Textbook Question
A local weather station reports the barometric pressure as 29.5 inHg (inches of Hg). Convert this pressure to torr and to atm.
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Ch.8 Gases, Liquids and Solids
McMurry8th EditionFundamentals of General, Organic, and Biological ChemistryISBN: 9780134015187
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Table of contents
- Ch.1 Matter and Measurements27
- Ch.2 Atoms and the Periodic Table20
- Ch.3 Ionic Compounds8
- Ch.4 Molecular Compounds23
- Ch.5 Classification & Balancing of Chemical Reactions12
- Ch.6 Chemical Reactions: Mole and Mass Relationships28
- Ch.7 Chemical Reactions: Energy, Rate and Equilibrium64
- Ch.8 Gases, Liquids and Solids24
- Ch.9 Solutions52
- Ch.10 Acids and Bases25
- Ch.11 Nuclear Chemistry22
- Ch.12 Introduction to Organic Chemistry: Alkanes57
- Ch.13 Alkenes, Alkynes, and Aromatic Compounds47
- Ch.14 Some Compounds with Oxygen, Sulfur, or a Halogen50
- Ch.15 Aldehydes and Ketones45
- Ch.16 Amines42
- Ch.17 Carboxylic Acids and Their Derivatives57
- Ch.18 Amino Acids and Proteins82
- Ch.19 Enzymes and Vitamins63
- Ch.20 Carbohydrates44
- Ch.21 The Generation of Biochemical Energy65
- Ch.22 Carbohydrate Metabolism45
- Ch.23 Lipids42
- Ch.24 Lipid Metabolism33
- Ch.25 Protein and Amino Acid Metabolism24
- Ch.26 Nucleic Acids and Protein Synthesis45
McMurry8th EditionFundamentals of General, Organic, and Biological ChemistryISBN: 9780134015187Not the one you use?Change textbook
Chapter 8, Problem 1b
The change of state from liquid H2O to gaseous H2O has ∆H = +9.72 kcal/mol(+40.7 kJ/mol) and ∆S = -26.1 cal/(mol • K) [-109 J/(mol •K)].
b. What are the values of ∆H and ∆S (in kcal/mol and kJ/mol) for the change from gaseous to liquid H2O?
Verified step by step guidance1
Step 1: Understand the problem. The given values of ∆H and ∆S are for the phase change from liquid H2O to gaseous H2O. To find the values for the reverse process (gaseous to liquid H2O), we need to reverse the signs of both ∆H and ∆S because the direction of the process is reversed.
Step 2: Reverse the sign of ∆H. The given ∆H for liquid to gas is +9.72 kcal/mol (or +40.7 kJ/mol). For the reverse process (gas to liquid), ∆H will be -9.72 kcal/mol (or -40.7 kJ/mol).
Step 3: Reverse the sign of ∆S. The given ∆S for liquid to gas is -26.1 cal/(mol • K) (or -109 J/(mol • K)). For the reverse process (gas to liquid), ∆S will be +26.1 cal/(mol • K) (or +109 J/(mol • K)).
Step 4: Ensure unit consistency. The values for ∆H and ∆S are already provided in both kcal/mol and kJ/mol, so no further unit conversion is necessary.
Step 5: Summarize the results. For the change from gaseous to liquid H2O, ∆H = -9.72 kcal/mol (-40.7 kJ/mol) and ∆S = +26.1 cal/(mol • K) [+109 J/(mol • K)].
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Enthalpy Change (∆H)
Enthalpy change (∆H) refers to the heat content change of a system during a process at constant pressure. In the context of phase changes, a positive ∆H indicates that heat is absorbed when a substance transitions from a liquid to a gas, while a negative ∆H indicates heat is released during the reverse process. For the transition from gas to liquid, ∆H will be the negative of the value given for the liquid to gas transition.
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Entropy Change (∆S)
Entropy change (∆S) measures the degree of disorder or randomness in a system. A negative ∆S value, as seen in the transition from liquid to gas, indicates a decrease in disorder when moving from a gaseous state to a liquid state. Thus, for the reverse transition from gas to liquid, ∆S will be the negative of the value provided for the liquid to gas transition, reflecting the increase in order.
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Thermodynamic Relationships
Thermodynamic relationships, particularly the principles of reversibility, dictate that the values of ∆H and ∆S for a process are equal in magnitude but opposite in sign when the process is reversed. This means that to find the values for the transition from gaseous to liquid H2O, one simply takes the negative of the given values for the liquid to gas transition, allowing for straightforward calculations in thermodynamic problems.
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Related Practice
Textbook Question
Determine the percent composition of air in the lungs from the following composition in partial pressures: PN2= 573 mmHg, PO2 = 100 mmHg, PCO2 = 40 mmHg, and PH2O = 47 mmHg; all at 37 °C and 1 atm pressure.
Textbook Question
The change of state from liquid H2O to gaseous H2O has ∆H = +9.72 kcal/mol(+40.7 kJ/mol) and ∆S = -26.1 cal/(mol • K) [-109 J/(mol •K)].
a. Is the change from liquid to gaseous H2O favored or unfavored by ∆H? By ∆S?
Textbook Question
Would you expect the boiling points to increase or decrease in the following series? Explain.
a. Kr, Ar, Ne