Textbook Question
Without referring to tables, predict which of the following has the higher enthalpy in each case: (a) 1 mol I2(s) or 1 mol I2(g) at the same temperature
Ch.5 - Thermochemistry
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232
Not the one you use?Change textbookSelect a different textbook
Table of contents
- Ch.1 - Introduction: Matter, Energy, and Measurement177
- Ch.2 - Atoms, Molecules, and Ions231
- Ch.3 - Chemical Reactions and Reaction Stoichiometry216
- Ch.4 - Reactions in Aqueous Solution189
- Ch.5 - Thermochemistry175
- Ch.6 - Electronic Structure of Atoms168
- Ch.7 - Periodic Properties of the Elements150
- Ch.8 - Basic Concepts of Chemical Bonding177
- Ch.9 - Molecular Geometry and Bonding Theories200
- Ch.10 - Gases179
- Ch.11 - Liquids and Intermolecular Forces113
- Ch.12 - Solids and Modern Materials154
- Ch.13 - Properties of Solutions157
- Ch.14 - Chemical Kinetics199
- Ch.15 - Chemical Equilibrium128
- Ch.16 - Acid-Base Equilibria164
- Ch.17 - Additional Aspects of Aqueous Equilibria163
- Ch.18 - Chemistry of the Environment105
- Ch.19 - Chemical Thermodynamics164
- Ch.20 - Electrochemistry171
- Ch.21 - Nuclear Chemistry122
- Ch.22 - Chemistry of the Nonmetals82
- Ch.23 - Transition Metals and Coordination Chemistry79
- Ch.24 - The Chemistry of Life: Organic and Biological Chemistry16
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Not the one you use?Change textbook
Chapter 5, Problem 42b
Without referring to tables, predict which of the following has the higher enthalpy in each case: (b) 2 mol of iodine atoms or 1 mol of I2
Verified step by step guidance1
Understand the concept of enthalpy, which is a measure of the total energy of a thermodynamic system, usually expressed in joules or kilojoules per mole.
Recognize that the enthalpy of a substance depends on its molecular structure and the bonds between atoms. Stronger bonds generally mean lower enthalpy.
Consider the molecular structure of iodine in its different forms: as individual iodine atoms and as I2 molecules. I2 consists of two iodine atoms bonded together.
Recall that forming a bond releases energy, thus stabilizing the system. Therefore, a molecule of I2, which has a covalent bond between two iodine atoms, would have a lower enthalpy compared to separate iodine atoms which have no bonds.
Conclude that 1 mol of I2 would generally have a lower enthalpy than 2 mol of iodine atoms, because the bonded I2 molecules are in a lower energy state compared to separate atoms.
Verified video answer for a similar problem:
This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
1mWas this helpful?
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Enthalpy
Enthalpy is a thermodynamic quantity that represents the total heat content of a system. It is defined as the internal energy of the system plus the product of its pressure and volume. Enthalpy changes are crucial in chemical reactions, as they indicate whether a reaction is exothermic (releases heat) or endothermic (absorbs heat). Understanding enthalpy helps predict the stability and reactivity of substances.
Recommended video:
Guided course
02:34
Enthalpy of Formation
Diatomic Molecules
Diatomic molecules consist of two atoms, which can be of the same or different elements. In the case of iodine, I2 is a diatomic molecule made up of two iodine atoms bonded together. The formation of a diatomic molecule from individual atoms typically involves a release of energy, resulting in a lower enthalpy for the molecule compared to its constituent atoms. This concept is essential for comparing the enthalpy of I2 and free iodine atoms.
Recommended video:
Guided course
03:10Homonuclear Diatomic Molecules
Bond Energy
Bond energy is the amount of energy required to break a bond between two atoms in a molecule. In the context of I2, the bond energy reflects the stability of the I-I bond. When comparing 2 mol of iodine atoms to 1 mol of I2, the bond energy indicates that breaking the I-I bond in I2 requires energy, thus making I2 lower in enthalpy than the separate iodine atoms. This concept is key to understanding the energy changes involved in molecular formation.
Recommended video:
Guided course
01:50Bond Energy
Related Practice
Textbook Question
Without referring to tables, predict which of the following has the higher enthalpy in each case: (c) 1 mol I2(g) and 1 mol H2(g) at 25 °C or 2 mol HI(g) at 25 °C (d) 1 mol H2(g) at 100 °C or 1 mol H2(g) at 300 °C.
1
views
Textbook Question
Consider the following reaction: 2 CH3OH(g) → 2 CH4(g) + O2(g) ΔH = +252.8 kJ (b) Calculate the amount of heat transferred when 24.0 g of CH3OH(g) is decomposed by this reaction at constant pressure.
Textbook Question
Atomic hydrogen (H) is used in welding (AHW). The atoms recombine to hydrogen molecules with a large release of heat according to the following reaction: 2 H(g) → H2(g) (b) Which has the higher enthalpy under these conditions, 2 H(g) or H2(g)?
Textbook Question
Atomic hydrogen (H) is used in welding (AHW). The atoms recombine to hydrogen molecules with a large release of heat according to the following reaction: 2 H(g) → H2(g) (a) Using the thermodynamic data in Appendix C, calculate the enthalpy change for this reaction per mole of H2.