For the reaction below: a. Estimate the gas phase enthalpy change using bond dis

Question

For the reaction below:

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? _________exoendoneither

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

Reference table: http://cxp.cengage.com/contentservice/assets/owms01h/references/chemtables/orgChemIndex.html

Explanation / Answer

consider the given reaction

H2C=CH2 + O=O --> 2 H2C=O

we know that

dH rxn = Bond dissociation energy of reactants - bond dissociation energy of products

so

we get

dH rxn = ( BE of O=O) + ( BE of C=C) + ( 4 x BE of C-H) - ( 2 x BE of C=O) - ( 4 x BE of C-H)

dH rxn = ( BE of O=O) + ( BE of C=C) - ( 2 x BE of C=O)

using the reference table

we get

dH rxn = ( 498) + ( 602) - ( 2 x 732)

dH rxn = -364 kJ /mol

b)

we know that

for a reaction

dH = +ve , endothermic

dH = -ve , exothermic

in this case

dH = -364 < 0 , so the reaction is exothermic

c)

yes the reaction is spontaneous in the direction written

because

the reactants have more energy than the products

so the tend to react spontaneously to form the products which have lower energy

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