Loose Leaf for Chemistry: The Molecular Nature of Matter and Change
Loose Leaf for Chemistry: The Molecular Nature of Matter and Change
8th Edition
ISBN: 9781260151749
Author: Silberberg Dr., Martin; Amateis Professor, Patricia
Publisher: McGraw-Hill Education
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Chapter 9, Problem 9.91P

(a)

Interpretation Introduction

Interpretation:

ΔHrxn° for gas-phase hydration of ethylene to ethanol by the use of bond energies and enthalpies of formation is to be determined.

Concept introduction:

The heat of the reaction (ΔHrxn°) is defined as the heat released or absorbed during a chemical reaction as a result of the difference in the bond energies (BE) of reactant and product in the reaction. ΔHrxn° is negative for exothermic reaction and ΔHrxn° is positive for an endothermic reaction.

The formula to calculate ΔHrxn° of reaction is as follows:

ΔHrxn°=ΔHreactant bond broken°+ΔHproduct bond formed°

Or,

ΔHrxn°=BEreactant bond brokenBEproduct bond formed

The bond energy of reactants is positive and the bond energy of products is negative.

The standard enthalpy of reaction is calculated by the summation of standard enthalpy of formation of the product minus the summation of standard enthalpy of formation of product at the standard conditions. The formula to calculate the standard enthalpy of reaction (ΔHrxn°) is as follows:

ΔHrxn°=mΔHf (products)°mΔHf (reactants)°

Here, m and n are the stoichiometric coefficients of reactants and product in the balanced chemical equation.

(a)

Expert Solution
Check Mark

Answer to Problem 9.91P

ΔHrxn° for gas-phase hydration of ethylene to ethanol by the use of bond energies and enthalpies of formation is 37kJ and 45.7kJ respectively.

Explanation of Solution

The given chemical equation for the gas-phase hydration of ethylene to ethanol is as follows:

Loose Leaf for Chemistry: The Molecular Nature of Matter and Change, Chapter 9, Problem 9.91P

The number of broken bonds is 4 CH bond, 1 C=C bond, and 2 OH bonds.

The number of bonds formed is 5 CH bonds, 1 CO, 1 CC and 1 OH bonds.

The formula to the enthalpy of the given reaction is as follows:

ΔHrxn°=(4BECH+1BEC=C+2BEOH)(5BECH+1BECO+1BECC+1BEOH) (1)

Substitute 413kJ/mol for BECH, 614kJ/mol for BEC=C, 358kJ/mol for BECO, 347kJ/mol for BECC and 467kJ/mol for BEOH in the equation (1).

ΔHrxn°=[((4 mol)(413kJ/mol)+(1 mol)(617kJ/mol)+(2 mol)(467kJ/mol))(5 mol)(413kJ/mol)+(1 mol)(358kJ/mol)+(1 mol)(347kJ/mol)+(1 mol)(467kJ/mol)]=37kJ

The formula to calculate the standard enthalpy of reaction (ΔHrxn°) is as follows:

ΔHrxn°=[{ΔHf°[CH3CH2OH(g)]}{ΔHf°[CH2=CH2(g)]+ΔHf°[H2O(g)]}] (2)

Substitute 235.1kJ/mol for ΔHf°[CH3CH2OH(g)], 52.47kJ/mol for ΔHf°[CH2=CH2(g)] and 241.826kJ for ΔHf°[H2O(g)] in the equation (2).

ΔHrxn°=[{(1mol)(235.1kJ/mol)}{(1mol)(52.47kJ/mol)+(1mol)(241.826kJ)}]=45.744kJ45.7kJ

Conclusion

ΔHrxn° for gas-phase hydration of ethylene to ethanol by the use of bond energies and enthalpies of formation is 37kJ and 45.7kJ respectively.

(b)

Interpretation Introduction

Interpretation:

ΔHrxn° for the hydrolysis of ethylene glycol is to be calculated.

Concept introduction:

The heat of the reaction (ΔHrxn°) is defined as the heat released or absorbed during a chemical reaction as a result of the difference in the bond energies (BE) of reactant and product in the reaction. ΔHrxn° is negative for exothermic reaction and ΔHrxn° is positive for an endothermic reaction.

The formula to calculate ΔHrxn° of reaction is as follows:

ΔHrxn°=ΔHreactant bond broken°+ΔHproduct bond formed°

Or,

ΔHrxn°=BEreactant bond brokenBEproduct bond formed

The bond energy of reactants is positive and the bond energy of products is negative.

(b)

Expert Solution
Check Mark

Answer to Problem 9.91P

ΔHrxn° for the hydrolysis of ethylene glycol is 0.

Explanation of Solution

The given chemical equation for the hydrolysis of ethylene glycol is as follows:

C2H4O(l)+H2O(l)C2H6O2(l)

The number of broken bonds is 4 CH bond, 1 CC bond, 2 CO bond, and 2 OH bonds.

The number of bonds formed is 4 CH bond, 1 CC bond, 2 CO bond, and 2 OH bonds.

The formula to the enthalpy of the given reaction is as follows:

ΔHrxn°=[(4BECH+1BECC+1BECO+2BEOH)(4BECH+1BECC+1BECO+2BEOH)] (3)

Substitute 413kJ/mol for BECH, 358kJ/mol for BECO, 347kJ/mol for BECC and 467kJ/mol for BEOH in the equation (3).

ΔHrxn°=[((4 mol)(413kJ/mol)+(2 mol)(358kJ/mol)+(1 mol)(347kJ/mol)+(2 mol)(467kJ/mol))((4 mol)(413kJ/mol)+(2 mol)(358kJ/mol)+(1 mol)(347kJ/mol)+(2 mol)(467kJ/mol))]=0

Conclusion

ΔHrxn° for the hydrolysis of ethylene glycol is 0.

(c)

Interpretation Introduction

Interpretation:

The reason for the relatively closer value for the hydration in part (a) but not that close for the hydrolysis in part (b) is to be determined.

Concept introduction:

Bond energy is the amount of energy needed to break a bond between two gaseous atoms. Bond energy is measured in kJ/mol. The heat of the reaction (ΔHrxn°) is defined as the heat released or absorbed during a chemical reaction as a result of the difference in the bond energies (BE) of reactant and product in the reaction. ΔHrxn° is negative for exothermic reaction and ΔHrxn° is positive for an endothermic reaction.

The formula to calculate ΔHrxn° of reaction is as follows:

ΔHrxn°=ΔHreactant bond broken°+ΔHproduct bond formed°

Or,

ΔHrxn°=BEreactant bond brokenBEproduct bond formed

The bond energy of reactants is positive and the bond energy of products is negative.

(c)

Expert Solution
Check Mark

Answer to Problem 9.91P

In part (b), the same number of similar bonds are broken in the reactant side and formed in the product side so the value of the enthalpy change is zero. Bond energy is generally specific for a bond and remains the same in different molecules.

Explanation of Solution

Bond energy is generally specific for a bond and depends upon the strength of the bond. The bond energy value is the average value so remain same in different molecules.

In part (b), the same number of similar bonds are broken in the reactant side and formed in the product side so the value of the enthalpy change is zero.

For example, the value of bond energy of OH is similar in water and ethyl glycol. Therefore, the bond energy depends upon the strength of the bond but not the molecule.

Conclusion

The bond energy value is the average value so the bond energy of the same bond in different molecules remains same.

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Chapter 9 Solutions

Loose Leaf for Chemistry: The Molecular Nature of Matter and Change

Ch. 9.5 - Prob. 9.5AFPCh. 9.5 - Prob. 9.5BFPCh. 9 - Prob. 9.1PCh. 9 - Prob. 9.2PCh. 9 - What is the relationship between the tendency of a...Ch. 9 - Prob. 9.4PCh. 9 - Prob. 9.5PCh. 9 - State the type of bonding—ionic, covalent, or...Ch. 9 - State the type of bonding—ionic, covalent, or...Ch. 9 - State the type of bonding—ionic, covalent, or...Ch. 9 - Prob. 9.9PCh. 9 - Prob. 9.10PCh. 9 - Prob. 9.11PCh. 9 - Prob. 9.12PCh. 9 - Prob. 9.13PCh. 9 - Give the group number and condensed electron...Ch. 9 - Give the group number and condensed electron...Ch. 9 - Prob. 9.16PCh. 9 - Prob. 9.17PCh. 9 - Prob. 9.18PCh. 9 - Prob. 9.19PCh. 9 - Prob. 9.20PCh. 9 - Prob. 9.21PCh. 9 - Prob. 9.22PCh. 9 - Prob. 9.23PCh. 9 - Prob. 9.24PCh. 9 - Prob. 9.25PCh. 9 - For each pair, choose the compound with the larger...Ch. 9 - Prob. 9.27PCh. 9 - For each pair, choose the compound with the...Ch. 9 - Prob. 9.29PCh. 9 - Use the following to calculate of NaCl: Compared...Ch. 9 - Use the following to calculate of MgF2: Compared...Ch. 9 - Prob. 9.32PCh. 9 - Born-Haber cycles were used to obtain the first...Ch. 9 - Prob. 9.34PCh. 9 - Prob. 9.35PCh. 9 - Prob. 9.36PCh. 9 - How does the energy of the bond between a given...Ch. 9 - When liquid benzene (C6H6) boils, does the gas...Ch. 9 - Prob. 9.39PCh. 9 - Prob. 9.40PCh. 9 - Prob. 9.41PCh. 9 - Prob. 9.42PCh. 9 - The text points out that, for similar types of...Ch. 9 - Why is there a discrepancy between an enthalpy of...Ch. 9 - Which of the following gases would you expect to...Ch. 9 - Which of the following gases would you expect to...Ch. 9 - Use bond energies to calculate the enthalpy of...Ch. 9 - Prob. 9.48PCh. 9 - Prob. 9.49PCh. 9 - Prob. 9.50PCh. 9 - Prob. 9.51PCh. 9 - What is the general relationship between IE1 and...Ch. 9 - Is the H—O bond in water nonpolar covalent, polar...Ch. 9 - Prob. 9.54PCh. 9 - How is the partial ionic character of a bond in a...Ch. 9 - Using the periodic table only, arrange the...Ch. 9 - Prob. 9.57PCh. 9 - Prob. 9.58PCh. 9 - Prob. 9.59PCh. 9 - Prob. 9.60PCh. 9 - Use Figure 9.21 to indicate the polarity of each...Ch. 9 - Prob. 9.62PCh. 9 - Prob. 9.63PCh. 9 - Prob. 9.64PCh. 9 - Prob. 9.65PCh. 9 - Prob. 9.66PCh. 9 - Prob. 9.67PCh. 9 - Prob. 9.68PCh. 9 - Prob. 9.69PCh. 9 - Prob. 9.70PCh. 9 - Prob. 9.71PCh. 9 - Geologists have a rule of thumb: when molten rock...Ch. 9 - Prob. 9.73PCh. 9 - Use Lewis electron-dot symbols to represent the...Ch. 9 - Prob. 9.75PCh. 9 - Prob. 9.76PCh. 9 - By using photons of specific wavelengths, chemists...Ch. 9 - Prob. 9.78PCh. 9 - Prob. 9.79PCh. 9 - Prob. 9.80PCh. 9 - Prob. 9.81PCh. 9 - Prob. 9.82PCh. 9 - Prob. 9.83PCh. 9 - Find the longest wavelengths of light that can...Ch. 9 - The work function (ϕ) of a metal is the minimum...Ch. 9 - Prob. 9.86PCh. 9 - Prob. 9.87PCh. 9 - Prob. 9.88PCh. 9 - In a future hydrogen-fuel economy, the cheapest...Ch. 9 - Prob. 9.90PCh. 9 - Prob. 9.91P
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