Question 44
GCE_MODEL_QUESTIONS_VOL1
•
2021
•
CHEMISTRY
•
objective
Using the average bond enthalpies: Cl-Cl 242 kJ·mol\(^{-1}\), F-F 158 kJ·mol\(^{-1}\), Cl-F 255 kJ·mol\(^{-1}\), calculate the standard enthalpy change for the reaction \(\mathrm{Cl_2(g) + 3F_2(g) \rightarrow 2ClF_3(g)}\). Then, given that the standard enthalpy of formation of \(\mathrm{ClF_3(g)}\) is -58 kJ·mol\(^{-1}\), comment on the exothermicity predicted by the bond‑enthalpy method.
Answer Options
A.
\(\Delta H_{rxn}\approx -950\ \text{kJ}\) (bond‑energy estimate) - the reaction is predicted to be very exothermic, compared with the formation‑enthalpy value of \(-116\ \text{kJ}\), indicating an even larger over‑prediction.
B.
\(\Delta H_{rxn}\approx -400\ \text{kJ}\) (bond‑energy estimate) - the reaction is predicted to be mildly exothermic, whereas the formation‑enthalpy data give \(-116\ \text{kJ}\), suggesting the bond‑energy method under‑estimates the release.
C.
\(\Delta H_{rxn}\approx -650\ \text{kJ}\) (bond‑energy estimate) - the reaction is predicted to be moderately exothermic, while the formation‑enthalpy data give \(-116\ \text{kJ}\), showing the bond‑energy method still over‑estimates the release.
Correct Answer
D.
\(\Delta H_{rxn}\approx -814\ \text{kJ}\) (bond‑energy estimate) - the reaction is predicted to be strongly exothermic, whereas the formation‑enthalpy data give only \(-116\ \text{kJ}\), indicating the bond‑energy method over‑estimates the release.
Correct Answer
D
Correct Option:
\(\Delta H_{rxn}\approx -814\ \text{kJ}\) (bond‑energy estimate) - the reaction is predicted to be strongly exothermic, whereas the formation‑enthalpy data give only \(-116\ \text{kJ}\), indicating the bond‑energy method over‑estimates the release.
About This Question
This is
Gce Model Questions Vol1
2021
Chemistry
Question 44.
It is one of the
objective
questions from the
2021
Gce Model Questions Vol1
Chemistry
examination.
Difficulty level:
Hard
.