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Chapter 4: Q 41P (page 234)

Use bond-dissociation enthalpies (Table 4-2, p.203) to calculate values ofΔHfor the following reactions.

(a)

(b)

(c)

(d)

(e)

Short Answer

Expert verified

(a) ΔH = -36kJ/mol

(b) ΔH = -17kJ/mol

(c) ΔH = -19kJ/mol

(d) ΔH= -54kJ/mol

(e) ΔH = -41kJ/mol

Step by step solution

01

Bond dissociation enthalpy (BDE)

It may be defined as the amount of enthalpy required to break a bond homolytically in such a way that each bonded atom retains one of the bond’s two electrons.

Mathematically, ΔHo = ∑ (BDE of bonds broken) - ∑ (BDE of bonds formed)

02

Calculation of  ΔH

(a)

Hence, ΔH value for the reaction is ΔH = -36kJ/mol.

(b)

Hence, ΔH value for the reaction is ΔH = -17kJ/mol.

(c)

Hence, ΔH value for the reaction is ΔH = -19kJ/mol.

(d)

Hence, ΔHvalue for the reaction is ΔH= -54kJ/mol.

(e)

Hence, ΔH value for the reaction is ΔH = -41kJ/mol.

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Most popular questions from this chapter

Peroxides are often added to free-radical reactions as initiators because the oxygen-oxygen bond cleaves homolytically rather easily. For example, the bond-dissociation enthalpy of O-Obond in hydrogen peroxide (H-O-O-H)is only 213 kJ/mol (51 kcal/mol). Give a mechanism for the hydrogen peroxide- initiated reaction of cyclopentane with chlorine. The BDE for HO-Clis 210 kJ/mol (50kcal/mol).

Question: When ethene is mixed with hydrogen in the presence of a platinum catalyst, hydrogen adds across the double bond to form ethane. At room temperature, the reaction goes to completion. Predict the signs ∆H0and∆S0for this reaction. Explain these signs in terms of bonding and freedom of motion.

(a) Draw a reaction-energy diagram for the following reaction:

The activation energy is 4 kJ/mol (1 kcal/mol), and the overall for the reaction is -110 kJ/mol (-27 kcal/mol).

(b) Give the equation for the reverse reaction.

(c) What is the activation energy for the reverse reaction?

Question: The bromination of methane proceeds through the following steps:

(a) Draw a complete reaction-energy diagram for this reaction.

(b) Label the rate-limiting step.

(c) Draw the structure of each transition state

(d) Compute the overall value of∆H0for the bromination.

The following reaction has a value ofΔG0= -2.1 kJ/mol  (-0.50  kcal/mol)

CH3Br  +  H2S  ⇄  CH3SH  +  HBr

(a) Calculate Keqat room temperature(250C) for this reaction as written.

(b)Starting with a1M solution of CH3Brand H2S, calculate the final concentrations of all four species at equilibrium.

See all solutions

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