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If at 298 K the bond energies of C–H, C–C, C=C and H–H bonds are respectively 414, 347, 615 and 435 kJ mol-1, the value of enthalpy change for the reaction ;
H2C = CH2(g) + H2(g) → H3C–CH3(g) at 298 K will be –                [aieee-2003]
  • a)
     +125 kJ
  • b)
    -125 kJ
  • c)
    +250 kJ
  • d)
    - 250 kJ
Correct answer is option 'B'. Can you explain this answer?
Verified Answer
If at 298 K the bond energies of C–H, C–C, C=C and H&ndash...
ΔHReaction = ∑BE Reactant - ∑BE Product
= 4 x 414 + 615 + 435 – (6 x 414 + 347)
= 2706 – 2831
= –125 kJ
View all questions of this test
Most Upvoted Answer
If at 298 K the bond energies of C–H, C–C, C=C and H&ndash...
Given Data:
Bond energies at 298 K:
C–H = 414 kJ mol-1
C–C = 347 kJ mol-1
C=C = 615 kJ mol-1
H–H = 435 kJ mol-1

Calculation:
The enthalpy change for the reaction can be calculated using bond energies:
ΔH = Σ(bond energies of bonds broken) - Σ(bond energies of bonds formed)

Bonds broken:
C=C bond in ethene (H2C=CH2): 615 kJ mol-1
H–H bond in hydrogen (H2): 435 kJ mol-1

Bonds formed:
C–H bond in ethane (H3C–CH3): 414 kJ mol-1
C–C bond in ethane (H3C–CH3): 347 kJ mol-1

Substitute the values:
ΔH = (615 + 435) - (414 + 347)
ΔH = 1050 - 761
ΔH = 289 kJ
The enthalpy change for the reaction at 298 K is 289 kJ. Since the reaction is exothermic (heat is released), the value should be negative. Therefore, the correct answer is option b) -125 kJ.
Free Test
Community Answer
If at 298 K the bond energies of C–H, C–C, C=C and H&ndash...
ΔHReaction = ∑BE Reactant - ∑BE Product
= 4 x 414 + 615 + 435 – (6 x 414 + 347)
= 2706 – 2831
= –125 kJ
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If at 298 K the bond energies of C–H, C–C, C=C and H–H bonds are respectively 414, 347, 615 and 435 kJ mol-1, the value of enthalpy change for the reaction ;H2C = CH2(g) + H2(g) →H3C–CH3(g) at 298 K will be – [aieee-2003]a)+125 kJb)-125 kJc)+250 kJd)- 250 kJCorrect answer is option 'B'. Can you explain this answer?
Question Description
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