Explanation 1) Concept: Fuel value is the amount of heat given off when one gram of fuel is burned. Fuel value depends on the oxygen content of the compound. The more oxygen a fuel contains, the lower is its fuel value. From the given structural formulas for the two compounds, it can be noted that formic acid has a higher content of oxygen than formaldehyde, so fuel value for formaldehyde should be higher than that of formic acid. The enthalpy of formation for formaldehyde and formic acid is given. We will write the combustion reactions of formaldehyde and formic acid, and using the ∆ H f 0 values for reactants and products, we calculate the ∆ H ° c o m b values for both. Fuel value for compounds is measured in k J / g . So, we would convert the energies from k J / m o l to k J / g using molar masses for formaldehyde and formic acid to get the fuel values for both. 2) Given: i) Standard enthalpy of formation value for formaldehyde ∆ H ° f = - 108.6 k J / m o l ii) Standard enthalpy of formation value for formic acid ∆ H ° f = - 425.0 k J / m o l iii) Mass of one mole of formic acid = 30.03 g iv) Mass of one mole of formaldehyde = 46.03 g 3) Calculations: Combustion reaction of formaldehyde can be written as: H 2 C O g + O 2 g → C O 2 g + H 2 O l ∆ H ° c o m b = ∑ n p r o d u c t s ∆ H f , p r o d u c t s 0 - ∑ n r e a c t a n t s ∆ H f , r e a c t a n t s 0 From Appendix 4, the ∆ H 0 values for C O 2 g and H 2 O l are - 393.5 k J / m o l and - 285.8 k J / m o l respectively. Using these values and the above equation, let’s calculate the ∆ H c o m b 0 value for formaldehyde as: ∆ H ° c o m b = 1 m o l × - 285.8 k J m o l + 1 m o l × - 393.5 k J m o l - 1 m o l × - 108.6 k J m o l + 1 m o l × 0 k J m o l ∆ H ° c o m b = - 679.3 k J - - 108.6 = - 679.3 + 108.6 = - 570.7 k J Calculating fuel value for formaldehyde as: 570

14th Edition

ISBN: 9780393912340

Author: Thomas R. Gilbert, Rein V. Kirss, Natalie Foster

Publisher: W. W. Norton & Company

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Chapter 19, Problem 19.111QA

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The fuel values of formaldehyde gas and liquid formic acid and determine which has the higher fuel value.

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Chapter 19, Problem 19.110QA

Chapter 19, Problem 19.112QA

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The fuel values of formaldehyde gas and liquid formic acid and determine which has the higher fuel value.

To calculate: The fuel values of formaldehyde gas and liquid formic acid and determine which has the higher fuel value.

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Chapter 19 Solutions

To calculate:

The fuel values of formaldehyde gas and liquid formic acid and determine which has the higher fuel value.