Chemistry: The Molecular Nature of Matter and Change
Chemistry: The Molecular Nature of Matter and Change
8th Edition
ISBN: 9781259631757
Author: Martin Silberberg Dr., Patricia Amateis Professor
Publisher: McGraw-Hill Education
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Chapter 6, Problem 6.90P

(a)

Interpretation Introduction

Interpretation:

ΔHrxn° for the fermentation and of respiration of sugar (C6H12O6) is to be calculated.

Concept introduction:

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 6.90P

ΔHrxn° for the fermentation and of respiration of sugar (C6H12O6) is 69.0kJ and 2538.7kJ respectively.

Explanation of Solution

The balanced chemical equation for the respiration of sugar (C6H12O6) is as follows:

C6H12O6(s)+6O2(g)6CO2(g)+6H2O(g)

The standard state of oxygen is O2(g) so the standard enthalpy of formation for O2 is zero.

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

ΔHrxn°=[{6ΔHf°[CO2(g)]+6ΔHf°[H2O(g)]}{1ΔHf°[C6H12O6(s)]+6ΔHf°[O2(g)]}] (1)

Substitute 393.5kJ/mol for ΔHf°[CO2(g)], 241.8kJ/mol for ΔHf°[H2O(g)], 1273.3kJ/mol for ΔHf°[C6H12O6(s)] and 0 for ΔHf°[O2(g)] in the equation (1).

ΔHrxn°=[{(6mol)(393.5kJ/mol)+(6mol)(241.8kJ/mol)}{(1mol)(1273.3kJ/mol)+(6mol)(0)}]=2538.656kJ2538.7kJ

The balanced chemical equation for the fermentation of sugar (C6H12O6) is as follows:

C6H12O6(s)2CO2(g)+2CH3CH2OH(l)

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

ΔHrxn°=[{2ΔHf°[CO2(g)]+2ΔHf°[CH3CH2OH(l)]}{1ΔHf°[C6H12O6(s)]}] (2)

Substitute 393.5kJ/mol for ΔHf°[CO2(g)], 277.63kJ/mol for ΔHf°[CH3CH2OH(l)] and 1273.3kJ/mol for ΔHf°[C6H12O6(s)] in the equation (2).

ΔHrxn°=[{(2mol)(393.5kJ/mol)+(2mol)(277.63kJ/mol)}{(1mol)(1273.3kJ/mol)}]=68.96kJ69.0kJ

Conclusion

ΔHrxn° for the fermentation and of respiration of sugar (C6H12O6) is 69.0kJ and 2538.7kJ respectively.

(b)

Interpretation Introduction

Interpretation:

The combustion reaction for ethanol is to be written. Whether sugar or ethanol has higher value heat of combustion per mole of C is to be determined.

Concept introduction:

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.

(b)

Expert Solution
Check Mark

Answer to Problem 6.90P

The balanced chemical equation for the respiration of enthanol (CH3CH2OH) is as follows:

CH3CH2OH(l)+3O2(g)2CO2(g)+3H2O(g)

Enthanol has higher value than sugar for heat of combustion per mole of C.

Explanation of Solution

The balanced chemical equation for the respiration of enthanol (CH3CH2OH) is as follows:

CH3CH2OH(l)+3O2(g)2CO2(g)+3H2O(g)

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

ΔHrxn°=[{2ΔHf°[CO2(g)]+3ΔHf°[H2O(g)]}{1ΔHf°[CH3CH2OH(l)]+3ΔHf°[O2(g)]}] (3)

Substitute 393.5kJ/mol for ΔHf°[CO2(g)], 241.8kJ/mol for ΔHf°[H2O(g)], 277.63kJ/mol for ΔHf°[CH3CH2OH(l)] and 0 for ΔHf°[O2(g)] in the equation (3).

ΔHrxn°=[{(2mol)(393.5kJ/mol)+(3mol)(241.8kJ/mol)}{(1mol)(277.63kJ/mol)+(3mol)(0)}]=1234.848kJ1234.8kJ

The formula to calculate the heat of combustion per mole of C in sugar is,

Heat of combustion/C=(heat of combustionmole of carbon atom in sugar) (4)

Sustitute 2538.7kJ for heat of combustion and 6mol for mole of carbon atom in sugar in equation (4).

Heat of combustion/molC=(2538.7kJ6molC)=423.1093kJ/molC423.11kJ/molC

The formula to calculate the heat of combustion per mole of C in ethanol is,

Heat of combustion/C=(heat of combustionmole of carbon atom in ethanol) (5)

Sustitute 1234.8kJ for heat of combustion and 2mol for mole of carbon atom in ethanol in equation (5).

Heat of combustion/molC=(1234.8kJ2molC)=617.424kJ/molC617.42kJ/molC

Hence, enthanol has higher value.

Conclusion

The balanced chemical equation for the respiration of enthanol (CH3CH2OH) is as follows:

CH3CH2OH(l)+3O2(g)2CO2(g)+3H2O(g)

Enthanol has higher value than sugar for heat of combustion per mole of C.

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Chapter 6 Solutions

Chemistry: The Molecular Nature of Matter and Change

Ch. 6.3 - When 25.0 mL of 2.00 M HNO3 and 50.0 mL of 1.00 M...Ch. 6.3 - Prob. 6.6BFPCh. 6.3 - Prob. 6.7AFPCh. 6.3 - Prob. 6.7BFPCh. 6.4 - Prob. 6.8AFPCh. 6.4 - Prob. 6.8BFPCh. 6.5 - Prob. 6.9AFPCh. 6.5 - Prob. 6.9BFPCh. 6.6 - Prob. 6.10AFPCh. 6.6 - Prob. 6.10BFPCh. 6.6 - Prob. 6.11AFPCh. 6.6 - Prob. 6.11BFPCh. 6.6 - Prob. B6.1PCh. 6.6 - Prob. B6.2PCh. 6 - Prob. 6.1PCh. 6 - Prob. 6.2PCh. 6 - Prob. 6.3PCh. 6 - Prob. 6.4PCh. 6 - Prob. 6.5PCh. 6 - Prob. 6.6PCh. 6 - Prob. 6.7PCh. 6 - Prob. 6.8PCh. 6 - Prob. 6.9PCh. 6 - A system releases 255 cal of heat to the...Ch. 6 - What is the change in internal energy (in J) of a...Ch. 6 - Prob. 6.12PCh. 6 - Prob. 6.13PCh. 6 - Thermal decomposition of 5.0 metric tons of...Ch. 6 - Prob. 6.15PCh. 6 - The external pressure on a gas sample is 2660...Ch. 6 - The nutritional calorie (Calorie) is equivalent to...Ch. 6 - If an athlete expends 1950 kJ/h, how long does it...Ch. 6 - Prob. 6.19PCh. 6 - Hot packs used by skiers produce heat via the...Ch. 6 - Prob. 6.21PCh. 6 - Prob. 6.22PCh. 6 - For each process, state whether ΔH is less than...Ch. 6 - Prob. 6.24PCh. 6 - Prob. 6.25PCh. 6 - Prob. 6.26PCh. 6 - Prob. 6.27PCh. 6 - Prob. 6.28PCh. 6 - Prob. 6.29PCh. 6 - Prob. 6.30PCh. 6 - Prob. 6.31PCh. 6 - Prob. 6.32PCh. 6 - What data do you need to determine the specific...Ch. 6 - Is the specific heat capacity of a substance an...Ch. 6 - Prob. 6.35PCh. 6 - Both a coffee-cup calorimeter and a bomb...Ch. 6 - Find q when 22.0 g of water is heated from 25.0°C...Ch. 6 - Calculate q when 0.10 g of ice is cooled from...Ch. 6 - A 295-g aluminum engine part at an initial...Ch. 6 - Prob. 6.40PCh. 6 - Two iron bolts of equal mass—one at 100.°C, the...Ch. 6 - Prob. 6.42PCh. 6 - Prob. 6.43PCh. 6 - Prob. 6.44PCh. 6 - Prob. 6.45PCh. 6 - A 30.5-g sample of an alloy at 93.0°C is placed...Ch. 6 - When 25.0 mL of 0.500 M H2SO4 is added to 25.0 mL...Ch. 6 - Prob. 6.48PCh. 6 - Prob. 6.49PCh. 6 - A chemist places 1.750 g of ethanol, C2H6O, in a...Ch. 6 - High-purity benzoic acid (C6H5COOH; ΔH for...Ch. 6 - Two aircraft rivets, one iron and the other...Ch. 6 - A chemical engineer burned 1.520 g of a...Ch. 6 - Prob. 6.54PCh. 6 - Prob. 6.55PCh. 6 - Prob. 6.56PCh. 6 - Consider the following balanced thermochemical...Ch. 6 - Prob. 6.58PCh. 6 - Prob. 6.59PCh. 6 - When 1 mol of KBr(s) decomposes to its elements,...Ch. 6 - Prob. 6.61PCh. 6 - Compounds of boron and hydrogen are remarkable for...Ch. 6 - Prob. 6.63PCh. 6 - Prob. 6.64PCh. 6 - Prob. 6.65PCh. 6 - Prob. 6.66PCh. 6 - Prob. 6.67PCh. 6 - Prob. 6.68PCh. 6 - Prob. 6.69PCh. 6 - Prob. 6.70PCh. 6 - Prob. 6.71PCh. 6 - Write the balanced overall equation (equation 3)...Ch. 6 - Prob. 6.73PCh. 6 - Prob. 6.74PCh. 6 - Prob. 6.75PCh. 6 - Prob. 6.76PCh. 6 - Prob. 6.77PCh. 6 - Prob. 6.78PCh. 6 - Prob. 6.79PCh. 6 - Prob. 6.80PCh. 6 - Prob. 6.81PCh. 6 - Prob. 6.82PCh. 6 - Calculatefor each of the following: SiO2(s) +...Ch. 6 - Prob. 6.84PCh. 6 - Prob. 6.85PCh. 6 - The common lead-acid car battery produces a large...Ch. 6 - Prob. 6.87PCh. 6 - Prob. 6.88PCh. 6 - Prob. 6.89PCh. 6 - Prob. 6.90PCh. 6 - Prob. 6.91PCh. 6 - Prob. 6.92PCh. 6 - The following scenes represent a gaseous reaction...Ch. 6 - Prob. 6.94PCh. 6 - Prob. 6.95PCh. 6 - Prob. 6.96PCh. 6 - Prob. 6.97PCh. 6 - Prob. 6.98PCh. 6 - Prob. 6.99PCh. 6 - Prob. 6.100PCh. 6 - Prob. 6.101PCh. 6 - Prob. 6.102PCh. 6 - Prob. 6.103PCh. 6 - Prob. 6.104PCh. 6 - Prob. 6.105PCh. 6 - Prob. 6.106PCh. 6 - Liquid methanol (CH3OH) canbe used as an...Ch. 6 - Prob. 6.108P
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