Bromoalkanes are used widely in industry, although there is increasing concern about their environmental impact. Fig. 4.1 shows a reaction scheme involving 1,2-dibromoethane. Fig. 4.1 The enthalpy change of reaction $$$1, \Delta H_{r}=-90.0 \mathrm{~kJ} \mathrm{~mol}^{-1}$$$. The enthalpy change of formation of ethene, $$$\Delta H_{f}=+52.2 \mathrm{~kJ} \mathrm{~mol}^{-1}$$$. Calculate the enthalpy change of formation of 1,2-dibromoethane. $$\[ \Delta H_{\mathrm{f}} \text { of 1,2-dibromoethane = } \]$$ .......................... $$$\mathrm{kJmol}^{-1}$$$

Chemistry

IGCSE&ALevel

CAIE

Exam No：9701_w24_qp_22 Year：2024 Question No：4(b)

Answer:

Knowledge points:

5.1.1 understand that chemical reactions are accompanied by enthalpy changes and these changes can be exothermic (ΔH is negative) or endothermic (ΔH is positive)

5.1.2 construct and interpret a reaction pathway diagram, in terms of the enthalpy change of the reaction and of the activation energy

5.1.3.1 standard conditions (this syllabus assumes that these are 298 K and 101 kPa) shown by

5.1.3.2 enthalpy change with particular reference to: reaction, , combustion, , neutralisation,

5.1.4 understand that energy transfers occur during chemical reactions because of the breaking and making of chemical bonds

5.1.5 use bond energies (ΔH positive, i.e. bond breaking) to calculate enthalpy change of reaction

5.1.6 understand that some bond energies are exact and some bond energies are averages

5.1.7 calculate enthalpy changes from appropriate experimental results, including the use of the relationships q = mcΔT and ΔH = –mcΔT/n

Answer:

Knowledge points:

Solution:

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