Log out Go to App
Go to App

Learning Materials

Features

Discover

Chapter 6: Problem 111

At \(298 \mathrm{~K}\), the standard enthalpies of formation for \(\mathrm{C}_{2} \mathrm{H}_{2}(\mathrm{~g})\) and \(\mathrm{C}_{6} \mathrm{H}_{6}(l)\) are \(227 \mathrm{~kJ} / \mathrm{mol}\) and \(49 \mathrm{~kJ} / \mathrm{mol}\), respectively. a. Calculate \(\Delta H^{\circ}\) for $$ \mathrm{C}_{6} \mathrm{H}_{6}(l) \longrightarrow 3 \mathrm{C}_{2} \mathrm{H}_{2}(g) $$ b. Both acetylene \(\left(\mathrm{C}_{2} \mathrm{H}_{2}\right)\) and benzene \(\left(\mathrm{C}_{6} \mathrm{H}_{6}\right)\) can be used as fuels. Which compound would liberate more energy per gram when combusted in air?

Short Answer

Expert verified
a. The ∆H° for the given reaction C6H6(l) → 3 C2H2(g) is 632 kJ/mol. b. Acetylene (C2H2) releases more energy per gram (8.72 kJ/g) when combusted in air than benzene (C6H6) (0.63 kJ/g).

Step by step solution

01

Write the general formula for calculating ∆H°

Recalling the formula for ∆H° of reaction: ∆H°(reaction) = Σn∆H°f(products) - Σm∆H°f(reactants) Where n and m are the stoichiometric coefficients of the products and reactants, respectively, and ∆H°f represents their standard enthalpies of formation.
02

Apply the formula to the given reaction

For the reaction: C6H6(l) → 3 C2H2(g) ∆H°(reaction) = 3*(∆H°f(C2H2(g))) - (∆H°f(C6H6(l))) Using the given data: ∆H°f(C2H2) = 227 kJ/mol and ∆H°f(C6H6) = 49 kJ/mol ∆H°(reaction) = 3*(227 kJ/mol) - 49 kJ/mol
03

Calculate ∆H°(reaction)

Calculating the value of ∆H°(reaction): ∆H°(reaction) = 681 kJ/mol - 49 kJ/mol ∆H°(reaction) = 632 kJ/mol a. The ∆H° for the given reaction C6H6(l) → 3 C2H2(g) is 632 kJ/mol b. Identify the compound that liberates more energy per gram when combusted in air
04

Calculate the molar mass of C2H2 and C6H6

The molar mass of C2H2 is 2*12.01 g/mol (C) + 2*1.01 g/mol (H) = 26.04 g/mol The molar mass of C6H6 is 6*12.01 g/mol (C) + 6*1.01 g/mol (H) = 78.12 g/mol
05

Calculate the energy released per gram for each compound

Energy per gram for C2H2: (∆H°f(C2H2) / Molar mass of C2H2) = (227 kJ/mol) / (26.04 g/mol) Energy per gram for C6H6: (∆H°f(C6H6) / Molar mass of C6H6) = (49 kJ/mol) / (78.12 g/mol)
06

Compare the energy per gram values

Energy per gram for C2H2: 8.72 kJ/g Energy per gram for C6H6: 0.63 kJ/g Comparing the energy per gram values, we find that C2H2 releases more energy per gram (8.72 kJ/g) when combusted in air than C6H6 (0.63 kJ/g).

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Start your free trial

Over 30 million students worldwide already upgrade their learning with Vaia!

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

Consider the reaction \(2 \mathrm{HCl}(a q)+\mathrm{Ba}(\mathrm{OH})_{2}(a q) \longrightarrow \mathrm{BaCl}_{2}(a q)+2 \mathrm{H}_{2} \mathrm{O}(l)\) \(\Delta H=-118 \mathrm{~kJ}\) Calculate the heat when \(100.0 \mathrm{~mL}\) of \(0.500 \mathrm{M} \mathrm{HCl}\) is mixed with \(300.0 \mathrm{~mL}\) of \(0.100 \mathrm{M} \mathrm{Ba}(\mathrm{OH})_{2}\). Assuming that the temperature of both solutions was initially \(25.0^{\circ} \mathrm{C}\) and that the final mixture has a mass of \(400.0 \mathrm{~g}\) and a specific heat capacity of \(4.18 \mathrm{~J} /{ }^{\circ} \mathrm{C} \cdot \mathrm{g}\), calculate the final temperature of the mixture.

The standard enthalpy of combustion of ethene gas, \(\mathrm{C}_{2} \mathrm{H}_{4}(\mathrm{~g})\), is \(-1411.1 \mathrm{~kJ} / \mathrm{mol}\) at \(298 \mathrm{~K}\). Given the following enthalpies of formation, calculate \(\Delta H_{\mathrm{f}}^{\circ}\) for \(\mathrm{C}_{2} \mathrm{H}_{4}(\mathrm{~g})\). $$ \begin{array}{ll} \mathrm{CO}_{2}(g) & -393.5 \mathrm{~kJ} / \mathrm{mol} \\ \mathrm{H}_{2} \mathrm{O}(l) & -285.8 \mathrm{~kJ} / \mathrm{mol} \end{array} $$

Liquid water turns to ice. Is this process endothermic or exothermic? Explain what is occurring using the terms system, surroundings, heat, potential energy, and kinetic energy in the discussion.

The enthalpy of combustion of solid carbon to form carbon dioxide is \(-393.7 \mathrm{~kJ} / \mathrm{mol}\) carbon, and the enthalpy of combustion of carbon monoxide to form carbon dioxide is \(-283.3 \mathrm{~kJ} /\) mol CO. Use these data to calculate \(\Delta H\) for the reaction $$ 2 \mathrm{C}(s)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{CO}(g) $$

In which of the following systems is(are) work done by the surroundings on the system? Assume pressure and temperature are constant. a. \(2 \mathrm{SO}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{SO}_{3}(g)\) b. \(\mathrm{CO}_{2}(s) \longrightarrow \mathrm{CO}_{2}(g)\) c. \(4 \mathrm{NH}_{3}(g)+7 \mathrm{O}_{2}(g) \longrightarrow 4 \mathrm{NO}_{2}(g)+6 \mathrm{H}_{2} \mathrm{O}(g)\) d. \(\mathrm{N}_{2} \mathrm{O}_{4}(g) \longrightarrow 2 \mathrm{NO}_{2}(g)\) e. \(\mathrm{CaCO}_{3}(s) \longrightarrow \mathrm{CaCO}(s)+\mathrm{CO}_{2}(g)\)
See all solutions

Recommended explanations on Chemistry Textbooks

Chemical Analysis

Read Explanation

Organic Chemistry

Read Explanation

Making Measurements

Read Explanation

Kinetics

Read Explanation

Nuclear Chemistry

Read Explanation

The Earths Atmosphere

Read Explanation
View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.

Sign-up for free