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A Assuming an altitude of 194 metres above mean sea level (the worldwide median altitude of human habitation), an indoor temperature of 23 °C, a dewpoint of 9 °C (40.85% relative humidity), and 760 mmHg sea level–corrected barometric pressure (molar water vapor content = 1.16%). B Calculated values *Derived data by calculation.
Accepted standardized value of the magnetic susceptibility of water at 20 °C (room temperature) is −12.97 cm 3 /mol. [27] Accepted standardized value of the magnetic susceptibility of water at 20 °C (room temperature) is −0.702 cm 3 /g. [27]
The concentration of water, [H 2 O], is omitted by convention, which means that the value of K w differs from the value of K eq that would be computed using that concentration. The value of K w varies with temperature, as shown in the table below. This variation must be taken into account when making precise measurements of quantities such as pH.
Water is the chemical substance with chemical formula H 2 O; one molecule of water has two hydrogen atoms covalently bonded to a single oxygen atom. [26] Water is a tasteless, odorless liquid at ambient temperature and pressure. Liquid water has weak absorption bands at wavelengths of around 750 nm which cause it to appear to have a blue color. [4]
These parameters are usually specified when giving the specific heat capacity of a substance. For example, "Water (liquid): = 4187 J⋅kg −1 ⋅K −1 (15 °C)." [11] When not specified, published values of the specific heat capacity generally are valid for some standard conditions for temperature and pressure.
Values for sodium chloride are typical for a 1:1 electrolyte. With 1:2 electrolytes, MX 2, pK w decreases with increasing ionic strength. [8] The value of K w is usually of interest in the liquid phase. Example values for superheated steam (gas) and supercritical water fluid are given in the table.
Another unit common in non-metric regions or sectors is the ton of refrigeration, which describes the amount of water at freezing temperature that can be frozen in 24 hours, equivalent to 3.5 kW or 12,000 BTU/h. [1] [2] [3]
The Btu should not be confused with the Board of Trade Unit (BTU), an obsolete UK synonym for kilowatt hour (1 kW⋅h or 3,412 Btu). The Btu is often used to express the conversion-efficiency of heat into electrical energy in power plants. Figures are quoted in terms of the quantity of heat in Btu required to generate 1 kW⋅h of electrical energy.