Chapter 21, Problem 72PS

Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074

Chapter
Section

Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074
Textbook Problem

A sulfuric acid plant produces an enormous amount of heat. To keep costs as low as possible, much of this heat is used to make steam to generate electricity. Some of the electricity is used to run the plant, and the excess is sold to the local electrical utility. Three reactions are important in sulfuric acid production: (1) burning S to SO2; (2) oxidation of SO2 to SO3; and (3) reaction of SO3 with H2O: SO 3 ( g ) +  H 2 O (in 98% H 2 SO 4 )  →  H 2 SO 4 ( l ) The enthalpy change of the third reaction is −130 kJ/mol. Estimate the enthalpy change when 1.00 mol of S is used to produce 1.00 mol of H2SO4. How much energy is produced per metric ton (1.00 × 103 kg) of H2SO4?

Interpretation Introduction

Interpretation:

To calculate enthalpy change when one mole of sulfur produced one mole of sulfuric acid and energy produced per metric ton of sulfuric acid is to be stated.

Concept introduction:

The amount of heat released or absorbed in a chemical reaction under constant pressure is known as enthalpy change. It is denoted by ΔH.

The enthalpy change of any reaction is written as,

ΔH=ΔfHproductsΔfHreactants                                 (1)

Enthalpy of formation is ithe enthalpy change when one mole of a compound is formed from its elements.

Numberofmoles=MassMolecularmass

Explanation

The enthalpy change of one mole of sulfur produced one mole of sulfuric acid and energy produced per matric ton of sulfuric acid is calculated below.

Given:

The mass of sulphuric acid per matric ton is 106â€‰g.

The molar mass of sulphuric acid is 98â€‰gâ‹…molâˆ’1.

Refer to the appendix L for enthalpy values.

The enthalpy of formation (Î”fH) of water is âˆ’285.83â€‰kJâ‹…molâˆ’1.

For the production of sulfuric acid from sulfur atom, three reactions are involved. The first reaction is production of sulfur dioxide from sulfur atom is written as,

Â Â Â Â S(s)+O2(g)â†’SO2(g) (2)

The heat of formation (Î”fH) of SO2 is âˆ’296.84â€‰kJâ‹…molâˆ’1. Since, enthalpy of formation of substance which present in its elemental form in the reaction is zero. Hence, enthalpy change of sulfur dioxide is equal to the heat of formation of sulfur dioxide.

The second reaction is production of SO3 from SO2 is written as,

Â Â Â Â SO2(g)+12O2(g)â†’SO3(g)Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â  (3)

The enthalpy change of above reaction is âˆ’98â€‰kJâ‹…molâˆ’1.

The final reaction is production sulphuric acid is written as follows,

Â Â Â Â SO3(g)+H2O(l)â†’H2SO4(l)Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â  (4)

The enthalpy change (Î”H) of this reaction is âˆ’130â€‰kJâ‹…molâˆ’1

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