Document page
chemistry igcse acapprinted 43 · PDF 43
145 pagesrevision 46934
printed 43 · PDF 43
Page image rendered from the stored file at 110 dpi; it sharpens as you zoom. Outlines are placed from each region’s stored position on the page (612 × 792 pt).
readable
Source of this text: embedded text layer. The better of the embedded text and OCR is kept.
43
Bond Energy Calculations
• During bond energy calculations, always remember:
∆H=Energy absorbed in Bond breaking-Energy released in Bond formation
OR
∆H=Reactants-Products
Q. The chemical equation for this reaction can be represented as shown.
The energy change for the reaction is –180kJ/mol.
Use the bond energies in the table to calculate the bond energy of a C–Cl bond, in kJ / mol.
bond C-H
C=H Cl-Cl C-C
bond energy in kJ/mol 410
610
240
350
Use the following steps:
Step 1 Calculate the energy needed to break bonds.
= 4(C-H) + (C=C) + (Cl-Cl)
= 4(410) + (610) + (240)
= 1640 + 850
= +2490 kJ
Step 2 Use your answer in Step 1 and the energy change for the reaction to determine the energy
released when bonds are formed.
2490 – x = -180
x = 2490 + 180
x = 2670 kJ
Step 3 Use your answer in Step 2 and bond energy values to determine the energy of a C–Cl bond.
2(C-Cl) + (C-C) + 4(C-H) = 2670
2 (C-Cl) + (350) + 4(410) = 2670