O:H-O Bond Anomalous Relaxation Resolving Mpemba Paradox (1310.6514v2)

Abstract: We demonstrate that the Mpemba paradox arises intrinsically from the release rate of energy initially stored in the covalent H-O part of the O:H-O bond in water albeit experimental conditions. Generally, heating raises the energy of a substance by lengthening and softening all bonds involved. However, the O:H nonbond in water follows actively the general rule of thermal expansion and drives the H-O covalent bond to relax oppositely in length and energy because of the inter-electron-electron pair coupling [J Phys Chem Lett 4, 2565 (2013); ibid 4, 3238 (2013)]. Heating stores energy into the H-O bond by shortening and stiffening it. Cooling the water as the source in a refrigerator as a drain, the H-O bond releases its energy at a rate that depends exponentially on the initially storage of energy, and therefore, Mpemba effect happens. This effect is formulated in terms of the relaxation time tau to represent all possible processes of energy loss. Consistency between predictions and measurements revealed that the tau drops exponentially intrinsically with the initial temperature of the water being cooled.

• The paper demonstrates that the Mpemba paradox arises from an exponential decrease in relaxation time of the H-O bond at higher initial temperatures.
• The paper employs an exponential decay model to quantify rapid energy release from the O:H-O bond during the cooling of hot water.
• The paper implies that understanding water’s bond dynamics can refine phase transition models, impacting fields like cryopreservation and climate science.

Overview of "O:H-O Bond Anomalous Relaxation Resolving Mpemba Paradox"

The paper, "O:H-O Bond Anomalous Relaxation Resolving Mpemba Paradox," addresses one of the longstanding conundrums in thermodynamics, the Mpemba paradox, which suggests that warmer water may freeze faster than cooler water. The authors attribute the Mpemba effect to the peculiar relaxation behavior of the O:H-O bond in water, highlighting its energy dynamics and structural changes under thermal stimuli.

Mechanism of the Mpemba Effect

The intrinsic mechanism behind the Mpemba effect in this work is rooted in the energy dynamics of the asymmetric O:H-O bond in water. The paper elucidates that the release of energy, crucial for the Mpemba effect, originates from the H-O bond, whose relaxation dynamics depend on the bond’s initial energy state. Contrary to common materials where heating causes bond lengthening, the O:H-O bond in water experiences bond stiffening upon heating due to electron pair repulsion. This results in the H-O bond storing potential energy that can be more readily released upon cooling.

Relaxation Time Correlation

The authors introduce the concept of relaxation time, denoted as τ, to characterize the rate of energy release from the H-O bond during cooling. The work demonstrates that τ decreases exponentially with higher initial water temperatures, indicating that the energy release rate is significantly faster for hot water compared to cold. This relation is validated through the formulation of an exponential decay model that accurately predicts empirical observations.

Anomalies in O:H-O Bond Behavior

The paper details the unique behavior of the hydrogen bond under thermal influences and how this behavior underpins the Mpemba effect. The short and strong H-O covalent bond, in contrast to the weak O:H van der Waals bond, dynamically alters its energy state and relaxation pathways depending on the initial thermal conditions. These findings suggest that water's unique molecular structure and bonding characteristics are critical to observing this paradox.

Implications and Future Prospects

This research carries substantial implications for understanding aqueous phase transitions and the local structural dynamics of water. It broadens the perspective on energy relaxation in molecular systems beyond classical explanations such as evaporation or convection. The clarification of the Mpemba effect at the molecular level opens avenues for developing more precise models of phase transitions, potentially influencing fields such as cryopreservation and climate modeling.

Future studies could benefit from exploring the inverse phenomenon—whether colder water boils faster—drawing parallels with the current findings. Moreover, extending this analysis to other anomalous materials could yield insights into materials science and condensed matter physics.

Conclusion

Through this detailed examination of the O:H-O bond relaxation in water, the authors provide a substantive explanation for the Mpemba effect. The insights gained enhance the comprehension of hydrogen bonding under non-equilibrium conditions, marking a meaningful contribution to the field of thermodynamics. While the findings are specific to water, they offer a template for exploring similar anomalies in other substances, inviting future research into broader thermodynamic phenomena.