Given the general properties of water and ammonia, comment...

Given the general properties of water and ammonia, comment on the problems that a biological system (as we know it) would have developing in an ammonia medium. $$\begin{array}{lll} \text { Boiling point } & \mathrm{H}_{2} \mathrm{O} & \mathrm{NH}_{3} \\ \text { Melting point } & 373.15 \mathrm{K} & 239.65 \mathrm{K} \\ \text { Molar heat capacity } & 273.15 \mathrm{K} & 195.3 \mathrm{K} \\ \text { Molar heat of vaporization } & 45.3 \mathrm{J} / \mathrm{K} \cdot \mathrm{mol} & 8.53 \mathrm{J} / \mathrm{K} \cdot \mathrm{mol} \\ \text { Molar heat of fusion } & 40.79 \mathrm{kJ} / \mathrm{mol} & 23.3 \mathrm{kJ} / \mathrm{mol} \\\text { Viscosity } & 0.001 \mathrm{N} \cdot \mathrm{s} / \mathrm{m}^{2} & 0.0254 \mathrm{N} \cdot \mathrm{s} / \mathrm{m}^{2} \\ & & (\text { at } 240 \mathrm{K}) \\ \text { Dipole moment } & 1.82 \mathrm{D} & 1.46 \mathrm{D} \\ \text { Phase at } 300 \mathrm{K} & \text { Liquid } & \text { Gas } \end{array}$$

Given the general properties of water and ammonia, comment on the problems that a biological system (as we know it) would have developing in an ammonia medium.
$$\begin{array}{lll}
\text { Boiling point } & \mathrm{H}_{2} \mathrm{O} & \mathrm{NH}_{3} \\
\text { Melting point } & 373.15 \mathrm{K} & 239.65 \mathrm{K} \\
\text { Molar heat capacity } & 273.15 \mathrm{K} & 195.3 \mathrm{K} \\
\text { Molar heat of vaporization } & 45.3 \mathrm{J} / \mathrm{K} \cdot \mathrm{mol} & 8.53 \mathrm{J} / \mathrm{K} \cdot \mathrm{mol} \\
\text { Molar heat of fusion } & 40.79 \mathrm{kJ} / \mathrm{mol} & 23.3 \mathrm{kJ} / \mathrm{mol} \\\text { Viscosity } & 0.001 \mathrm{N} \cdot \mathrm{s} / \mathrm{m}^{2} & 0.0254 \mathrm{N} \cdot \mathrm{s} / \mathrm{m}^{2} \\
& & (\text { at } 240 \mathrm{K}) \\
\text { Dipole moment } & 1.82 \mathrm{D} & 1.46 \mathrm{D} \\
\text { Phase at } 300 \mathrm{K} & \text { Liquid } & \text { Gas }
\end{array}$$

Key Concepts

Solvent Properties

This concept pertains to the ability of a liquid to dissolve various substances, which is essential for supporting biochemical reactions. The polarity, dielectric constant, and hydrogen bonding capabilities of a solvent directly affect how biomolecules interact, fold, and react. Understanding solvent properties is key when comparing water with other potential solvents like ammonia.

Thermal Properties

Thermal characteristics such as boiling point, melting point, specific heat capacity, and the heats of fusion and vaporization determine the temperature range over which a solvent remains liquid and stable. For biological systems, a solvent must be liquid under ambient conditions to support reaction dynamics and homeostasis, making these properties critical in evaluating alternative solvents like ammonia.

Phase Behavior

The phase behavior of a substance under given temperature and pressure conditions is vital for biological viability. Life as we know it relies on a liquid medium, and a solvent that is gaseous at standard temperatures (like ammonia at 300 K) would not support the same biological processes. Understanding phase transitions helps in assessing the suitability of any liquid media for sustaining life.

Viscosity

Viscosity influences molecular diffusion and the rates of biochemical reactions. A solvent with high viscosity can slow down the movement and interaction of molecules, which may hinder efficient metabolic processes. The differences in viscosity between water and alternative solvents have significant implications for the dynamics of cellular activities.

Hydrogen Bonding and Dipole Moments

These molecular characteristics are crucial for the stabilization of macromolecular structures and for mediating interactions between molecules through weak bonds. Variations in hydrogen bonding strength and dipole moments affect solvation, reactivity, and the structural integrity of biomolecules, which are all critical to the functioning of biological systems.

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