IGCSE Chemistry 0620/21/O/N/21 Q11

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11 Chlorine reacts with ethane to produce chloroethane and hydrogen chloride.

The reaction is exothermic.

The bond energies are shown in the table.
bond         bond energy in kJ / mol
C–Cl          +340
C–C           +350
C–H          +410
Cl–Cl        +240
H–Cl         +430

What is the energy change for the reaction?

A –1420 kJ /mol
B –120 kJ /mol
C +120 kJ / mol
D +1420 kJ / mol

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Answer ( 1 )

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    2022-05-11T15:13:10+08:00

    Energy of bond breaking – Energy of bond formation = Energy Change

    Bond breaking = 410 (C-H) + 240 (Cl-Cl) = 650 kJ/mol

    Bond formation = 340 (C-Cl) + 430 (H-Cl) = 770 kJ/mol

    Energy change = 650 – 770 = -120 kJ/mol

    Ans: B -120 kJ/mol

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