Enthalpy of Formation

Textbook Question

What is ΔH for the explosion of nitroglycerin? (LO 9.14) 2 C3H5(NO3)3(l) → 3 N2(g) + 1/2 O2(g) + 6 CO2(g) + 5 H2O(g) (a) −315.0 kJ (b) −4517 kJ (c) −3425 kJ (d) −3062 kJ

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Textbook Question

Atomic hydrogen (H) is used in welding (AHW). The atoms recombine to hydrogen molecules with a large release of heat according to the following reaction: 2 H1g2 ¡H21g2 (b) Which has the higher enthalpy under these conditions, 2 H1g2 or H21g2?

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Textbook Question

Consider the following equilibrium between oxides of nitrogen 3 NO1g2 Δ NO21g2 + N2O1g2 (a) Use data in Appendix C to calculate H for this reaction.

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Textbook Question

Methanol 1CH3OH2 can be made by the reaction of CO with H2: CO1g2 + 2 H21g2 Δ CH3OH1g2 (a) Use thermochemical data in Appendix C to calculate H for this reaction.

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Textbook Question

Acetylene 1C2H21g22 is used for welding because oxyacetylene is the hottest burning common fuel gas. Using standard enthalpies of formation, calculate the quantity of heat produced when 10 g of acetylene is completely combusted in air under standard conditions.

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Textbook Question

The fuel in high-efficiency natural-gas vehicles consists primarily of methane 1CH42. (a) How much heat is produced in burning 1 mol of CH41g2 under standard conditions if reactants and products are brought to 298 K and H2O1l2 is formed?

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Textbook Question

Using values from Appendix C, calculate the value of H for each of the following reactions: (a) CaO1s2 + 2HF1g2¡ CaF21s2 + H2O1g2

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Textbook Question

Zinc metal reacts with hydrochloric acid according to the balanced equation: Zn(s) + 2 HCl(aq)¡ZnCl2(aq) + H2( g) When 0.103 g of Zn(s) is combined with enough HCl to make 50.0 mL of solution in a coffee-cup calorimeter, all of the zinc reacts, raising the temperature of the solution from 22.5 °C to 23.7 °C. Find ΔHrxn for this reaction as written. (Use 1.0 g>mL for the density of the solution and 4.18 J>g # °C as the specific heat capacity.)

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Textbook Question

Complete combustion of 1 mol of acetone 1C3H6O2 liberates 1790 kJ: C3H6O1l2 + 4 O21g2 ¡ 3 CO21g2 + 3 H2O1l2 H° = -1790 kJ Using this information together with the standard enthalpies of formation of O21g2, CO21g2, and H2O1l2 from Appendix C, calculate the standard enthalpy of formation of acetone.

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Textbook Question

Calcium carbide 1CaC22 reacts with water to form acetylene 1C2H22 and Ca1OH22. From the following enthalpy of reaction data and data in Appendix C, calculate Hf° for CaC21s2: CaC21s2 + 2 H2O1l2 ¡ Ca1OH221s2 + C2H21g2 H° = -127.2 kJ

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Textbook Question

Gasoline is composed primarily of hydrocarbons, including many with eight carbon atoms, called octanes. One of the cleanest–burning octanes is a compound called 2,3,4- trimethylpentane, which has the following structural formula: The complete combustion of one mole of this compound to CO21g2 and H2O1g2 leads to H° = -5064.9 kJ. (b) By using the information in this problem and data in Table 5.3, calculate Hf° for 2,3,4-trimethylpentane.

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Textbook Question

Ethanol 1C2H5OH2 is blended with gasoline as an automobile fuel. (d) Calculate the mass of CO2 produced per kJ of heat emitted.

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Textbook Question

Ethanol 1C2H5OH2 is blended with gasoline as an automobile fuel. (c) Calculate the heat produced per liter of ethanol by combustion of ethanol under constant pressure. Ethanol has a density of 0.789 g>mL.

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Textbook Question

Methanol 1CH3OH2 is used as a fuel in race cars. (b) Calculate the standard enthalpy change for the reaction, assuming H2O1g2 as a product.

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Textbook Question

Hydrazine (N₂H₄) is a fuel used by some spacecraft. It is normally oxidized by N₂O₄ according to the equation: N₂H₄(l) + N₂O₄ (g) → 2 N₂O (g) + 2 H₂O (g) Calculate ΔH°_rxn for this reaction using standard enthalpies of formation.

Pentane (C5H12) is a component of gasoline that burns according to the following balanced equation: C5H12(l ) + 8 O2( g)¡5 CO2( g) + 6 H2O( g) Calculate ΔH °rxn for this reaction using standard enthalpies of formation. (The standard enthalpy of formation of liquid pentane is -146.8 kJ>mol.)

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Textbook Question

Use standard enthalpies of formation to calculate ΔH °rxn for each reaction. d. Cr2O3(s) + 3 CO( g)¡2 Cr(s) + 3 CO2( g)

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Textbook Question

Use standard enthalpies of formation to calculate ΔH °rxn for each reaction. c. 3 NO2( g) + H2O(l )¡2 HNO3(aq) + NO( g)

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Textbook Question

Use standard enthalpies of formation to calculate ΔH °rxn for each reaction. a. C2H4( g) + H2( g)¡C2H6( g)

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Textbook Question

Use standard enthalpies of formation to calculate ΔH °rxn for each reaction. a. 2 H2S( g) + 3 O2( g)¡2 H2O(l ) + 2 SO2( g)

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Textbook Question

Use standard enthalpies of formation to calculate ΔH °rxn for each reaction. b. SO2( g) + 12 O2( g)¡SO3( g)

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Textbook Question

Ethanol (C2H5OH) can be made from the fermentation of crops and has been used as a fuel additive to gasoline. Write a balanced equation for the combustion of ethanol and calculate ΔH °rxn.

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Textbook Question

Top fuel dragsters and funny cars burn nitromethane as fuel according to the balanced combustion equation: 2 CH3NO2(l ) + 32O2( g)¡2 CO2( g) + 3 H2O(l ) + N2( g) ΔH °rxn = -1418 kJ The enthalpy of combustion for nitromethane is -709.2 kJ>mol. Calculate the standard enthalpy of formation (ΔH °f ) for nitromethane.

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Textbook Question

The explosive nitroglycerin (C3H5N3O9) decomposes rapidly upon ignition or sudden impact according to the balanced equation: 4 C3H5N3O9(l )¡12 CO2( g) + 10 H2O( g) + 6 N2( g) + O2( g) ΔH °rxn = -5678 kJ Calculate the standard enthalpy of formation (ΔH °f ) for nitroglycerin.

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Textbook Question

Methanol (CH3OH) has been suggested as a fuel to replace gasoline. Find ΔH °rxn, and determine the mass of carbon dioxide emitted per kJ of heat produced. Use the information from the previous exercise to calculate the same quantity for octane, C8H18. How does methanol compare to octane with respect to global warming?

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Textbook Question

All the oxides of nitrogen have positive values of ΔGf° at 298 K, but only one common oxide of nitrogen has a positive ΔSf°. Identify that oxide of nitrogen without reference to thermodynamic data and explain.

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Textbook Question

The standard enthalpies of formation of gaseous propyne 1C3H42, propylene 1C3H62, and propane 1C3H82 are +185.4, +20.4, and -103.8 kJ>mol, respectively. (c) Which is the most efficient fuel in terms of heat evolved per unit mass?

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Textbook Question

The standard enthalpies of formation of gaseous propyne 1C3H42, propylene 1C3H62, and propane 1C3H82 are +185.4, +20.4, and -103.8 kJ>mol, respectively. (b) Calculate the heat evolved on combustion of 1 kg of each substance.

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Textbook Question

It is interesting to compare the 'fuel value' of a hydrocarbon in a hypothetical world where oxygen is not the combustion agent. The enthalpy of formation of CF41g2 is -679.9 kJ>mol. Which of the following two reactions is the more exothermic? CH41g2 + 2 O21g2 ¡ CO21g2 + 2 H2O1g2 CH41g2 + 4 F21g2 ¡ CF41g2 + 4 HF1g2

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Textbook Question

What is a compound's standard heat of formation?

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Textbook Question

Use standard enthalpies of formation to calculate the standard change in enthalpy for the melting of ice. (The ΔH °f for H2O(s) is -291.8 kJ/mol.)

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Textbook Question

Calculate ∆H°f in kJ/mol for benzene, C6H6, from the following data: 2 C6H6(l) + 15 O2(g) → 12 CO2(g) + 6 H2O(l) ∆H°=-6534 kJ ∆H°f (CO2) = -393.5 kJ/mol ∆H°f(H2O) = -285.8 kJ/mol

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Textbook Question

Acetylene 1C2H22 and nitrogen 1N22 both contain a triple bond, but they differ greatly in their chemical properties. (b) By referring to Appendix C, look up the enthalpies of formation of acetylene and nitrogen. Which compound is more stable?

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Textbook Question

Hydrogen and methanol have both been proposed as alternatives to hydrocarbon fuels. To compare the energy of these fuels to that of octane (C8H18), calculate the energy released per kilogram of octane.

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Textbook Question

Hydrogen and methanol have both been proposed as alternatives to hydrocarbon fuels. Which fuel contains the most energy in the least mass?

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Textbook Question

Acetic acid (CH3CO2H), whose aqueous solutions are known as vinegar, is prepared by reaction of ethyl alcohol (CH3CH2OH) with oxygen: CH3CH2OH(l) + O2(g) → CH3CO2H(l) + H2O(l) Use the following data to calculate ∆H° in kilojoules for the reaction: ∆H°f [CH3CH2OH(l)] = -277.7 kJ/mol ∆H°f [CH3CO2H(l)] = -484.5 kJ/mol ∆H°f [H2O(l)] = -285.8 kJ/mol

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Textbook Question

Styrene (C8H8), the precursor of polystyrene polymers, has a standard heat of combustion of -4395 kJ/mol. Write a balanced equation for the combustion reaction, and calculate ΔH°f for styrene in kJ/mol. ΔH°f [CO2(g)] = -393.5 kJ/mol; ΔH°f [H2O(l)] = -285.8 kJ/mol

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Textbook Question

Under certain nonstandard conditions, oxidation by O2( g) of 1 mol of SO2( g) to SO3( g) absorbs 89.5 kJ. The enthalpy of formation of SO3( g) is -204.2 kJ under these conditions. Find the enthalpy of formation of SO2( g).

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Textbook Question

Methyl tert-butyl ether (MTBE), C5H12O, a gasoline additive used to boost octane ratings, has ΔH°f = -313.6 kJ/mol. Write a balanced equaiton for its combustion reaciton, and calcualte its standard heat of combustion in kilojoules

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Textbook Question

Methyl tert-butyl ether (MTBE) is prepared by reaciton of methanol (l) (ΔH°f = -239.2 kJ/mol) with 2-methyl-propene (g), according to the requation Calculate ΔH°f in kJ/mol for 2-methylpropene

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Textbook Question

Given the standard heats of formation shown in Appendix B, what is ΔH° in kilojoules for the reaciton CaCO3(s) → CaO(s) + CO2(g)?

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Textbook Question

The ΔH for the oxidation of sulfur in the gas phase to SO3 is -204 kJ/mol and for the oxidation of SO2 to SO3 is 89.5 kJ/mol. Find the enthalpy of formation of SO2 under these conditions.

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Textbook Question

Given the standard heats of formation shown in Appendix B, what is ΔH° in kilojoules for the reaciton 3 N2O4(g) + 2 H2O(l) → 4 HNO3(aq) + 2 NO(g)

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Textbook Question

When magnesium metal is burned in air (Figure 3.6), two products are produced. One is magnesium oxide, MgO. The other is the product of the reaction of Mg with molecular nitrogen, magnesium nitride. When water is added to magnesium nitride, it reacts to form magnesium oxide and ammonia gas. (e) The standard enthalpy of formation of solid magnesium nitride is -461.08 kJ>mol. Calculate the standard enthalpy change for the reaction between magnesium metal and ammonia gas.

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Textbook Question

Calcualte ΔH° in kilojoules for the synthesis of lime (CaO) from limestone (CaCO3), the key step in the manufacture of cement. CaCO3(s) → CaO(s) + CO2(g) ΔH°f [CaCO3(s)] = -1207.6 kJ/mol ΔH°f [CaO(s)] = -634.9 kJ/mol ΔH°f [CO2(g)] = -393.5 kJ/mol

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Textbook Question

Use the information in Table 9.2 to calculate ΔH° in kilojoules for the photosynthesis of glucose (C6H12O6) and O2 from CO2 and liquid H2O, a reaciton carried out by all green plants

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Textbook Question

Use the data in Appendix B to find standard enthalpies of reaction in kilojoules for the following processes: (c) Fe2O3 (s) + 3 CO (g) → Fe(s) + 3 CO2(g)

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Textbook Question

Use the data in Appendix B to find standard enthalpies of reaction in kilojoules for the following processes: (b) 2 H2O2 (aq) → 2 H2O (l) + O2(g)

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Textbook Question

Use the data in Appendix B to find standard enthalpies of reaction in kilojoules for the following processes: (a) C(s) + CO2(g) → 2 CO(g)

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Textbook Question

Isooctane, C8H18, is the component of gasoline from which the term octane rating derives (b) The standard molar heat of combustion of isooctane (l) is -5461 kJ/mol. Calculate ΔH°f for isooctane(l)

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Textbook Question

The mechanism for the oxidation of HBr by O2 to form 2 H2O and Br2 is shown in Exercise 14.74. (a) Calculate the overall standard enthalpy change for the reaction process.

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Textbook Question

Consider the following acid-neutralization reactions involving the strong base NaOH(aq): HNO31aq2 + NaOH1aq2¡NaNO31aq2 + H2O1l2 HCl1aq2 + NaOH1aq2¡NaCl1aq2 + H2O1l2 NH4+1aq2 + NaOH1aq2¡NH31aq2 + Na+1aq2 + H2O1l2 (d) In the third equation NH4 +1aq2 is acting as an acid. Based on the value of H° for this reaction, do you think it is a strong or a weak acid? Explain.

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Textbook Question

The methane molecule, CH4, has the geometry shown in Figure 2.17. Imagine a hypothetical process in which the methane molecule is 'expanded,' by simultaneously extending all four C—H bonds to infinity. We then have the process CH41g2¡C1g2 + 4 H1g2 (a) Compare this process with the reverse of the reaction that represents the standard enthalpy of formation of CH41g2.

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Textbook Question

One of the best-selling light, or low-calorie, beers is 4.2% alcohol by volume and a 355-mL serving contains 110 Calories; remember: 1 Calorie = 1000 cal = 1 kcal. To estimate the percentage of Calories that comes from the alcohol, consider the following questions. (a) Write a balanced chemical equation for the reaction of ethanol, C2H5OH, with oxygen to make carbon dioxide and water. (b) Use enthalpies of formation in Appendix C to determine ΔH for this reaction. (c) If 4.2% of the total volume is ethanol and the density of ethanol is 0.789 g/mL, what mass of ethanol does a 355-mL serving of light beer contain? (d) How many Calories are released by the metabolism of ethanol, the reaction from part (a)? (e) What percentage of the 110 Calories comes from the ethanol?

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Textbook Question

Metallic mercury is obtained by heating the mineral cinnabar (HgS) in air: HgS1s2 + O21g2 S Hg1l2 + SO21g2 (a) Use the data in Appendix B to calculate ΔH° in kilojoules for the reaction.

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Textbook Question

Methanol 1CH3OH2 is made industrially in two steps from CO and H2. It is so cheap to make that it is being considered for use as a precursor to hydrocarbon fuels, such as methane 1CH42: Step 1. CO1g2 + 2 H21g2 S CH3OH1l2 ΔS° = - 332 J>K Step 2. CH3OH1l2 S CH41g2 + 1>2 O21g2 ΔS° = 162 J>K (f) Calculate ΔH° for step 2.

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Textbook Question

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Textbook Question

When a gaseous compound X containing only C, H, and O is burned in O2, 1 volume of the unknown gas reacts with 3 volumes of O2 to give 2 volumes of CO2 and 3 volumes of gaseous H2O. Assume all volumes are measured at the same temperature and pressure. (d) Combustion of 5.000 g of X releases 144.2 kJ heat. Look up ΔH°f values for CO21g2 and H2O1g2 in Appendix B, and calculate ΔH°f for compound X.

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Textbook Question

Combustion analysis of 0.1500 g of methyl tert-butyl ether, an octane booster used in gasoline, gave 0.3744 g of CO2 and 0.1838 g of H2O. When a flask having a volume of 1.00 L was evacuated and then filled with methyl tertbutyl ether vapor at a pressure of 100.0 kPa and a temperature of 54.8 °C, the mass of the flask increased by 3.233 g. (d) The enthalpy of combustion for methyl tert-butyl ether is ΔH° combustion = -3368.7 kJ>mol. What is its standard enthalpy of enthalpy of formation, ΔH°f?

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Textbook Question

Acid spills are often neutralized with sodium carbonate or sodium hydrogen carbonate. For neutralization of acetic acid, the unbalanced equations are 112 CH3CO2H1l2 + Na2CO31s2 S CH3CO2Na1aq2 + CO21g2 + H2O1l2 122 CH3CO2H1l2 + NaHCO31s2 CH3CO2Na1aq2 + CO21g2 + H2O1l2 (c) How much heat in kilojoules is absorbed or liberated in each reaction? See Appendix B for standard heats of for- mation; ΔH°f = - 726.1 kJ>mol for CH3CO2 Na(aq).

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Textbook Question

(b) Use the data in Appendix B to calculate ΔH° for the reaction of potassium metal with water.

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Open Question

Calculate the enthalpy of the reaction 2NO(g) + O₂(g) → 2NO₂(g) given the following reactions and enthalpies of formation: 12N₂(g) + O₂(g) → NO₂(g), δH^∘_a=33.2 kJ 12N₂(g) + 12O₂(g) → NO(g), δH^∘_b=90.2 kJ

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Open Question

What is the isobaric heat of combustion for ethane, C₂H₆(g), in kJ per mole of ethane at 298.15 k?

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Open Question

How much energy is required to decompose 765 g of PCl₃

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Open Question

What is the heat of combustion of ethane, C₂H₆, in kilojoules per mole of ethane? Enthalpy of formation values can be found in this list of thermodynamic properties.

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Open Question

Use standard enthalpies of formation to calculate δh∘rxn for the following reaction: 2 H₂S(g) + 3 O₂(g)→ 2 H₂O(l) + 2SO₂(g)

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Open Question

Calculate the enthalpy of the reaction 2NO(g) + O₂(g) → 2NO₂(g)

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Open Question

Use the molar bond enthalpy data in the table to estimate the value of

δ𝐻°_rxn for the equation C₂H₄(g) + HBr(g) ⟶ C₅H₅Br(g)

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Open Question

Use standard enthalpies of formation to calculate δh∘rxn for the following reaction: Cao(s) + CO₂(g) → CaCO₃(s)

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Open Question

Calculate the enthalpy change for the reaction P₄O₆(s)+2 O₂(g) → P₄O₁₀(s)

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Open Question

For which one of the following is the enthalpy of the reaction the same as the enthalpy of formation?

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Open Question

Use the molar bond enthalpy data in the table to estimate the value of δ𝐻∘rxn for the equation

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Open Question

Use the values of δhf° in appendix 4 to calculate δh° for the following reactions.

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Open Question

For which one of the following reactions is δh°rxn equal to the heat of formation of the product?

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Open Question

Use the standard reaction enthalpies given below to determine δh°rxn for the following reaction:

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Open Question

Calculate the heat evolved per mole on combustion of each substance to yield co2(g) and h2o(g).

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Open Question

Calculate δs∘rxn for the following reaction. the δs∘ for each species is shown below the reaction.

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Open Question

Calculate delta h for the following reaction

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Open Question

Calculate the enthalpy of the reaction 2NO(g) + O₂(g) → 2NO₂(g) given the following reactions and enthalpies of formation: 1/2N₂(g) + O₂(g) → NO₂(g), ΔH^∘_a=33.2 kJ 1/2N₂(g) + 1/2O₂(g) → NO(g), ΔH^∘_b=90.2 kJ