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Ch.5 - Thermochemistry
All textbooksBrown 14th EditionCh.5 - ThermochemistryProblem 89
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Chapter 5, Problem 89

(a) What is meant by the term fuel value? (b) Which is a greater source of energy as food, 5 g of fat or 9 g of carbohydrate?

Verified step by step guidance
1
Step 1: Understand the term 'fuel value'. In chemistry, the fuel value refers to the amount of energy released when a substance is completely combusted. It is usually expressed in units of energy per mass, such as kilojoules per gram (kJ/g) or calories per gram (cal/g).
Step 2: Identify the typical fuel values for fats and carbohydrates. Fats generally have a higher fuel value, approximately 9 kcal/g, while carbohydrates have a fuel value of about 4 kcal/g.
Step 3: Calculate the total energy provided by 5 g of fat. Multiply the mass of the fat by its fuel value: 5 g * 9 kcal/g.
Step 4: Calculate the total energy provided by 9 g of carbohydrate. Multiply the mass of the carbohydrate by its fuel value: 9 g * 4 kcal/g.
Step 5: Compare the total energy values obtained from the calculations in Steps 3 and 4 to determine which provides a greater source of energy.
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Related Practice
Textbook Question

(a) The nitrogen atoms in an N2 molecule are held together by a triple bond; use enthalpies of formation in Appendix C to estimate the enthalpy of this bond, D(N‚N). (b) Consider the reaction between hydrazine and hydrogen to produce ammonia, N2H41g2 + H21g2¡2 NH31g2. Use enthalpies of formation and bond enthalpies to estimate the enthalpy of the nitrogen– nitrogen bond in N2H4. (c) Based on your answers to parts (a) and (b), would you predict that the nitrogen–nitrogen bond in hydrazine is weaker than, similar to, or stronger than the bond in N2 ?

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Textbook Question

Consider the reaction 2 H2(g) + O2(g) → 2 H2O(l). (a) Use the bond enthalpies in Table 5.4 to estimate H for this reaction, ignoring the fact that water is in the liquid state.

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Open Question
Consider the reaction H2(g) + Br2(l) → 2 HBr(g). (b) Without doing a calculation, predict whether your estimate in part (a) is more negative or less negative than the true reaction enthalpy.
Textbook Question

(b) A particular chip snack food is composed of 12% protein, 14% fat, and the rest carbohydrate. What percentage of the calorie content of this food is fat?

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Textbook Question

(a) A serving of a particular ready-to-serve brown & wild rice meal contains 4.5 g fat, 42 g carbohydrate, and 4.0 g protein. Estimate the number of calories in a serving.

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Open Question
A hamburger contains 28 g fat, 46 g carbohydrate, and 25 g protein. What is the fuel value in kJ in one hamburger? How many calories does it provide?