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Chapter 5: Problem 70

Write balanced equations that describe the formation of the following compounds from elements in their standard states, and then look up the standard enthalpy of formation for each substance in Appendix C: (a) \(\mathrm{CH}_{3} \mathrm{OH}(l),\) (b) \(\mathrm{CaSO}_{4}(s),\) (d) \(\mathrm{P}_{4} \mathrm{O}_{6}(s),\) (c) \(\mathrm{NO}(g)\).

Short Answer

Expert verified
Balanced equations and standard enthalpies of formation for compounds: a) Methanol (CH3OH): \[ C(s) + 2H_{2}(g) + \frac{1}{2}O_{2}(g) \rightarrow CH_{3}OH(l) \] ΔHf° = -238.7 kJ/mol b) Calcium sulfate (CaSO4): \[ Ca(s) + S(s) + 2O_{2}(g) \rightarrow CaSO_{4}(s) \] ΔHf° = -1434.5 kJ/mol c) Nitric oxide (NO): \[ \frac{1}{2}N_{2}(g) + \frac{1}{2}O_{2}(g) \rightarrow NO(g) \] ΔHf° = +90.3 kJ/mol d) Phosphorus trioxide (P4O6): \[ P_{4}(s) + 3O_{2}(g) \rightarrow P_{4}O_{6}(s) \] ΔHf° = -1640.1 kJ/mol

Step by step solution

01

Identify elements in standard states

Methanol (CH3OH) is composed of carbon, hydrogen, and oxygen. The standard states of these elements are: Carbon (C): solid Hydrogen (H2): gas Oxygen (O2): gas
02

Write the balanced equation

Consider an equation showing the formation of 1 mol of CH3OH from its elements in standard states. \[ C(s) + 2H_{2}(g) + \frac{1}{2}O_{2}(g) \rightarrow CH_{3}OH(l) \]
03

Look up the standard enthalpy of formation in Appendix C

From Appendix C, the standard enthalpy of formation, ΔHf°, for CH3OH(l) is -238.7 kJ/mol. #b. Writing a balanced equation for the formation of CaSO4 (s) from its elements in standard states#
04

Identify elements in standard states

Calcium sulfate (CaSO4) is composed of calcium, sulfur, and oxygen. The standard states of these elements are: Calcium (Ca): solid Sulfur (S): solid Oxygen (O2): gas
05

Write the balanced equation

Consider an equation showing the formation of 1 mol of CaSO4 from its elements in standard states. \[ Ca(s) + S(s) + 2O_{2}(g) \rightarrow CaSO_{4}(s) \]
06

Look up the standard enthalpy of formation in Appendix C

From Appendix C, the standard enthalpy of formation, ΔHf°, for CaSO4(s) is -1434.5 kJ/mol. #c. Writing a balanced equation for the formation of NO (g) from its elements in standard states#
07

Identify elements in standard states

Nitric oxide (NO) is composed of nitrogen and oxygen. The standard states of these elements are: Nitrogen (N2): gas Oxygen (O2): gas
08

Write the balanced equation

Consider an equation showing the formation of 1 mol of NO from its elements in standard states. \[ \frac{1}{2}N_{2}(g) + \frac{1}{2}O_{2}(g) \rightarrow NO(g) \]
09

Look up the standard enthalpy of formation in Appendix C

From Appendix C, the standard enthalpy of formation, ΔHf°, for NO(g) is +90.3 kJ/mol. #d. Writing a balanced equation for the formation of P4O6 (s) from its elements in standard states#
10

Identify elements in standard states

Phosphorus trioxide (P4O6) is composed of phosphorus and oxygen. The standard states of these elements are: Phosphorus (P4): solid Oxygen (O2): gas
11

Write the balanced equation

Consider an equation showing the formation of 1 mol of P4O6 from its elements in standard states. \[ P_{4}(s) + 3O_{2}(g) \rightarrow P_{4}O_{6}(s) \]
12

Look up the standard enthalpy of formation in Appendix C

From Appendix C, the standard enthalpy of formation, ΔHf°, for P4O6(s) is -1640.1 kJ/mol.

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Most popular questions from this chapter

Sucrose \(\left(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\right)\) is produced by plants as follows: $$ \begin{aligned} 12 \mathrm{CO}_{2}(g)+11 \mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}+12 \mathrm{O}_{2}(g) \\ \Delta H=5645 \mathrm{~kJ} \end{aligned} $$ About \(4.8 \mathrm{~g}\) of sucrose is produced per day per square meter of the earth's surface. The energy for this endothermic reaction is supplied by the sunlight. About \(0.1 \%\) of the sunlight that reaches the earth is used to produce sucrose. Calculate the total energy the sun supplies for each square meter of surface area. Give your answer in kilowatts per square meter \(\left(\mathrm{kW} / \mathrm{m}^{2}\right.\) where $\left.1 \mathrm{~W}=1 \mathrm{~J} / \mathrm{s}\right).$

For the following processes, calculate the change in internal energy of the system and determine whether the process is endothermic or exothermic: (a) A balloon is cooled by removing \(0.655 \mathrm{~kJ}\) of heat. It shrinks on cooling, and the atmosphere does \(382 \mathrm{~J}\) of work on the balloon. (b) A 100.0-g bar of gold is heated from \(25^{\circ} \mathrm{C}\) to \(50^{\circ} \mathrm{C}\) during which it absorbs \(322 \mathrm{~J}\) of heat. Assume the volume of the gold bar remains constant.

Under constant-volume conditions, the heat of combustion of sucrose \(\left(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\right)\) is $16.49 \mathrm{~kJ} / \mathrm{g}\(. A \)3.00-\mathrm{g}$ sample of sucrose is burned in a bomb calorimeter. The temperature of the calorimeter increases from 21.94 to \(24.62^{\circ} \mathrm{C} .(\mathbf{a})\) What is the total heat capacity of the calorimeter? (b) If the size of the sucrose sample had been exactly twice as large, what would the temperature change of the calorimeter have been?

At one time, a common means of forming small quantities of oxygen gas in the laboratory was to heat \(\mathrm{KClO}_{3}\) : $$ 2 \mathrm{KClO}_{3}(s) \longrightarrow 2 \mathrm{KCl}(s)+3 \mathrm{O}_{2}(g) \quad \Delta H=-89.4 \mathrm{~kJ} $$ For this reaction, calculate \(\Delta H\) for the formation of (a) $1.36 \mathrm{~mol}\( of \)\mathrm{O}_{2}\( and \)(\mathbf{b}) 10.4 \mathrm{~g}$ of \(\mathrm{KCl} .(\mathbf{c})\) The decomposition of \(\mathrm{KClO}_{3}\) proceeds spontaneously when it is heated. Do you think that the reverse reaction, the formation of \(\mathrm{KClO}_{3}\) from \(\mathrm{KCl}\) and \(\mathrm{O}_{2},\) is likely to be feasible under ordinary conditions? Explain your answer.

The heat of combustion of ethanol, $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(l),\( is -1367 \)\mathrm{kJ} / \mathrm{mol}$. A bottle of stout (dark beer) contains up to \(6.0 \%\) ethanol by mass. Assuming the density of the beer to be \(1.0 \mathrm{~g} / \mathrm{mL},\) what is the caloric content due to the alcohol (ethanol) in a bottle of beer \((500 \mathrm{~mL})\) ?
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