Chemistry Formulas

Boiling Point Formula

The boiling point of a substance is that the temperature at which the vapour pressure of a liquid equals the pressure surrounding the liquid and therefore the liquid changes into a vapour. The boiling point of a liquid varies depending upon the encompassing environmental pressure. During this article, we’ll discuss the concept of boiling point and its boiling point formula with examples.

Concept of Boiling Point

The boiling point is that the temperature at which the pressure is exerted upon a liquid by the environment is equalled by the pressure exerted by the vapour of the liquid. Under this condition, the addition of warmth leads to the transformation of the liquid into its vapour without raising the temperature. A liquid has a lower boiling point. When that liquid is at air pressure during a partial vacuum, it has the lowest boiling point.

A liquid at high features a higher boiling point than when that liquid is at air pressure. For instance, water boils at 100 °C (212 °F) at sea level, but at 93.4 °C (200.1 °F) at 1,905 meters (6,250 ft) altitude. Different liquids will boil at different temperatures during a partial vacuum. The quality boiling point has been defined by IUPAC because the temperature at which boiling occurs under a pressure of 1 bar.

Boiling Point Formula

Source: en.wikipedia.org

Liquids may change to a vapor at temperatures below their boiling points through the method of evaporation. Evaporation is essentially a surface phenomenon during which molecules located near the liquid’s edge, escape into the environment as vapor. On the opposite hand, boiling may be a process during which molecules anywhere within the liquid escape, leading to the formation of vapor bubbles within the liquid.

Corresponding to the boiling point, the temperature at which the vapor pressure of the liquid equals the surrounding environmental pressure. Thus, the boiling point depends on the pressure. The boiling point increases with increased pressure. It is up to the critical point, where the gas and liquid properties become identical.

The Formula for Boiling  Point

It are often calculated as: Kb = RTb2M/ΔHv,

  • R is that the universal gas constant
  • Tb is that the boiling temperature of the pure solvent [in K]
  • M is that the molar mass of the solvent
  • ΔHv is that the heat of vaporization per mole of the solvent.

If the warmth of vaporization and therefore the vapor pressure of a liquid at a particular temperature is known then with the assistance of the Clausius–Clapeyron equation, the boiling point are often calculated as:

ln(P1/P2)=ΔHvap/R(1/T2 – 1/T1)

  • P1 and P2 are the vapor pressures
  • T1 and T2 are the temperatures
  • ΔHvap is that the Enthalpy (heat) of Vaporization and
  • R is that the universal gas constant (8.3145 J mol-1 K-1).

Solved Examples for Boiling Point Formula

Question – The boiling point elevation constant, kb, for CS2 is 2.3 (degrees celsius) and its boiling point is 46.3 (degrees Celsius). What would be the boiling point of a 1 tenth saturated solution of S8 in CS2? Calculate using Boiling Point Formula.

Solution – We’ve, ΔTb=Kb·bB

ΔTb is increasing within the boiling point and it’s defined as Tb (solution)-Tb (pure solvent).

We know, Kb = RTb2M / ΔHv

bB is the molarity of the solution

Therefore, (solution)= Tb (pure solvent)+ Kb·bB= 46.3 + 2.3*1/10 = 46.3+0.23 = 46.53 (degrees celsius)

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