Chemistry Year 11 - Module 4 - Lesson 10
Hess's Law Applied — Heat of Combustion & Consolidation
1. Key Ideas
Engineers designing a car to run on ethanol vs octane need to know which fuel delivers more energy — per mole, per gram, and per litre. They calculate these values entirely on paper using the three methods you have built across Lessons 6–9. This lesson puts them all together: when to use bond energies, when to use ΔH° f values, and when Hess's Law is the only option.
- Energy per gram = |ΔH c | ÷ M (kJ g⁻¹) — the mass-based fuel comparison
- Why the three ΔH calculation methods are equivalent when applied to the same reaction
2. Success Criteria
By the end, you should be able to:
- Energy per gram = |ΔH c | ÷ M (kJ g⁻¹) — the mass-based fuel comparison
- Bond energy method → approximate; ΔH°f method → more accurate; Hess's Law → depends on data quality
- ΔH°f method and Hess's Law combustion cycle are mathematically equivalent
3. Key Terms
4. Activity: Build the Lesson Map
Use the lesson to complete the table. Keep answers brief but specific.
| Prompt | Your answer |
|---|---|
| Main concept | |
| Important example | |
| Common mistake to avoid | |
| How this links to the next lesson |
5. Short Answer Questions
1. Explain this lesson goal in your own words: "Energy per gram = |ΔH c | ÷ M (kJ g⁻¹) — the mass-based fuel comparison". Use one specific example from the lesson.
2. Apply this idea to a new example: "Bond energy method → approximate; ΔH°f method → more accurate; Hess's Law → depends on data quality". Show your reasoning clearly.
3. Analyse why this idea matters for understanding Hess's Law Applied — Heat of Combustion & Consolidation: "ΔH°f method and Hess's Law combustion cycle are mathematically equivalent".
6. Extend: Apply the Idea
A student gives a memorised answer about Hess's Law Applied — Heat of Combustion & Consolidation but does not use evidence or reasoning.
Improve the answer by writing a stronger response that uses accurate terminology, a relevant example and a clear explanation.
7. Multiple Choice
1. What is the best first step when answering a question about Hess's Law Applied — Heat of Combustion & Consolidation?
A. Identify the key concept being tested
B. Write every fact from memory
C. Ignore the command word
D. Skip examples and evidence
2. Which answer would show stronger understanding of Hess's Law Applied — Heat of Combustion & Consolidation?
A. An answer with accurate terms and reasoning
B. A copied definition only
C. A single-word response
D. An answer with no example
3. What should you do if a question asks you to explain?
A. Link the idea to a reason or cause
B. List unrelated facts
C. Only draw a diagram
D. Write the shortest possible answer
8. Success Criteria Proof
Finish with evidence that you can do each success criterion.