Question

Use the Bond Energies Table to estimate the enthalpy change in each of the following reactions. (Enter your answer to the nearest integer.) (a) CH4(g) C(g) 2 H2(g) 4.0 X kJ/mol (b) ICH3(g) + H20(g) H3COH(g) HI(g) 4.0 X kJ/mol HC CH(g)2 H2(g)H3C-CH 3 (g) (c) 4.0 X kJ/mol

Answer 1

CHi (9) C(g) + 2 H₂ (9) It takes enegy to break bonds, and enesgy is released when bands are formed ave tage band energies for ct 413 kolmo, H11, 436 kJ/mol Breaks y c-H bonds - 4 (413) = 1652 kJ Energy released forming a H₂ = 2(436) - 832 kJ since it to is released the value is regative DH = energy required to break bonds (positive o sign plus enesgy required to make bonds (negative sign DH= 1652-832= 820 kJ/mol b) I CH3(g) + H₂O(g) → H₃ COH(g) + HI(g) Average band energies for C-I = 240, 0-H=463. H-I = 299, (-0=358 in kJ/mol CH₃ I has 3c-H bonds and I-I 3(413 +1 (290) = 1479 ko Ho has 20-H bonds. 2 (463)=926 Total energy to break bonds= 14294926 - 2405 kJ

CH₃OH has 3 ch bonds, Ic-o bands, 14.o band 3/413 + 1 (358) + 1 (463) = 2060 kJ HI has 1H-I bond (299) Total energy released = 2060 +299=2359 kJ Total enthalpy a enesau required to break bonds (positive tenergy required to make bonds tives - (negat = 2405-2359 = 46 kJ/mol c) HCECH(g) + 2H₂(g) H3C-CH3 (9) Average boud energies for c-(2347, cac=839, c-t = 413, H-H=432 in kJ/mol HCECH has ICEC and 2 c H bands (839) + 2(413) = 1665 kJ 2H-H bands 2(432) = 864 kJ Total energy to break bonds 1665+864 2529 KJ H₃(-CH3 has one Ic-c band and six (at bands Total energy released= 347+ 6 (413) - 2826 KJ AH = energy required to break bands (postive) teneoy required to make bands (negative = 2529-2826= -296 kJ/mol