Chapter 5: Problem 59
What is the connection between Hess's law and the fact that \(H\) is a state function?
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Chapter 5: Problem 59
What is the connection between Hess's law and the fact that \(H\) is a state function?
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The enthalpy change for melting ice at \(0{ }^{\circ} \mathrm{C}\) and constant atmospheric pressure is \(6.01 \mathrm{~kJ} / \mathrm{mol}\). Calculate the quantity of energy required to melt a moderately large iceberg with a mass of \(1.25\) million metric tons. (A metric ton is \(1000 \mathrm{~kg}\).)
You are given \(\Delta H\) for a process that occurs at constant pressure. What additional information do you need to determine \(\Delta E\) for the process?
Without referring to tables, predict which of the following has the higher enthalpy in each case: (a) \(1 \mathrm{~mol} \mathrm{CO}_{2}(\mathrm{~s})\) or \(1 \mathrm{~mol} \mathrm{CO}_{2}(g)\) at the same temperature, (b) \(2 \mathrm{~mol}\) of hydrogen atoms or \(1 \mathrm{~mol}\) of \(\mathrm{H}_{2}\) (c) \(1 \mathrm{~mol} \mathrm{H}_{2}(\mathrm{~g})\) and \(0.5 \mathrm{~mol}\) \(\mathrm{O}_{2}(g)\) at \(25^{\circ} \mathrm{C}\) or \(1 \mathrm{~mol} \mathrm{H}_{2} \mathrm{O}(g)\) at \(25^{\circ} \mathrm{C}\), (d) \(1 \mathrm{~mol} \mathrm{~N}_{\mathbf{2}}(g)\) at \(100^{\circ} \mathrm{C}\) or \(1 \mathrm{~mol} \mathrm{~N}_{2}(g)\) at \(300^{\circ} \mathrm{C}\).
Burning methane in oxygen can produce three different carbon-containing products: soot (very fine particles of graphite), \(\mathrm{CO}(\mathrm{g})\), and \(\mathrm{CO}_{2}(\mathrm{~g})\). (a) Write three balanced equations for the reaction of methane gas with oxygen to produce these three products. In each case assume that \(\mathrm{H}_{2} \mathrm{O}(l)\) is the only other product. (b) Determine the standard enthalpies for the reactions in part (a). (c) Why, when the oxygen supply is adequate, is \(\mathrm{CO}_{2}(g)\) the predominant carbon- containing product of the combustion of methane?
Consider the following reaction: $$ \mathrm{CH}_{3} \mathrm{OH}(g) \longrightarrow \mathrm{CO}(g)+2 \mathrm{H}_{2}(g) \quad \Delta H=+90.7 \mathrm{~kJ} $$ (a) Is heat absorbed or released in the course of this reaction? (b) Calculate the amount of heat transferred when \(45.0 \mathrm{~g}\) of \(\mathrm{CH}_{3} \mathrm{OH}(g)\) is decomposed by this reaction at constant pressure. (c) For a given sample of \(\mathrm{CH}_{3} \mathrm{OH}\), the enthalpy change on reaction is \(25.8 \mathrm{~kJ}\). How many grams of hydrogen gas are produced? What is the value of \(\Delta H\) for the reverse of the previous reaction? (d) How many kilojoules of heat are released when \(50.9 \mathrm{~g}\) of \(\mathrm{CO}(g)\) reacts completely with \(\mathrm{H}_{2}(g)\) to form \(\mathrm{CH}_{3} \mathrm{OH}(g)\) at constant pressure?
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