MCGRAW: CHEMISTRY THE MOLECULAR NATURE
MCGRAW: CHEMISTRY THE MOLECULAR NATURE
8th Edition
ISBN: 9781264330430
Author: VALUE EDITION
Publisher: MCG
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Chapter 20, Problem 20.93P

(a)

Interpretation Introduction

Interpretation:

The given reaction has to be shown whether it is thermodynamically feasible or not.

Concept introduction:

Free energy (or) entropy change is the term that is used to explain the total energy content in a thermodynamic system that can be converted into work.  The free energy is represented by the letter G.  All spontaneous process is associated with the decrease of free energy in the system.  The equation given below helps us to calculate the change in free energy in a system.

  ΔGo = ΔΗo- TΔSo

Where,

  ΔGo is the standard change in free energy of the system

  ΔΗo is the standard change in enthalpy of the system

  T is the absolute value of the temperature

  ΔSo is the change in entropy in the system

(a)

Expert Solution
Check Mark

Answer to Problem 20.93P

Methanol formation standard free energy values is ΔGrxno=-29.2kJ_.

Explanation of Solution

The reaction for formation of methanol is,

  CO(g)+2H2(g)CH3OH(l)

Standard enthalpy change is,

The enthalpy change for the reaction is calculated as follows,

  ΔH°rxn = ΔH°f(Products)- nΔH°f(reactants)

  ΔH°rxn =[(1molCH3OH)(ΔH°fofCH3OH)][(1molCO)(ΔH°fofCO)+(2molH2)(ΔH°fofH2)]ΔH°rxn =[(1molCH3OH)(238.6kJ/mol)][(1molCO)(110.5kJ/mol)+(2molH2)(0kJ/mol)]ΔH°rxn =-128.1kJ

Hence, the enthalpy changes (ΔH°rxn) is -128.1kJ_ 

Entropy change  ΔS°system

Calculate the change in entropy for this reaction as follows,

  ΔS°rxn = S°Products- nS°reactants

Where, (m)and(n) are the stoichiometric co-efficient.

  ΔS°rxn =[(1molCH3OH)(SoofCH3OH)][(1molCO)(ΔS°rxnofCO)+(2molH2)(ΔS°rxnofH2)]ΔH°rxn =[(1molCH3OH)(127J/Kmol)][(1molCO)(197.5J/Kmol)+(2molH2)(130.6127J/Kmol)]ΔH°rxn =-331.7J/K

The (ΔS°rxn) of the reaction is -331.7J/K_ 

Calculate the Free enrgy change  ΔGrxno

Standared Free energy change equation iss,

  ΔGrxno = ΔΗrxno- TΔSrxno

Calcualted enthalpy and entropy  values are

  ΔΗrxno=-128.1kJΔSrxno=-331.7J/KT1=273+25=298K

These values are plugging above standard free energy equation,

         ΔGrxno=128.1kJ-[(298K)(331.7J/K)(1kJ/103)]=29.2534kJΔGrxno=-29.2kJ

Methanol formation standard free energy values is ΔGrxno=-29.2kJ_, the negative value of ΔGo indicates that the reaction is spontaneous and it is feasible. 

(b)

Interpretation Introduction

Interpretation:

The given methanol formation reaction has to be shown that whether it is favored at low or at high temperatures.

Concept introduction:

Any natural process or a chemical reaction taking place in a laboratory can be classified into two categories, spontaneous or nonspontaneous. Spontaneous process occurs by itself, without the influence of external energy. In spontaneous process the free energy of the system decreases and entropy of the system increases. Nonspontaneous process requires an external influence for initiation. In nonspontaneous process the free energy of the system increases but entropy in the system decreases.

In thermodynamics a process is spontaneous if it is taking place by itself without the help of external energy.  All spontaneous process will have highly energetic initial state than the final state. This indicates that while the process occurs, there is a decrease in free energy of the system. The increase in randomness also favors the spontaneity of a process.

(b)

Expert Solution
Check Mark

Explanation of Solution

The reaction for formation of methanol is,

  CO(g)+2H2(g)CH3OH(l)

Calcualted enthalpy and entropy  values are

  ΔΗrxno=-128.1kJΔSrxno=-331.7J/KT1=273+25=298K

At temprature become above 298K, this reaction is non-spontaneous. Because both enthalpy ΔΗrxno and entropy ΔSrxno values are negative, that means the reaction is favored at low temprature.

(c)

Interpretation Introduction

Interpretation:

For the given methanol oxidation reaction the ΔGo value has to calculate at 100oC.

Concept introduction:

Free energy (or) entropy change is the term that is used to explain the total energy content in a thermodynamic system that can be converted into work.  The free energy is represented by the letter G.  All spontaneous process is associated with the decrease of free energy in the system.  The equation given below helps us to calculate the change in free energy in a system.

  ΔGo = ΔΗo- TΔSo

Where,

  ΔGo is the standard change in free energy of the system

  ΔΗo is the standard change in enthalpy of the system

  T is the absolute value of the temperature

  ΔSo is the change in entropy in the system

(c)

Expert Solution
Check Mark

Answer to Problem 20.93P

Methanol oxidation reaction standard free energy values is ΔGrxno=-182kJ_

Explanation of Solution

The oxidation reaction of methanol is,

  CH3OH(g)+1/2O2(g)CH2O(g)+H2O(g)

Standard enthalpy change is,

The enthalpy change for the reaction is calculated as follows,

  ΔH°rxn = ΔH°f(Products)- nΔH°f(reactants)

  ΔH°rxn =[(1molCH2O)(ΔH°fofCH2O)+(1molH2O)(ΔH°fofH2O)][(1molCH3OH)(ΔH°fofCH3OH)+(1/2molO2)(ΔH°fofO2)]ΔH°rxn =[(1molCH2O)(116kJ/mol)+(1molH2O)(241.826kJ/mol)][(1molCH3OH)(201.2kJ/mol)+(1/2molO2)(0kJ/mol)]ΔH°rxn =-156.626kJ

Hence, the enthalpy changes (ΔH°rxn) is -156.626kJ_ 

Entropy changeΔS°system

Calculate the change in entropy for this reaction as follows,

  ΔS°rxn = S°Products- nS°reactants

Where, (m)and(n) are the stoichiometric co-efficient.

  ΔS°rxn =[(1molCH2O)(SoofCH2O)+(1molH2O)(SoofH2O)][(1molCH3OH)(ΔS°rxnofCH3OH)+(1/2molO2)(ΔS°rxnofO2)]ΔH°rxn =[(1molCH2O)(219J/Kmol)+(1molH2O)(188.72J/Kmol)][(1molCH3OH)(238J/Kmol)+(1/2molO2)(205.0J/Kmol)]ΔH°rxn =-67.22J/K

The (ΔS°rxn) of the reaction is -67.22J/K_

Calculate the Free enrgy changeΔGrxno

Standared Free energy change equation is,

  ΔGrxno = ΔΗrxno- TΔSrxno

Calculated enthalpy and entropy  values are

  ΔΗrxno=-156.626kJΔSrxno=-67.22J/KT1=273+100=373K

These values are plugging above standard free energy equation,

  ΔGrxno=156.626kJ-[(373K)(67.22J/K)(1kJ/103)]=181.699kJΔGrxno=-182kJ

Therefore, the given oxidation reaction standard free energy values is ΔGrxno=-182kJ_

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Chapter 20 Solutions

MCGRAW: CHEMISTRY THE MOLECULAR NATURE

Ch. 20.3 - Prob. 20.6AFPCh. 20.3 - Prob. 20.6BFPCh. 20.3 - Prob. 20.7AFPCh. 20.3 - Prob. 20.7BFPCh. 20.3 - Prob. 20.8AFPCh. 20.3 - Prob. 20.8BFPCh. 20.3 - Prob. B20.1PCh. 20.3 - Nonspontaneous processes like muscle contraction,...Ch. 20.4 - Use Appendix B to find K at 298 K for the...Ch. 20.4 - Use the given value of K to calculate ΔG° at 298 K...Ch. 20.4 - Prob. 20.10AFPCh. 20.4 - Prob. 20.10BFPCh. 20.4 - At 298 K, ΔG° = −33.5 kJ/mol for the formation of...Ch. 20.4 - Prob. 20.11BFPCh. 20 - Prob. 20.1PCh. 20 - Distinguish between the terms spontaneous and...Ch. 20 - State the first law of thermodynamics in terms of...Ch. 20 - State qualitatively the relationship between...Ch. 20 - Why is ΔSvap of a substance always larger than...Ch. 20 - Prob. 20.6PCh. 20 - Prob. 20.7PCh. 20 - Which of these processes are spontaneous? (a)...Ch. 20 - Prob. 20.9PCh. 20 - Which of these processes are spontaneous? (a)...Ch. 20 - Prob. 20.11PCh. 20 - Prob. 20.12PCh. 20 - Prob. 20.13PCh. 20 - Prob. 20.14PCh. 20 - Prob. 20.15PCh. 20 - Prob. 20.16PCh. 20 - Prob. 20.17PCh. 20 - Prob. 20.18PCh. 20 - Prob. 20.19PCh. 20 - Prob. 20.20PCh. 20 - Prob. 20.21PCh. 20 - Prob. 20.22PCh. 20 - Prob. 20.23PCh. 20 - Prob. 20.24PCh. 20 - Predict which substance has greater molar entropy....Ch. 20 - Without consulting Appendix B, arrange each group...Ch. 20 - Without consulting Appendix B, arrange each group...Ch. 20 - Without consulting Appendix B, arrange each group...Ch. 20 - Without consulting Appendix B, arrange each group...Ch. 20 - In the reaction depicted in the molecular scenes,...Ch. 20 - Describe the equilibrium condition in terms of the...Ch. 20 - Prob. 20.32PCh. 20 - For each reaction, predict the sign and find the...Ch. 20 - For each reaction, predict the sign and find the...Ch. 20 - Find for the combustion of ethane (C2H6) to...Ch. 20 - Find for the combustion of methane to carbon...Ch. 20 - Find for the reaction of nitrogen monoxide with...Ch. 20 - Find for the combustion of ammonia to nitrogen...Ch. 20 - Find for the formation of Cu2O(s) from its...Ch. 20 - Find for the formation of HI(g) from its...Ch. 20 - Find for the formation of CH3OH(l) from its...Ch. 20 - Find for the formation of N2O(g) from its...Ch. 20 - Sulfur dioxide is released in the combustion of...Ch. 20 - Oxyacetylene welding is used to repair metal...Ch. 20 - What is the advantage of calculating free energy...Ch. 20 - Given that ΔGsys = −TΔSuniv, explain how the sign...Ch. 20 - Is an endothermic reaction more likely to be...Ch. 20 - Explain your answers to each of the following for...Ch. 20 - With its components in their standard states, a...Ch. 20 - How can ΔS° for a reaction be relatively...Ch. 20 - Calculate ΔG° for each reaction using ...Ch. 20 - Calculate ΔG° for each reaction using ...Ch. 20 - Prob. 20.53PCh. 20 - Prob. 20.54PCh. 20 - Consider the oxidation of carbon...Ch. 20 - Consider the combustion of butane gas: Predict...Ch. 20 - For the gaseous reaction of xenon and fluorine to...Ch. 20 - For the gaseous reaction of carbon monoxide and...Ch. 20 - One reaction used to produce small quantities of...Ch. 20 - A reaction that occurs in the internal combustion...Ch. 20 - As a fuel, H2(g) produces only nonpolluting H2O(g)...Ch. 20 - The U.S. government requires automobile fuels to...Ch. 20 - If K << 1 for a reaction, what do you know about...Ch. 20 - How is the free energy change of a process related...Ch. 20 - The scenes and the graph relate to the reaction of...Ch. 20 - What is the difference between ΔG° and ΔG? Under...Ch. 20 - Calculate K at 298 K for each reaction: MgCO3(s) ⇌...Ch. 20 - Calculate ΔG° at 298 K for each reaction: 2H2S(g)...Ch. 20 - Calculate K at 298 K for each reaction: HCN(aq) +...Ch. 20 - Calculate ΔG° at 298 K for each reaction: 2NO(g) +...Ch. 20 - Use ΔH° and ΔS° values for the following process...Ch. 20 - Use ΔH° and ΔS° values to find the temperature at...Ch. 20 - Prob. 20.73PCh. 20 - Use Appendix B to determine the Ksp of CaF2. Ch. 20 - For the reaction I2(g) + Cl2(g) ⇌ 2ICl(g),...Ch. 20 - For the reaction CaCO3(s) ⇌ CaO(s) + CO2(g),...Ch. 20 - The Ksp of PbCl2 is 1.7×10−5 at 25°C. What is ΔG°?...Ch. 20 - Prob. 20.78PCh. 20 - The equilibrium constant for the...Ch. 20 - The formation constant for the reaction Ni2+(aq) +...Ch. 20 - Prob. 20.81PCh. 20 - Prob. 20.82PCh. 20 - High levels of ozone (O3) cause rubber to...Ch. 20 - A BaSO4 slurry is ingested before the...Ch. 20 - According to advertisements, “a diamond is...Ch. 20 - Prob. 20.86PCh. 20 - Prob. 20.87PCh. 20 - Prob. 20.88PCh. 20 - Is each statement true or false? If false, correct...Ch. 20 - Prob. 20.90PCh. 20 - Prob. 20.91PCh. 20 - Prob. 20.92PCh. 20 - Prob. 20.93PCh. 20 - Write a balanced equation for the gaseous...Ch. 20 - Prob. 20.95PCh. 20 - Hydrogenation is the addition of H2 to double (or...Ch. 20 - Prob. 20.97PCh. 20 - Prob. 20.98PCh. 20 - Prob. 20.99PCh. 20 - Prob. 20.100PCh. 20 - From the following reaction and data, find (a) S°...Ch. 20 - Prob. 20.102PCh. 20 - Prob. 20.103PCh. 20 - Prob. 20.104PCh. 20 - Prob. 20.105PCh. 20 - Prob. 20.106PCh. 20 - Prob. 20.107PCh. 20 - Consider the formation of ammonia: N2(g) + 3H2(g)...Ch. 20 - Kyanite, sillimanite, and andalusite all have the...Ch. 20 - Prob. 20.110PCh. 20 - Prob. 20.111P
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