8. Thermochemistry

Thermochemical Equations

8. Thermochemistry

Thermochemical Equations

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Thermochemical Equations

Thermochemical Equations

Thermochemical Equations Example 1

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Practice this topic

Multiple Choice

Nitromethane (CH₃NO₂), sometimes used as a fuel for drag racing, burns according to the following reaction:

4 CH₃NO₂ (l) + 7 O₂ (g) → 4 CO₂ (g) + 6 H₂O (g) + 4 NO₂ (g) ∆Hº = – 2441.6 kJ

How much heat is released by burning 125.0 g of nitromethane (MW:61.044 g/mol)?

Consider the following reaction:

2 C₆H₆ (l) + 15 O₂ (g) → 12 CO₂ (g) + 6 H₂O (g) ∆Hº = – 6278 kJ

What volume of benzene (C₆H₆, d = 0.880 g/mL, molar mass = 78.11 g/mol) is necessary to evolve 5.19 x 10⁹ kJ of heat?

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Multiple Choice

The creation of liquid methanol is accomplished by the hydrogenation of carbon monoxide:

CO (g) + 2 H₂ (g) → CH₃OH (l) ∆Hº = – 128.1 kJ

How much heat (in kJ) is released when 125.0 g CO reacts with 2.32 x 10² g H₂?

Consider two identical iron nails: One nail is heated to 95℃, the other is cooled to 15℃. The two nails are placed in a coffee cup calorimeter and the system is allowed to come to thermal equilibrium. What is the final temperature of the two nails?

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Textbook Question

Isooctane is the primary component of gasoline and burns in air to produce water rand carbon dioxide 2 C8H18(g) + 25 O2(g) → 16 CO2(g) + 18 H2O(l) ΔH°= —10,940 kJ How much energy is released if 100.0 mL of isooctane (density = 0.690 g/mL) are burned (a) 3300 kJ (b) 6620 kJ (c) 6950 kJ (d) 3.02 kJ

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Textbook Question

Consider the following reaction: 2 CH3OH1g2¡ 2 CH41g2 + O21g2 H = +252.8 kJ (d) How many kilojoules of heat are released when 38.5 g of CH41g2 reacts completely with O21g2 to form CH3OH1g2 at constant pressure?

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Textbook Question

Consider the following reaction: 2 CH3OH1g2¡ 2 CH41g2 + O21g2 H = +252.8 kJ (b) Calculate the amount of heat transferred when 24.0 g of CH3OH1g2 is decomposed by this reaction at constant pressure.

When solutions containing silver ions and chloride ions are mixed, silver chloride precipitates Ag+1aq2 + Cl-1aq2 ¡ AgCl1s2 H = -65.5 kJ (a) Calculate H for the production of 0.450 mol of AgCl by this reaction. (b) Calculate H for the production of 9.00 g of AgCl. (c) Calculate H when 9.25 * 10-4 mol of AgCl dissolves in water.

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Textbook Question

At one time, a common means of forming small quantities of oxygen gas in the laboratory was to heat KClO3: 2 KClO31s2¡2 KCl1s2 + 3 O21g2 H = -89.4 kJ For this reaction, calculate H for the formation of (b) 10.4 g of KCl.

Consider the decomposition of liquid benzene, C6H61l2, to gaseous acetylene, C2H21g2: C6H61l2 ¡ 3 C2H21g2 H = +630 kJ (b) What is H for the formation of 1 mol of acetylene?

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Textbook Question

What mass of natural gas (CH4) must burn to emit 267 kJ of heat? CH4( g) + 2 O2( g)¡CO2( g) + 2 H2O( g) ΔH °rxn = -802.3 kJ

Nitromethane (CH3NO2) burns in air to produce significant amounts of heat. 2 CH3NO2(l ) + 32 O2( g)¡2 CO2( g) + 3 H2O(l ) + N2( g) ΔH °rxn = -1418 kJ How much heat is produced by the complete reaction of 5.56 kg of nitromethane?

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Textbook Question

Titanium reacts with iodine to form titanium(III) iodide, emitting heat. 2 Ti(s) + 3 I2( g)¡2 TiI3(s) ΔH °rxn = -839 kJ Determine the mass of titanium that react if 1.55 * 103 kJ of heat is emitted by the reaction.

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Textbook Question

The propane fuel (C3H8) used in gas barbeques burns according to the thermochemical equation: C3H8( g) + 5 O2( g)¡3 CO2( g) + 4 H2O( g) ΔH °rxn = -2044 kJ If a pork roast must absorb 1.6 * 103 kJ to fully cook, and if only 10% of the heat produced by the barbeque is actually absorbed by the roast, what mass of CO2 is emitted into the atmosphere during the grilling of the pork roast?

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Textbook Question

Charcoal is primarily carbon. Determine the mass of CO2 produced by burning enough carbon (in the form of charcoal) to produce 5.00 * 102 kJ of heat. C(s) + O2( g)¡CO2( g) ΔH °rxn = -393.5 kJ

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Textbook Question

The familiar "ether" used as an anesthetic agent is diethly ether, C4H10O. Its heat of vaporization is +26.5 kJ/mol at Calorimetry and Heat Capacity (Section 9.7) 9.76 What is the difference between heat capacity and specific heat? 9.77 Does a measurement carried out in a bomb calorimeter give its boiling point. How much energy in kilojoules is required to convert 100 mL of diethyl ether at its boiling point from liquid to vapor if its density is 0.7138 g/mL?

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Textbook Question

How much energy in kilojoules is required to convert 100 mL of water at its boiling point from liquid to vapor, and how does this compare with the result calculated in Problem 9.68 for diethyl ehter? [ΔHvap(H2O) = + 40.7 kJ/mol]

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Textbook Question

Aluminum metal reacts wiht chlorine with a spectacular display of sparks: 2 Al(s) + 3 Cl2(g) → 2 AlCl3(s) ΔH° = -1408.4 kJ How much heat in kilojoules is released on reaction of 5.00 g of Al?

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Textbook Question

How much heat in kilojoules is evolved or absorbed in the reaction of 1.00 g of Na with H2O? Is the reaction exother- mic or endothermic? 2 Na(s) + 2 H2O(l) → 2 NaOH(aq) + H2(g) ΔH° = -368.4 kJ

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Textbook Question

How much heat in kilojoules is evolved or absorbed in each of the following reactions?(b) Reaciton of 4.88 g of barium hydroxid eoctahydrate with ammonium chloride: Ba(OH)2·8 H2O (s) + 2 NH4Cl (s) → BaCl2(aq) + 2 NH3(aq) + 10 H2O(l) ΔH° = +80.3 kJ

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Textbook Question

How much heat in kilojoules is evolved or absorbed in each of the following reactions? (a) Burning of 15.5 g of propane: C3H8 (g) + 5 O2(g) → 3 CO2(g) + 4 H2O (l) ΔH°=-2220 kJ

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Textbook Question

The combustion of one mole of liquid octane, CH3(CH2)6CH3, produces 5470 kJ of heat. Calculate how much heat is produced if 1.000 gallon of octane is combusted. See Exercise 3.68 for necessary information about octane.

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Textbook Question

Nitromethane (CH3NO2), sometimes used as a fuel in drag racers, burns according to the following equation. How much heat is released by burning 100.0 g of nitromethane? 4 CH3NO2(l) + 7 O2(g) → 4 CO2(g) + 6 H2O(g) + 4 NO2(g) ΔH° = -2441.6 kJ

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Textbook Question

How much heat in kilojoules is evolved or absorbed in the reaction of 2.50 g Fe2O3 with enough carbon monoxide to produce iron metal? Is the process exothermic or endothermic? Fe2O3(s) + 3 CO2(g) → 2 Fe(s) + 3 CO2(g) ΔH° = -24.8 kJ

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Textbook Question

How much heat in kilojoules is evolved or absorbed in the reaction of 233.0 g of calcium oxide with enough carbon to produce calcium carbide? Is the process exothermic or endothermic? CaO(s) + 3 C(s) → CaC2(s) + CO(g) ΔH° = 464.6 kJ

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Textbook Question

Methanol 1CH3OH2 is used as a fuel in race cars. (d) Calculate the mass of CO2 produced per kJ of heat emitted.

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Textbook Question

Methanol 1CH3OH2 is used as a fuel in race cars. (c) Calculate the heat produced by combustion per liter of methanol. Methanol has a density of 0.791 g>mL.

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Textbook Question

Assume that 100.0 mL of 0.200 M CsOH and 50.0 mL of 0.400 M HCl are mixed in a calorimeter. The solutions start out at 22.50 °C, and the final temperature after reaction is 24.28 °C. The densities of the solutions are all 1.00 g/mL, and the specific heat of the mixture is 4.2 J/(g•°C). What is the enthalpy change for the neutralization reaction of 1.00 mol of CsOH in kJ?

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Textbook Question

Determine the mass of CO2 produced by burning enough of each fuel to produce 1.00 * 102 kJ of heat. a. CH4( g) + 2 O2( g)¡CO2( g) + 2 H2O( g) ΔH °rxn = -802.3 kJ

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Textbook Question

Liquid butane (C4H10) is stored in cylinders to be used as a fuel. The normal boiling point of butane is listed as -0.5 °C. (c) How much heat must be added to vaporize 250 g of butane if its heat of vaporization is 21.3 kJ/mol? What volume does this much butane occupy at 755 torr and 35 °C?

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Textbook Question

At the end of 2012, global population was about 7.0 billion people. What mass of glucose in kg would be needed to provide 1500 Cal/person/day of nourishment to the global population for one year? Assume that glucose is metabolized entirely to CO21g2 and H2O1l2 according to the following thermochemical equation: C6H12O61s2 + 6 O21g2¡6 CO21g2 + 6 H2O1l2 H = -2803 kJ

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Textbook Question

The automobile fuel called E85 consists of 85% ethanol and 15% gasoline. E85 can be used in the so-called flex-fuel vehicles (FFVs), which can use gasoline, ethanol, or a mix as fuels. Assume that gasoline consists of a mixture of octanes (different isomers of C8H18), that the average heat of combustion of C8H181l2 is 5400 kJ>mol, and that gasoline has an average density of 0.70 g>mL. The density of ethanol is 0.79 g>mL. (a) By using the information given as well as data in Appendix C, compare the energy produced by combustion of 1.0 L of gasoline and of 1.0 L of ethanol.