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The relative permittivity (in older texts, dielectric constant) is the permittivity of a material expressed as a ratio with the electric permittivity of a vacuum. A dielectric is an insulating material, and the dielectric constant of an insulator measures the ability of the insulator to store electric energy in an electrical field.
A table of some typical values can be found under dielectric constant. Water has a relatively high dielectric constant value of 78.7 at 298K (25 °C), so in aqueous solutions at ambient temperatures 1:1 electrolytes such as NaCl do not form ion pairs to an appreciable extent except when the solution is very concentrated.
Dielectric constant [2] 88.00 at 0 °C 86.04 at 5 °C 84.11 at 10 °C 82.22 at 15 °C 80.36 at 20 °C 78.54 at 25 °C 76.75 at 30 °C 75.00 at 35 °C 73.28 at 40 °C 71.59 at 45 °C 69.94 at 50 °C 66.74 at 60 °C 63.68 at 70 °C 60.76 at 80 °C 57.98 at 90 °C 55.33 at 100 °C Bond strength: 492.215 kJ/mol O–H bond dissociation energy [3 ...
Water has a very high specific heat capacity of 4184 J/(kg·K) at 20 °C (4182 J/(kg·K) at 25 °C) —the second-highest among all the heteroatomic species (after ammonia), as well as a high heat of vaporization (40.65 kJ/mol or 2268 kJ/kg at the normal boiling point), both of which are a result of the extensive hydrogen bonding between its ...
In liquid water at high temperatures, (e.g. that approaching the critical temperature), the solubility of ionic solutes tends to decrease due to the change of properties and structure of liquid water; the lower dielectric constant results in a less polar solvent and in a change of hydration energy affecting the ΔG of the dissolution reaction.
2.4–2.7 Carbon disulfide: 2.6: BoPET: 3.1 [2] Paper, printing: 1.4 [3] (200 kHz) Electroactive polymers: 2–12 Mica: 3–6 [2] Silicon dioxide: 3.9 [4] Sapphire: 8.9–11.1 (anisotropic) [5] Concrete: 4.5: Pyrex : 4.7 (3.7–10) Neoprene: 6.7 [2] Natural rubber: 7: Diamond: 5.5–10 Salt: 3–15 Melamine resin: 7.2–8.4 [6] Graphite: 10 ...
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For one, polarizable liquids, such as water, have very high dielectric constant at low frequencies, when the molecules can follow the field, but not so high when they can't. Many materials commonly used as dielectrics don't have this change. For such liquids, a low frequency (DC limit) and high frequency (microwave to optical) region would be ...