在酸中无水和水辅助的质子流动性
Michael J Janik1, Robert J Davis, Matthew Neurock
1Department of Chemical Engineering, University of Virginia, Charlottesville, Virginia 22904-4741, USA.
Journal of the American Chemical Society
|April 7, 2005
概括
酸中的质子迁移受到水的显著影响. 即使是少量的水也会大大降低质子跳跃的能量屏障,提高运动速度.
科学领域:
- 材料科学 材料科学 材料科学
- 物理化学 物理化学
- 计算化学的计算化学
背景情况:
- 酸是催化和能量储存中的关键材料.
- 了解质子迁移对于优化其性能至关重要.
- 固体酸中的质子流动性通常受到高激活障碍的限制.
研究的目的:
- 调查酸中质子迁移的能量和动力学.
- 阐明水在促进质子运输中的作用.
- 为了确定质子跳跃的激活能量和速率常数.
主要方法:
- 非局部梯度校正密度函数理论 (DFT) 的计算.
- 量子道效应的半古典过渡状态理论.
- 分析Keggin单元上的质子跳跃路径.
主要成果:
- 计算的无水质子跳跃激活能量为103.3kJ/mol.
- 量子道显著影响了350K以下的质子流动性.
- 水吸附显著降低了激活屏障,达到11.2kJ/mol.
- 质子转移在水的存在下通过结合来促进.
结论:
- 水在 phosphotungstic 酸中增强质子导电性方面发挥着关键作用.
- 质子迁移的激活能量对水的部分压力高度敏感.
- 计算方法为复杂材料中的质子动力学提供了宝贵的见解.
相关概念视频
Water: A Bronsted-Lowry Acid and Base
The reaction between a Brønsted-Lowry acid and water is called acid ionization. For example, when hydrogen fluoride dissolves in water and ionizes, protons are transferred from hydrogen fluoride molecules to water molecules, yielding hydronium ions and fluoride ions:
Weak Acid Solutions
Few compounds act as strong acids. A far greater number of compounds behave as weak acids and only partially react with water, leaving a large majority of dissolved molecules in their original form and generating a relatively small amount of hydronium ions. Weak acids are commonly encountered in nature, being the substances partly responsible for the tangy taste of citrus fruits, the stinging sensation of insect bites, and the unpleasant smells associated with body odor. A familiar example of a...
Acid Strength and Molecular Structure
Binary Acids and Bases
In the absence of any leveling effect, the acid strength of binary compounds of hydrogen with nonmetals (A) increases as the H-A bond strength decreases down a group in the periodic table. For group 17, the order of increasing acidity is HF < HCl < HBr < HI. Likewise, for group 16, the order of increasing acid strength is H2O < H2S < H2Se < H2Te. Across a row in the periodic table, the acid strength of binary hydrogen compounds increases with increasing...
In the absence of any leveling effect, the acid strength of binary compounds of hydrogen with nonmetals (A) increases as the H-A bond strength decreases down a group in the periodic table. For group 17, the order of increasing acidity is HF < HCl < HBr < HI. Likewise, for group 16, the order of increasing acid strength is H2O < H2S < H2Se < H2Te. Across a row in the periodic table, the acid strength of binary hydrogen compounds increases with increasing...
pH
The potential of hydrogen (pH) is a measure of the acidity or basicity of a water-based solution determined by the concentration of hydronium ions (H3O+). In one liter of pure water at neutral pH, there are 1×10−7 moles of hydronium ions. However, the extensive range of hydronium ion concentrations present in water-based solutions makes measuring pH in moles cumbersome. Therefore, a pH scale was developed to convert moles of hydronium ions into the negative logarithm of the hydronium ion...
Solubility
Solution, Solubility, and Solubility Equilibrium
A solution is a homogeneous mixture composed of a solvent, the major component, and a solute, the minor component. The physical state of a solution—solid, liquid, or gas—is typically the same as that of the solvent. Solute concentrations are often described with qualitative terms such as dilute (of relatively low concentration) and concentrated (of relatively high concentration).
In a solution, the solute particles (molecules, atoms, and/or ions)...
A solution is a homogeneous mixture composed of a solvent, the major component, and a solute, the minor component. The physical state of a solution—solid, liquid, or gas—is typically the same as that of the solvent. Solute concentrations are often described with qualitative terms such as dilute (of relatively low concentration) and concentrated (of relatively high concentration).
In a solution, the solute particles (molecules, atoms, and/or ions)...
Titration in Nonaqueous Solvents
Most acid-base titrations are performed in an aqueous medium. In aqueous titrations, water competes with weaker acids or bases for proton donation or acceptance, leading to ambiguous endpoints in the titration curve. Water also affects the partial ionization of weak acids or bases. For example, water accepts a proton from acetic acid to form hydronium and acetate ions. The hydronium ion formed is a stronger acid than acetic acid, and the acetate ion is a stronger base than water. As a result,...


