Chapter 8: Problem 88
Match each of the following energy changes with one of the processes given: ionization energy, electron affinity, bond enthalpy, and standard enthalpy of formation. (a) \(\mathrm{F}(g)+e^{-} \longrightarrow \mathrm{F}^{-}(g)\) (b) \(\mathrm{F}_{2}(g) \longrightarrow 2 \mathrm{~F}(g)\) (c) \(\mathrm{Na}(g) \longrightarrow \mathrm{Na}^{+}(g)+e^{-}\) (d) \(\mathrm{Na}(s)+\frac{1}{2} \mathrm{~F}_{2}(g) \longrightarrow \mathrm{NaF}(s)\)
Short Answer
Step by step solution
Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Ionization Energy
For instance, in process (c), \( \mathrm{Na}(g) \rightarrow \mathrm{Na}^{+}(g)+e^{-} \), the energy required to remove an electron from sodium in its gaseous state represents the ionization energy. Several factors influence ionization energy, including:
- Atomic size: Larger atoms generally have lower ionization energy because the outer electrons are further from the nucleus and less tightly held.
- Nuclear charge: A higher positive charge in the nucleus increases ionization energy, making it more difficult to remove an electron.
- Electron shielding: Inner electrons can shield outer electrons from the nucleus's pull, affecting the ionization energy.
Electron Affinity
In the context of process (a), when fluorine accepts an electron to become \( \mathrm{F}^{-}(g) \), energy is released or absorbed. This concept is crucial for understanding how atoms gain electrons and how they might interact with other elements.
- Sign: Unlike ionization energy, which is always positive, electron affinity can be either negative or positive based on whether energy is released (exothermic) or absorbed (endothermic).
- Factors: Exceptional cases, like elements with full electron shells, may have different electron affinities due to stability concerns.
Bond Enthalpy
Higher bond enthalpy values indicate stronger bonds.Key points about bond enthalpy include:
- Average Values: Bond enthalpies are often averaged over similar compounds because the bond energy can change based on the molecular environment.
- Predicting Reaction Heat: Sum of bond enthalpies of reactants and products helps predict whether a reaction is exothermic or endothermic.
Standard Enthalpy of Formation
Taking process (d) as an example,\( \mathrm{Na}(s)+\frac{1}{2} \mathrm{~F}_{2}(g) \rightarrow \mathrm{NaF}(s) \), we observe the specific energy changes involved in forming sodium fluoride from sodium and fluorine gas in their most stable forms.Insights into standard enthalpy of formation include:
- Standard Conditions: Measurements taken under specific conditions (usually 298 K and 1 atm) ensure consistency and comparability.
- Significance: Provides a basis for calculating the enthalpy changes of broader chemical reactions using Hess's law.
- Thermodynamic Reference: Often used as a reference to calculate other reaction enthalpies.