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Edexcel IAL Chemistry 6.9 Bond and mean bond enthalpy

Draw or inspect all reactant and product bonds, calculate bonds broken minus bonds formed and distinguish a specific bond value from a mean across compounds.

Syllabus
First assessment 2019
Course
Chemistry YCH11
Level
AS

Exam points

  • Calculate reaction enthalpy as total bonds broken minus total bonds formed.
  • Distinguish a specific bond enthalpy from a mean value averaged across compounds.
  • Explain disagreement with measured enthalpy through averaging and gas-phase assumptions.

6.9—The terms ‘bond enthalpy’ and ‘mean bond enthalpy’ question 1

[Maximum number: 1]

Consider the bond enthalpy values given in the table.

The equation for the reaction between nitrogen and hydrogen is shown.
N₂(g) + 3H₂(g) → 2NH₃(g)

What is the enthalpy change, in kJ mol⁻¹, for this reaction?

Figure for Question 6.9—The terms ‘bond enthalpy’ and ‘mean bond enthalpy’ question 1 — Edexcel A-Level Chemistry AS
A

+1080

B

+852

C

−93

D

−529

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