Skip to main content
Ch.19 - Free Energy & Thermodynamics
Tro - Chemistry: A Molecular Approach 6th Edition
Tro6th EditionChemistry: A Molecular ApproachISBN: 9780137832217Non è quello che usi tu?Cambia libro di testo
Tutti i libri di testoTro 6th EditionCh.19 - Free Energy & ThermodynamicsProblema 73c
Capitolo 19, Problema 73c

Consider the sublimation of iodine at 25.0 °C : I2(s) → I2(g) c. Explain why iodine spontaneously sublimes in open air at 25.0 °C

Guida verificata passo dopo passo
1
1. Sublimation is the process by which a substance changes from a solid to a gas without passing through the liquid phase. For iodine, this process can occur at room temperature (25.0 °C).
2. The spontaneity of a process is determined by the change in Gibbs free energy (ΔG). If ΔG is negative, the process is spontaneous. The Gibbs free energy is given by the equation ΔG = ΔH - TΔS, where ΔH is the change in enthalpy, T is the temperature in Kelvin, and ΔS is the change in entropy.
3. In the case of iodine sublimation, the process is endothermic (ΔH > 0) because energy is absorbed to break the intermolecular forces holding the iodine molecules together in the solid phase. However, the process leads to a significant increase in entropy (ΔS > 0) because gas particles are much more disordered than solid particles.
4. At room temperature, the TΔS term in the Gibbs free energy equation is large enough to make ΔG negative, despite the positive ΔH. This is because the increase in disorder (entropy) is a dominant factor at this temperature.
5. Therefore, iodine spontaneously sublimes in open air at 25.0 °C because the process results in a decrease in Gibbs free energy, primarily due to the significant increase in entropy when iodine changes from a solid to a gas.

Risposta video verificata per un problema simile:

Questa soluzione video è stata consigliata dai nostri tutor come utile per risolvere questo problema.
Durata del video:
1m

Concetti chiave

Ecco i concetti essenziali che devi comprendere per rispondere correttamente alla domanda.

Sublimation

Sublimation is the phase transition in which a substance changes directly from a solid to a gas without passing through the liquid phase. This process occurs when the molecules in the solid gain enough energy to overcome intermolecular forces and escape into the gas phase. For iodine, sublimation is favored at certain temperatures and pressures, particularly when the solid is exposed to open air.
Video consigliato:
Percorso guidato
01:52
Sublimation Phase Change Example

Vapor Pressure

Vapor pressure is the pressure exerted by a vapor in equilibrium with its solid or liquid phase at a given temperature. For iodine, at 25.0 °C, the vapor pressure is significant enough to allow iodine molecules to escape from the solid phase into the gas phase. When the vapor pressure exceeds the atmospheric pressure, sublimation occurs spontaneously, leading to the transition of solid iodine to gaseous iodine.
Video consigliato:
Percorso guidato
02:40
Raoult's Law and Vapor Pressure

Thermodynamics and Spontaneity

Thermodynamics helps determine whether a process is spontaneous based on changes in enthalpy and entropy. For iodine subliming at 25.0 °C, the process is driven by an increase in entropy, as gas molecules have greater disorder than solid molecules. The Gibbs free energy change (ΔG) for sublimation is negative under these conditions, indicating that the process occurs spontaneously in open air.
Video consigliato:
Percorso guidato
04:20
Spontaneity of Processes
Pratica correlata
Domanda del libro di testo

Consider the evaporation of methanol at 25.0 °C : CH3OH(l) → CH3OH(g) b. Find ΔGr at 25.0 °C under the following nonstandard conditions: i. PCH3OH = 150.0 mmHg ii. PCH3OH = 100.0 mmHg iii. PCH3OH = 10.0 mmHg

2431
views
Domanda del libro di testo

Consider the evaporation of methanol at 25.0 °C : CH3OH(l) → CH3OH(g) a. Find ΔG°r at 25.0 °C.

2543
views
Domanda del libro di testo

Consider the evaporation of methanol at 25.0 °C : CH3OH(l) → CH3OH(g) c. Explain why methanol spontaneously evaporates in open air at 25.0 °C

617
views
Domanda del libro di testo

Consider the sublimation of iodine at 25.0 °C : I2(s) → I2(g) b. Find ΔG°rxn at 25.0 °C under the following nonstandard conditions: i. PI2 = 1.00 mmHg ii. PI2 = 0.100 mmHg

2930
views
2
rank
Domanda del libro di testo

Determine ΔG° for the reaction: Fe2O3(s) + 3 CO(g) → 2 Fe(s) + 3 CO2(g) Use the following reactions with known ΔG°rxn values:

2 Fe(s) + 3/2 O2(g) → Fe2O3(s) ΔG°rxn = -742.2 kJ

CO(g) + 12 O2( g) → CO2(g) ΔG°rxn = -257.2 kJ

3009
views
2
rank