/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 121 The standard enthalpies of forma... [FREE SOLUTION] | 91影视

91影视

Log out

Learning Materials

Features

Discover

Chapter 5: Problem 121

The standard enthalpies of formation of benzene \(C_{6} \mathrm{H}_{6}(\ell)\) \(\mathrm{CO}_{2}(g),\) and \(\mathrm{H}_{2} \mathrm{O}(\ell)\) are \(49.0,-394,\) and \(-286 \mathrm{kJ} / \mathrm{mol}\) respectively. Use this information to calculate the standard enthalpy of combustion of \(\mathrm{C}_{6} \mathrm{H}_{6}(\ell)\)

Short Answer

Expert verified
Question: Calculate the standard enthalpy of combustion for benzene, given the standard enthalpy of formation for benzene (\(C_6H_6(\ell)\)) is 49 kJ/mol, carbon dioxide (\(CO_2(g)\)) is -394 kJ/mol, and water (\(H_2O(\ell)\)) is -286 kJ/mol. Answer: The standard enthalpy of combustion for benzene is -2809 kJ/mol.

Step by step solution

01

Write the combustion reaction

The combustion reaction of benzene is: \(C_6H_6(\ell) + \frac{15}{2}O_2(g) \rightarrow 6CO_2(g) + 3H_2O(\ell)\)
02

Calculate the enthalpy change of products

Sum of the enthalpies of products: \(6 \times \Delta H_{CO_2} + 3 \times \Delta H_{H_2O} = 6 \times (-394\, kJ/mol) + 3 \times (-286\, kJ/mol) = -2760 \,kJ\)
03

Calculate the enthalpy change of reactants

Sum of the enthalpies of reactants (we don't consider \(O_2\) because its enthalpy of formation is 0): \(\Delta H_{benzene} = 49\, kJ/mol\)
04

Calculate the standard enthalpy of combustion

Applying Hess's Law: \(\Delta H_{combustion} = \Delta H_{products} - \Delta H_{reactants} = -2760\, kJ - 49\, kJ = -2809 \,kJ/mol\) The standard enthalpy of combustion for benzene is -2809 kJ/mol.

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.

Over 30 million students worldwide already upgrade their learning with 91影视!

Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Enthalpy of Formation
Enthalpy of formation refers to the heat change when one mole of a compound forms from its elements in their standard states. These standard states are at 1 atm and usually 25掳C. For example, the enthalpy of formation for
  • Carbon dioxide (\( \text{CO}_2(g) \) ): \(-394 \, \text{kJ/mol}\)
  • Water (\( \text{H}_2\text{O}(\ell) \) ): \(-286 \, \text{kJ/mol}\)
  • Benzene (\( \text{C}_6\text{H}_6(\ell) \) ): 49 \( \text{kJ/mol} \)
These values indicate whether the process absorbs or releases energy.
The negative sign reflects an exothermic process. An exothermic reaction releases heat, while a positive sign shows an endothermic process, which absorbs heat.
Understanding these values is crucial when calculating enthalpy changes in a reaction.
Hess's Law
Hess's Law is an essential principle in chemistry. It states that the total enthalpy change in a reaction is the same, no matter how it is carried out, as long as the initial and final conditions are the same.
This allows us to calculate the enthalpy change of a complex reaction using simpler steps or known reactions.
  • To find the enthalpy of combustion of benzene, we calculate all steps involved.
  • The products and reactants' standard enthalpies of formation help determine this value.
By applying Hess's Law:
The enthalpy of combustion equals the sum of the products' enthalpies minus the reactants' enthalpies. This provides the energy change when benzene combusts completely.
Chemical Reactions
Chemical reactions involve the transformation of reactants into products. During combustion, substances like benzene react with oxygen to form carbon dioxide and water.
This reaction releases energy, typically seen in the form of heat and light. The combustion of benzene can be shown in the equation:
  • \( \text{C}_6\text{H}_6(\ell) + \frac{15}{2}\text{O}_2(g) \rightarrow 6\text{CO}_2(g) + 3\text{H}_2\text{O}(\ell) \)
In this equation:
  • \( \text{C}_6\text{H}_6(\ell) \) represents benzene
  • \( \text{O}_2(g) \) is oxygen
  • The products are carbon dioxide and water
Understanding this reaction helps in calculating the enthalpy changes.It's a practical example of how chemical reactions are essential in energy exchange processes.

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

The standard enthalpy of combustion of benzoic acid (molar mass \(122 \mathrm{g} / \mathrm{mol}\) ) is \(-3225 \mathrm{kJ} / \mathrm{mol}\). Calculate the heat capacity of a bomb calorimeter if a temperature increase of \(2.16^{\circ} \mathrm{C}\) occurs on combusting \(0.500 \mathrm{g}\) of benzoic acid in the presence of excess \(\mathrm{O}_{2}\).

Adding \(1.56 \mathrm{g}\) of \(\mathrm{K}_{2} \mathrm{SO}_{4}\) to \(6.00 \mathrm{mL}\) of water at \(16.2^{\circ} \mathrm{C}\) causes the temperature of the solution to drop by \(7.70^{\circ} \mathrm{C}\) How many grams of \(\mathrm{NaOH}\left(\Delta H_{\text {soln }}=-44.3 \mathrm{kJ} / \mathrm{mol}\right)\) would you need to add to raise the temperature back to \(16.2^{\circ} \mathrm{C} ?\)

A solid with metallic properties is formed when hydrogen gas is compressed under extremely high pressures. Predict the sign of the enthalpy change for the following reaction: $$\mathrm{H}_{2}(g) \rightarrow \mathrm{H}_{2}(s)$$

Explosives called amatols are mixtures of ammonium nitrate and TNT introduced during World War I when TNT was in short supply. The mixtures can provide \(30 \%\) more explosive power than TNT alone. Above \(300^{\circ} \mathrm{C},\) ammonium nitrate decomposes to \(\mathrm{N}_{2}, \mathrm{O}_{2}\) and \(\mathrm{H}_{2} \mathrm{O} .\) Write a balanced chemical reaction describing the decomposition of ammonium nitrate, and determine the standard enthalpy of reaction by using the appropriate standard enthalpies of formation from Appendix 4.

Use the following standard heats of formation to calculate the molar enthalpy of vaporization of acetic acid: \(\Delta H_{\mathrm{f}}^{\circ}\) of \(\mathrm{CH}_{3} \mathrm{COOH}(\ell)\) is \(-484.5 \mathrm{~kJ} / \mathrm{mol}\) and \(\Delta H_{\mathrm{f}}^{\circ}\) of \(\mathrm{CH}_{3} \mathrm{COOH}(g)\) is \(-432.8 \mathrm{~kJ} / \mathrm{mol}\).
See all solutions

Recommended explanations on Chemistry Textbooks

Chemistry Branches

Read Explanation

Making Measurements

Read Explanation

Chemical Reactions

Read Explanation

Organic Chemistry

Read Explanation

The Earths Atmosphere

Read Explanation

Inorganic Chemistry

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.