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Enthalpy changes

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Question 11

Standard enthalpy changes can be used to determine unknown bond strengths in covalent molecules.

Consider the gas-phase synthesis of nitrogen trifluoride:

N2(g)+3F2(g)→2NF3(g)ΔrH=−234 kJ mol−1 \text{N}_2(\text{g}) + 3\text{F}_2(\text{g}) \rightarrow 2\text{NF}_3(\text{g}) \quad \Delta_r H = -234 \text{ kJ mol}^{-1} N2​(g)+3F2​(g)→2NF3​(g)Δr​H=−234 kJ mol−1

Using the following bond enthalpies, what is the mean bond enthalpy, in kJ mol−1\text{kJ mol}^{-1}kJ mol−1, of the N−F\text{N}-\text{F}N−F bond?

  • N≡N=+945 kJ mol−1\text{N}\equiv\text{N} = +945 \text{ kJ mol}^{-1}N≡N=+945 kJ mol−1
  • F−F=+159 kJ mol−1\text{F}-\text{F} = +159 \text{ kJ mol}^{-1}F−F=+159 kJ mol−1
A

−276-276−276

B

+198+198+198

C

+276+276+276

D

+552+552+552

Markscheme

Enthalpy changes Questions

  1. A Level
  2. /Chemistry
  3. /Enthalpy changes

31 exam-style questions on OCR A A Level Chemistry Enthalpy changes. Each one has a worked solution and a mark scheme showing where the marks go.

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