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Chapter 6: Problem 120

From the enthalpy of formation for \(\mathrm{CO}_{2}\) and the following information, calculate the standard enthalpy of formation for carbon monoxide (CO). $$ \begin{aligned} \mathrm{CO}(g)+\frac{1}{2} \mathrm{O}_{2}(g) & \longrightarrow \mathrm{CO}_{2}(g) \\ \Delta H^{\circ} &=-283.0 \mathrm{~kJ} / \mathrm{mol} \end{aligned} $$Why can't we obtain it directly by measuring the enthalpy of the following reaction?$$\mathrm{C}(\text { graphite })+\frac{1}{2} \mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}(g)$$

Short Answer

Expert verified
The standard enthalpy of formation for carbon monoxide (CO) is -110.5 kJ/mol. The direct measurement cannot be made due to the difficulty in controlling the reaction conditions and accurately measuring the heat change.

Step by step solution

01

Understanding the given information

We know that the standard enthalpy of formation for CO2 (ΔHf°(CO2)) is -393.5 kJ/mol. We also know that when CO reacts with O2 to form CO2, the resultant energy change (ΔH°) is -283.0 kJ/mol.
02

Applying Hess’s Law to determine the enthalpy of formation for CO

We can determine the enthalpy of formation of CO (ΔHf°CO) by creating a reaction cycle. First, the formation of CO2 from its constituent elements is: \(C(graphite) + O_{2}(g) \rightarrow CO_{2}(g)\) with ΔH° = ΔHf°(CO2) = -393.5 kJ/mol. And the backward reaction of CO2 to CO and O2 is: \(CO_{2}(g) \rightarrow CO(g) + \frac{1}{2}O_{2}(g)\) with ΔH° = 283.0 kJ/mol. Since the total enthalpy change in a cycle is zero by Hess’s Law, we can add these two reactions to find ΔHf°(CO). Therefore, ΔHf°(CO) = ΔHf°(CO2) + 283.0 kJ/mol. By substituting the known values, ΔHf°(CO) = -393.5 kJ/mol + 283.0 kJ/mol = -110.5 kJ/mol

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Most popular questions from this chapter

Explain the cooling effect experienced when ethanol is rubbed on your skin, given that $$\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(l) \longrightarrow \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(g) \quad \Delta H^{\circ}=42.2 \mathrm{~kJ} / \mathrm{mol}$$

A driver's manual states that the stopping distance quadruples as the speed doubles; that is, if it takes \(30 \mathrm{ft}\) to stop a car moving at \(25 \mathrm{mph}\) then it would take \(120 \mathrm{ft}\) to stop a car moving at \(50 \mathrm{mph}\). Justify this statement by using mechanics and the first law of thermodynamics. [Assume that when a car is stopped, its kinetic energy \(\left(\frac{1}{2} m u^{2}\right)\) is totally converted to heat.]

What are the units for energy commonly employed in chemistry?

lime is a term that includes calcium oxide (CaO, also called quicklime) and calcium hydroxide \(\left[\mathrm{Ca}(\mathrm{OH})_{2},\right.\) also called slaked lime \(] .\) It is used in the steel industry to remove acidic impurities, in airpollution control to remove acidic oxides such as \(\mathrm{SO}_{2}\), and in water treatment. Quicklime is made industrially by heating limestone \(\left(\mathrm{CaCO}_{3}\right)\) above \(2000^{\circ} \mathrm{C}:\) $$ \begin{array}{r} \mathrm{CaCO}_{3}(s) \longrightarrow \mathrm{CaO}(s)+\mathrm{CO}_{2}(g) \\ \Delta H^{\circ}=177.8 \mathrm{~kJ} / \mathrm{mol} \end{array} $$ Slaked lime is produced by treating quicklime with water: $$ \begin{array}{r} \mathrm{CaO}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{Ca}(\mathrm{OH})_{2}(s) \\ \Delta H^{\circ}=-65.2 \mathrm{~kJ} / \mathrm{mol} \end{array} $$ The exothermic reaction of quicklime with water and the rather small specific heats of both quicklime \(\left(0.946 \mathrm{~J} / \mathrm{g} \cdot{ }^{\circ} \mathrm{C}\right)\) and slaked lime \(\left(1.20 \mathrm{~J} / \mathrm{g} \cdot{ }^{\circ} \mathrm{C}\right)\) make it hazardous to store and transport lime in vessels made of wood. Wooden sailing ships carrying lime would occasionally catch fire when water leaked into the hold. (a) If a \(500-\mathrm{g}\) sample of water reacts with an equimolar amount of \(\mathrm{CaO}\) (both at an initial temperature of \(25^{\circ} \mathrm{C}\) ), what is the final temperature of the product, \(\mathrm{Ca}(\mathrm{OH})_{2} ?\) Assume that the product absorbs all of the heat released in the reaction. (b) Given that the standard enthalpies of formation of \(\mathrm{CaO}\) and \(\mathrm{H}_{2} \mathrm{O}\) are \(-635.6 \mathrm{~kJ} / \mathrm{mol}\) and \(-285.8 \mathrm{~kJ} / \mathrm{mol}\) respectively, calculate the standard enthalpy of formation of \(\mathrm{Ca}(\mathrm{OH})_{2}\)

These are various forms of energy: chemical, heat, light, mechanical, and electrical. Suggest ways of interconverting these forms of energy.
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