Distinctions and 11 World Records For Educate A Change O Level And IGCSE Chemistry Full Scale Course
Step 3: Recording Temperature Changes
- Use thermometer or temperature probe
- Record initial and final temperature
- Calculate ΔT = Final − Initial
- Positive ΔT → Exothermic
- Negative ΔT → Endothermic
Step 4: Representing Experimental Evidence
- Tabular format:
| Reaction | Observation | ΔT (°C) | Energy Type |
|---|---|---|---|
| HCl + NaOH | Temperature rises | +5 | Exothermic |
| NH₄Cl + H₂O | Temperature falls | −2 | Endothermic |
- Graphical evidence:
- Exothermic: upward slope
- Endothermic: downward slope
Step 5: Examiner-Traps
- Failing to include units for temperature
- Reporting reaction type without observation
- Confusing temperature fall with exothermic
- Forgetting ΔT calculation
High-Yield ATP Tips
- Measure temperature accurately
- Include units (°C)
- Note increase or decrease in surroundings
- Relate observation to energy absorbed or released
- Use table or graph for clarity
- Always conclude exothermic or endothermic
Core Scientific Principle
- Exothermic: Energy released → surroundings warm → ΔH negative
- Endothermic: Energy absorbed → surroundings cool → ΔH positive
- Observation of temperature change provides practical evidence of reaction energetics
- Correctly recording and interpreting ΔT:
- Guarantees maximum ATP marks for energy reaction experiments
Written and Compiled By Sir Hunain Zia, World Record Holder With 154 Total A Grades, 7 Distinctions and 11 World Records For Educate A Change O Level And IGCSE Chemistry Full Scale Course