For the reaction below: H2=CHCH2-H + OH -----> H2C=CHCH2 + H-OH a. Estimate the

Question

For the reaction below:

H2=CHCH2-H + OH -----> H2C=CHCH2 + H-OH

a. Estimate the gas phase enthalpy change using bond dissociation enthalpies from the OWL Table Reference, not data from your text. Click the References button and then click the Tables link on the drop-down that appears. Include algebraic sign and units.

b. Is the reaction exothermic or endothermic?

c. Is the reaction likely to proceed spontaneously in the direction written?

For the reaction below:

CH3CH2-H + OH ------> CH3CH2 + H-OH

a. Estimate the gas phase enthalpy change using bond dissociation enthalpies from the OWL Table Reference, not data from your text. Click the References button and then click the Tables link on the drop-down that appears. Include algebraic sign and units.

b. Is the reaction exothermic or endothermic?

c. Is the reaction likely to proceed spontaneously in the direction written?

Helpful Tables:

Bond Dissociation Energies, Do298, for X-Y
kJ/mol (kcal/mol)

Additional Bond Dissociation Energies
kJ/mol (kcal/mol)

Bond Dissociation Energies, Do298, for X-Y
kJ/mol (kcal/mol)

X Y= H F Cl Br I OH NH2 CH3 CH3CH2- CN CH3- 439 (105) 452 (108) 356 (85) 293 (70) 238 (57) 385 (92) 356 (85) 377 (90) 368 (88) 510 (122) CH3CH2- 423 (101) 444 (106) 335 (80) 285 (68) 228 (53) 380 (91) 356 (85) 368 (88) 336 (80) (CH3)2CH- 409 (98) 448 (107) 339 (81) 274 (65) 226 (54) 385 (92) 351(84) (CH3)3C- 404 (97) 331 (79) 263 (63) 213 (51) 380 (91) 339 (81) CH2=CHCH2- 362 (86.5) 289 (69) 230 (55) 172 (41) 305 (73) 376 (90) 301 (72) 243 (58) 201 (48) 332 (79) CH2=CH- 465 (111) 368 (87) 259 (62) 406 (97) 536 (128) 473 (113) 527 (126) 402 (96) 337 (80.5) 274 (65) 464 (111) 427 (102) 377 (90) CH3O- 436 (104) 333 (80) H- 435 (104) 569 (136) 431 (103) 368 (88) 297 (71) 498 (119) 449 (107) 439 (105) 423 (101) 543 (130)

Explanation / Answer

1. H2C=CH-CH2-H + OH -----> H2C=CHCH2 + H-OH

Hrxn = energy required to break bonds + energy evolved when bonds are made

In the above reaction C-H bond is breaking and O-H bond is forming

Hrxn = HC-H - HO-H (CH2=CHCH2- 362 KJ/mol, HO-H = 498 KJ/mol)

Hrxn = +362 - 498 = -136 KJ/mol

Since Hrxn is -ve, it is an exothermic reaction and the reaction is spontaneous in the direction written because the energy of the system decreases.

2) CH3CH2-H + OH ------> CH3CH2 + H-OH

Hrxn = energy required to break bonds + energy evolved when bonds are made

In the above reaction C-H bond is breaking and O-H bond is forming

Hrxn = HC-H - HO-H (CH3CH2- 423 KJ/mol, HO-H = 498 KJ/mol)

Hrxn = +423 - 498 = -75 KJ/mol

Since Hrxn is -ve, it is an exothermic reaction and the reaction is spontaneous in the direction written because the energy of the system decreases.

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