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Recommended experimental surface tension values and a temperature-dependent interpolating formula for liquid water in equilibrium with its vapour. Printed page 3 gives the formula and validity range; Table 1 starts on printed page 4.

Official release: iapws.org/technical-guidance/release/Surf-H2O

PDF: iapws.org/documents/release/Surf-H2O.download

Ribose is a monosaccharide with molecular formula ${\mathrm{C}}_5{\mathrm{H}}_{10}{\mathrm{O}}_5$. Its biologically familiar form is D-ribose, an aldopentose whose open-chain Fischer projection has $\mathrm{CHO}$ at the top, ${\mathrm{CH}}_2\mathrm{OH}$ at the bottom, and hydroxy groups on the right at C2, C3, and C4. The opposite horizontal substituents are hydrogen. See McMurry, Organic Chemistry, 25.3: D-ribose and D-glucose configurations.

Read the drawing by counting groups: $\mathrm{CHO}$ contributes $\mathrm{CHO}$, three $\mathrm{CHOH}$ groups contribute ${\mathrm{C}}_3{\mathrm{H}}_6{\mathrm{O}}_3$, and ${\mathrm{CH}}_2\mathrm{OH}$ contributes $\mathrm{C}{\mathrm{H}}_3\mathrm{O}$. Their sum is ${\mathrm{C}}_5{\mathrm{H}}_{10}{\mathrm{O}}_5$. The count checks composition; the right/right/right pattern additionally specifies the stereochemistry of D-ribose.

In RNA, ribose occurs as a ring within each nucleotide, joining a nucleobase to the phosphate-linked backbone. Its C2 position retains a hydroxy group, unlike deoxyribose in DNA. In a nucleotide, the sugar positions carry primes, so this is C2′. See Alberts et al.: nucleotide sugars in RNA and DNA. Free ribose in water is also predominantly cyclic, with several ring forms in chemical equilibrium and very little open-chain form; the Fischer projection is valuable for comparing configurations, not for estimating their abundances. See Mason et al., The Conformation of a Ribose Derivative in Aqueous Solution: A Neutron Scattering and Molecular Dynamics Study (2013), introduction.

A depositional body built where a sediment-bearing river enters a more slowly moving body of water. Its internal structure and basin context distinguish it from other fan-shaped deposits.

Saponification is hydrolysis of an ester under basic conditions. The conductometric saponification assay follows ethyl acetate consumption by hydroxide, producing ethanol and an acetate ion; its equal-starting-concentration case provides a practical second-order reaction example.

Saponification is ester hydrolysis promoted by a chemical base, with net consumption of hydroxide to form a carboxylate and an alcohol. For a carboxylic acid-derived ester, the net chemical equation isThe hydroxide is a reactant, rather than merely a regenerated catalyst.^[ref]

For ethyl acetate, the balanced chemical equation becomesBoth sides contain four carbon chemical atoms, nine hydrogen chemical atoms, three oxygen chemical atoms, and net electric charge $-1$. A sodium ion supplied by sodium hydroxide is a spectator ion; the net ionic equation omits it without losing electric charge conservation.

In the usual reaction mechanism, hydroxide adds to the carbonyl group, making a reaction intermediate. Departure of the alcohol's conjugate base gives a carboxylic acid; transfer of a proton then gives the carboxylate and the alcohol. Subsequent addition of a chemical acid gives the carboxylic acid by protonation:This separate acidification changes the reaction product's protonation state.^[ref]

The conductometric saponification assay makes hydroxide consumption observable. A university procedure equilibrates separate ethyl acetate and sodium hydroxide stocks in constant-temperature baths, then mixes them in a rinsed conductivity cell. Two platinum electrodes and an alternating-voltage Wheatstone bridge supply an electrical resistance readout. A matched sodium hydroxide–water dilution checks the initial signal; potassium chloride calibrates the cell constant. Replacing hydroxide with less mobile acetate ions lowers electrical conductance, supporting an inference about changing concentration. The manual supplies a procedure rather than measured outcomes. Temperature drift or additional ions can change the signal; it cannot alone identify the full reaction mechanism.^[ref]

A triglyceride contains three ester linkages joining glycerol to fatty acid-derived acyl groups. Complete saponification therefore consumes three hydroxide equivalents per triglyceride, yielding one glycerol and three fatty acid carboxylates.^[ref]

Writing the three hydrocarbon groups separately allows their compositions to differ:This is the preceding ester chemical equation applied three times: each linkage supplies one carboxylate, and each formerly esterified oxygen on the glycerol scaffold gains one hydrogen. The two sides retain the same three ${\mathrm{R}}_i$ groups and have net electric charge $-3$.

Soap consists of sodium or potassium salts of long-chain fatty acids. Its carboxylate head is hydrophilic, while its long hydrocarbon tail is hydrophobic. This makes it an amphiphile and a surfactant: the tails can associate with grease while the heads remain exposed to water, helping disperse grease for rinsing. An acetate ion is also a carboxylate, but lacks the long hydrophobic tail that gives soap this cleaning role.^[ref]

A concrete experiment turns the phase coexistence curve into pairs of temperature and saturation pressure. A 1969 paper reports water measurements made in 1942 and 1947–1949 using a boiler and precision mercury manometer. Platinum resistance thermometers read the boiler temperature through a resistance bridge. The pressure-transfer line passed through an ice-water condenser and a dry-ice trap; helium filled connecting sections. Corrected mercury column height gave the pressure at the thermometer coils, including hydrostatic pressure contributions from water vapor, helium, mercury, and mercury vapor.^[ref]

Controls included normal/reversed-lead readings, readings at two thermometer electric currents extrapolated to zero current to remove self-heating, repeated bridge calibration, and daily triple point thermometer calibration checks. Cellar temperature measurements corrected fluid-column and gauge-block thermal expansion. One measurement series was excluded because a trapped gas bubble was suspected of corrupting the mercury head. The paper adjusted measurements to round temperatures using previously tabulated slopes; those adjusted values therefore are not independent measurements of those slopes.^[ref]

The thermodynamic inference requires liquid and gas in phase coexistence, a well-defined common temperature, and a pressure corrected to that same location. Leaks, contamination, or a temperature gradient can spoil that interpretation. A separate calorimetry measurement of latent heat, together with the two specific volumes, allows a test of the full Clapeyron equation. Converting a measured phase coexistence curve slope directly into latent heat instead assumes that equation; it is not an independent test.

The ambient water vapor partial pressure divided by the equilibrium saturation pressure over a stated reference surface at the same temperature. Relative to flat pure water, atmospheric supersaturation is $s=S-1$. A curved solute-containing cloud droplet generally has a different equilibrium saturation ratio from unity.

The elevation of the ocean surface relative to a specified reference. Global mean, local relative and instantaneous levels answer different questions. Changes of basin capacity, water amount and surface topography can alter flooded continental shelf area and the distribution of marine environments.

An authored manufacturer experiment used an Agilent 1260 Infinity Bio-inert Quaternary LC with Bio SEC-3 $300\mathring{\mathrm{A}}$ columns, $7.8\mathrm{mm}$ diameter and $150$ or $300\mathrm{mm}$ length. Four pump channels mixed water, sodium chloride, and two phosphate solutions into $20\mathrm{mmol}{\mathrm{L}}^{-1}$ phosphate at pH $7.0$, varying salt from $0.2$ to $0.6\mathrm{mol}{\mathrm{L}}^{-1}$. At $1.0\mathrm{mL}\mathrm{mi}{\mathrm{n}}^{-1}$ and $30{}^{\circ }\mathrm{C}$, the readouts were diode-array absorbance, differential refractive index, and scattering at $15^{\circ }$ and $90^{\circ }$. A supplied protein standard mixture calibrated retention; bovine serum albumin calibrated scattering constants and inter-detector delay. Increasing salt improved separation of two α-chymotrypsinogen A peaks; two $300\mathrm{mm}$ columns also resolved peaks that one column did not. At $0.5\mathrm{mol}{\mathrm{L}}^{-1}$ salt, the two scattering-derived estimates were about $26,100$ and $25,800\mathrm{g}\mathrm{mo}{\mathrm{l}}^{-1}$. The author inferred a possible size-changing conformation difference, rather than doubling of molar mass. The same poster shows delayed, tailing lysozyme peaks from unwanted interactions.^[ref]

The salt comparison and the independent mass readout constrain interpretation, but do not uniquely prove a particular protein structure. Salt can change protein folding, protein aggregation, and packing interactions together. In ideal SEC there is no adsorption; attraction from the hydrophobic effect or forces described by electrostatics can cause additional retention, tailing, and loss of recovered sample. Repulsion can instead reduce pore entry. A peak beyond $V_t$ contradicts the simple nonbinding model, rather than extending its size calibration.

Useful proposed controls compare a solvent blank, fresh calibration standards bracketing the sample, several injection amounts and volumes, and recovered sample quantity with injected quantity using an appropriately calibrated detector. Keep temperature and volumetric flow rate fixed while testing pH or ionic strength. Compare an independent mass readout before declaring an early peak an aggregate. Loss of an insoluble species during filtration, on-column association or dissociation, overloading, and broad unresolved peaks can all hide the original sample population. These are interpretation checks and limitations, not measurements invented for the figures.

A living seed's restriction on germination under otherwise favorable conditions, distinct from insufficient water, unsuitable temperature or lost seed viability. One failed test cannot diagnose seed dormancy.^[ref]

Initial seed water uptake, permitting renewed metabolism. Hydration does not prove seed viability or imply the idealized hydraulic law for capillary imbibition.^[ref]

A delayed, usually polarity-reversed copy of source radiation reflected at the water free surface. Interference with the direct wave shapes the usable spectrum; source depth controls the delay.

A propagating disturbance in or along the solid Earth, including body P waves, body S waves and surface modes. A water layer supports compressional acoustic motion but not a bulk shear restoring force.

For an ideal dilute chemical solution, moving one mole of a species with signed ion charge number $z$ from outside to inside changes its electrochemical potential byHere $R$ is the molar gas constant, $T$ the uniform absolute temperature, $F$ the Faraday constant, and $c$ the concentration. This assumes the same reference chemical potential on both sides. At thermodynamic equilibrium, $\Delta \tilde{\mu }=0$, henceThe Nernst equilibrium potential uses thermodynamic activities in the general case; replacing them by concentrations is an ideal-solution approximation.

Choose an original passive model: only ${\mathrm{K}}^{+}$ permeates ($z=+1$), other ions cannot cross, there are no pumps or imposed electric currents, and there is no net water transfer. Stipulate reservoir concentrations $c_{\mathrm{in}}=140\mathrm{mM}$ and $c_{\mathrm{out}}=5\mathrm{mM}$, with $T=310\mathrm{K}$, $R=8.314\mathrm{J}\mathrm{mo}{\mathrm{l}}^{-1}{\mathrm{K}}^{-1}$ and $F=96485\mathrm{C}\mathrm{mo}{\mathrm{l}}^{-1}$. Treat reservoir concentrations as effectively unchanged by charging. ThenThe concentration ratio is dimensionless; $J/C=\mathrm{V}$ supplies the voltage unit. At $V_m=0$, $\Delta \tilde{\mu }>0$ for inward transport, so outward transport is favored. At $V_m=E_{\mathrm{K}}$ it vanishes. A more negative $V_m$ favors inward transport. These sign checks explain the result physically.

Keeping the other chosen inputs fixed, doubling $c_{\mathrm{out}}$ to $10\mathrm{mM}$ raises $E_{\mathrm{K}}$ by $(RT/F)\ln 2\approx 18.52\mathrm{mV}$. Equal inside and outside concentrations give $E_{\mathrm{K}}=0$; reversing their ratio reverses its sign. In finite reservoirs, transport changes both concentrations; the exact final thermodynamic equilibrium must also satisfy material conservation. The fixed-reservoir calculation is useful when only a small fraction of the available ions moves.

A molecular layer formed through adsorption and lateral organization at a substrate. Anchoring groups, chain packing and exposed terminal chemistry jointly determine its properties. Hydroxyl-terminated alkanethiol films on gold provide a nonbiological example with controllable water wetting.

Two water molecules can exchange a proton, producing hydronium and hydroxide ions: $2{\mathrm{H}}_2\mathrm{O}\rightleftharpoons {\mathrm{H}}_3{\mathrm{O}}^{+}+{\mathrm{OH}}^{-}$. Even pure water therefore supplies ions; extreme dilution eventually invalidates the strong acid assumption that it supplies all the hydronium.

A semipermeable membrane ideally passes the solvent while excluding the specified solutes. In the aqueous osmosis model below, water can cross but the counted dissolved particles cannot. Real selective permeability is often a matter of different rates, so this idealization needs checking over the measurement interval. Neither an impermeable sheet nor a freely mixing opening realizes this model.^[ref]

Sensible heat is transferred heat associated with a temperature change within a single thermodynamic phase. By contrast, latent heat can change the phase fraction while the temperature stays fixed during equilibrium phase coexistence. Neither name denotes an additional stored substance: both describe how transferred heat participates in a process.

For fixed mass $m$ and composition, use the heat capacity appropriate to the heating constraint. Under the quasistatic process assumptions in heat capacity, with only pressure-volume work and unchanged bulk kinetic energy and potential energy, fixed-pressure heating givesHere $c_p$ is specific heat capacity at constant pressure; fixed-volume heating instead uses specific heat capacity at constant volume $c_V$. A cooling step has negative $Q_{\mathrm{sens}}$ with the sign convention in heat. A temperature difference has the same numerical value in units of the kelvin or degree Celsius. The integral follows by adding the small transfers $\delta Q=m{c}_p(T)dT$, rather than assuming a constant heat capacity.

As a stylized ice-to-water example for a fixed-composition closed system at fixed pressure $1\mathrm{atm}$, take $m=0.5\mathrm{kg}$, an initial temperature of $-10{}^{\circ }\mathrm{C}$, melting at $0{}^{\circ }\mathrm{C}$, and a final temperature of $20{}^{\circ }\mathrm{C}$. Assume constant specific heat capacity at constant pressure values $c_{\mathrm{ice}}=2.1\mathrm{kJ}\mathrm{k}{\mathrm{g}}^{-1}{\mathrm{K}}^{-1}$ and $c_{\mathrm{water}}=4.18\mathrm{kJ}\mathrm{k}{\mathrm{g}}^{-1}{\mathrm{K}}^{-1}$, and latent heat of fusion $L_f=334\mathrm{kJ}\mathrm{k}{\mathrm{g}}^{-1}$. These are stipulated, rounded model values; ignore the container and heat losses, retain all the material, and assume only pressure-volume work under the quasistatic process conditions above. The three steps areOnly the first and third terms are sensible heat; the middle term is latent heat. The plateau begins after $10.5\mathrm{kJ}$ and ends after $177.5\mathrm{kJ}$ of total supplied heat. At $94\mathrm{kJ}$ total input, half the mass is liquid water and the temperature remains $0{}^{\circ }\mathrm{C}$. The equilibrium phase transition temperature depends on pressure; this example stipulates a single fixed pressure. ^[ref]

This split makes heating budgets easy to interpret: melting consumes $167/219.3\approx 76.2\%$ of the supplied heat in this model despite causing no temperature rise. Within either single thermodynamic phase, the heating curve slope is $dT/dQ=1/(m{c}_p)$; a larger heat capacity makes the slope shallower. A flat interval represents changing phase fraction, so it cannot be modeled by applying $Q=m{c}_p\Delta T$ across the phase transition. The complementary constructed example in latent heat tracks that phase fraction explicitly.

Equivalent chemical bonds in an intact molecule need not have equal successive bond-dissociation enthalpies. Once one chemical bond is removed, the next reactant has a different electronic quantum state and may relax to a different molecular geometry. The successive steps compare different species. This distinction also explains why a tabulated average chemical bond strength is not necessarily the cost of the first cleavage.^[ref]

For an invented species $A{B}_2$, stipulate the following gas-phase steps, with all enthalpies at the same temperature and the same standard states:The symbols stand for hypothetical species with consistently chosen electronic states. They are not values for water or another measured molecule. By Hess's law, the total enthalpy of atomization for $A{B}_2(g)\to A(g)+2B(g)$ is $700\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$; the arithmetic mean per broken chemical bond is $350\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$. Neither individual step equals that mean. Nor must the second step be cheaper: here it is deliberately more expensive. An exact sequence sums exactly; substituting averages taken from other molecules generally gives only an estimate.

Mantle peridotite altered through reaction with water to form serpentine-bearing assemblages.