Work through the list without notes. If you cannot do a statement, follow its link, then come back. Guide = study guide; Practice = practice questions.
Understanding
- I can explain why breaking a bond needs energy and forming the same bond releases the same amount. (Guide: “Where the energy of a reaction comes from”; Practice Q1)
- I can define bond enthalpy and say why it is always a positive number. (Guide: “Bond enthalpy: an average value”)
- I can explain why a table value is an average, and why that makes the answer an estimate. (Guide; Practice Q4)
- I can explain why a fuel releases energy without saying that breaking bonds releases energy. (Practice Q7)
Calculation
- I can draw Lewis structures and list every bond broken and formed, multiplied by the coefficients. (Guide: “Counting bonds without mistakes”; Practice Q3, Q5)
- I can estimate ΔH as Σ(bonds broken) − Σ(bonds formed), with the correct sign. (Guide: Worked examples 1 and 2; Practice Q2)
- I can use the correct values for double and triple bonds, including O=O, N≡N and the C=O bonds in CO₂. (Practice Q3, Q5)
- I can cancel bonds that do not change and get the same answer. (Guide: Worked example 2)
- I can scale ΔH to a given mass of reactant. (Practice Q5)
- I can work backwards from a known ΔH to estimate one unknown bond enthalpy. (Guide: Worked example 3; Practice Q6)
Reasoning
- I can decide whether a reaction is exothermic or endothermic by comparing the energy needed to break bonds with the energy released forming bonds. (Guide: Worked example 1; Practice Q1, Q7)
- I can represent the method as a step diagram: up to separate atoms, then down to products. (Guide: Figure 1; Practice Q7)
- I can give two reasons a bond-enthalpy estimate differs from a measured value: averaging and non-gaseous substances. (Guide: “Why the answer is only an estimate”; Practice Q4, Q7)
All ticked? Move on to Topic 6.8, Enthalpy of Formation, or return to the course roadmap.