Is Boiling Point A Physical Property: How, Why And Detailed Facts


In this article, we will discuss the properties of the boiling point and is boiling point a physical property or not with detailed facts.

A boiling point is a physical property of a matter because we can measure the temperature of the boiling liquid without perturbing the chemical properties of the liquid.

How Is Boiling Point a Physical Property?

The boiling point is a temperature at which the system changes its phase from one form to another.

The heat energy supplied to the liquid from the external sources is converted into thermal energy raising the temperature of the liquid which is measured using the thermometer, hence is a physical property of the liquids.

Is boiling point a physical property
Liquid to vapour phase on reaching the boiling point; Image Credit: Pixabay

The boiling point results in the change of the liquid state of the matter into the vapour state. This is evident due to the fact that the gap between the molecules increases, resulting in the physical change of the matter.

The boiling point leads to the change in the phase of the matter, and also the volume of the molecules occupying the space increases, and hence the density of the matter decreases.

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Is Change in Boiling Point a Physical Property?

The boiling point depends upon the chemical composition, density of molecules, and atmospheric pressure too.

If you lower the pressure at which the liquid boils then the boiling point of the liquid will be lowered; whereas if the exertion of pressure increases then liquid will start boiling at a higher temperature.

The boiling point is directly proportional to the pressure to which the system is exposed. So, according to Ideal Gas Law,

“The product of the volume of the molecules present in the system and the pressure incident upon the system is equal to the temperature of the system and the universal gas constant.”

This is given by the relation, PV=nRT

Where P is a pressure

V is a volume of the system

T is a temperature

R is a gas constant that is equal to 8.314 J/mol K

n is a number of moles

At constant temperature, the volume is inversely proportional to the pressure on the system. As the pressure increases, the volume of the system decreases. And at constant pressure, the volume of the system increases the heat energy required to raise the temperature of a system escalates.

The boiling point is related to the temperature and pressure by Clausius – Clapeyron equation as

Where TB is a temperature of boiling point

T is a temperature of a liquid

R is an ideal gas constant R=8.314 J/mol K

P is a vapour pressure

P0 is the pressure at temperature T

ΔHvap is a heat of vaporization

The heat of vaporization is the amount of heat required to convert the phase of the liquid to convert it into vapours.

We can frame the equation for the boiling point from this equation, hence we have

The change in the boiling point occurs due to the variations in the pressure, which is a physical property. Also, there are no variations in the chemical properties of the liquid or any other changes seen in the matter. Hence, the change in the boiling point is evidently a physical property of the liquid.

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How Is Change in Boiling Point a Physical Property?

The boiling point of the liquid can be measured and the variation in the boiling point can also be determined.

The change in boiling point occurs due to a change in the pressure or adding impurities to the volume of a liquid. But the boiling point doesn’t bring any variations in a liquid although it elongates the distance of separation between the molecules.

The physical properties of the matter can be measured or noticed without changing any chemical properties of the matter. Upon exposing the system to the external heat source, the heat energy is converted into thermal energy. The molecules constituting the liquid, move further and further away from each other, reducing the density of the system per unit volume of the liquid. This energy is acquired by the molecules and escapes in the air gaining enough potential energy.

Read more on Physical Irreversible Change Example: Detailed Analysis.

What is a change in the boiling point of the water on adding a pinch of sodium chloride weighing 15 grams?

We know that the boiling point of water is 100 degrees Celsius and atmospheric pressure is 1atm.

The atomic mass of cation of salt Na is 22.99 g

The atomic mass of an anion of salt Cl is 35.45 g

Hence the atomic mass of sodium chloride salt is 22.99+35.45 = 58.44 grams

The moles of NaCl added to the boiling water is

Moles of NaCl= 15g x 1 mole/58.44g

Moles of NaCl= 0.2567 mole

If the volume of the water in a beaker is 100ml, then the mass of the water is

M = ϱV

M = 1 x 100 =100 grams = 0.1kg

The molality of solute in solvent is

m = moles of solute/mass of solvent

m = 0.2567/0.1= 2.567 mol/kg

Hence, the variation seen in the boiling point of the water is

ΔT=ikbm

Here, in this case, Van’t Hoff factor i=2 because two ions of sodium and chlorine will dissociate in water.

ΔT=2 x 0.51 x 2.567=2.620C

The variation in the boiling point temperature of the water we have calculated is 2.620C.

Hence, the boiling point of the water on mixing 15 grams of sodium chloride in 100 ml of water will be 100+2.62= 102.620C.

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Frequently Asked Questions

Calculate the temperature of the boiling point of a liquid having a temperature of 60 degrees building a vapour pressure of 1.2 atm. The heat of vaporization is 1420 J/g.

Given: T =600 C

R = 8.314 J/mol K

P =1.2 atm

P0 =1 atm

ΔHvap=1420 J/g

The equation to find the boiling point is

Inserting all the given values in this equation we get

= ((16.67 – 1.06) x 10-3 )-1

= (15.61 x 10-3 )-1

=103/16.23

=64.060 C

Hence, the boiling point of the liquid is 64.060C.

Does the boiling point of the liquid vary on adding salt?

The ice-cream parlor uses salt to maintain the temperature to a freezing point to prevent ice cream from heeling.

On adding a grain of salt to the liquid, the temperature of the liquid is slightly lowered as the heat energy from the surrounding is absorbed by the salt and more time is required to reach the temperature at the boiling point.

Does the boiling point of the liquid change due to the presence of impurities?

The presence of impurities varies the boiling point of the liquid.

The heat energy supplied to the liquid is grasped by the particles of impurities present in the liquid and hence the boiling temperature of the liquid may increase.

What is an effect on the boiling point if the pressure increases?

Pressure is directly related to the temperature of the system.

As the pressure increases, the temperature required for the liquid to boil will also increase, thus raising the boiling point of the liquid.

AKSHITA MAPARI

Hi, I’m Akshita Mapari. I have done M.Sc. in Physics. I have worked on projects like Numerical modeling of winds and waves during cyclone, Physics of toys and mechanized thrill machines in amusement park based on Classical Mechanics. I have pursued a course on Arduino and have accomplished some mini projects on Arduino UNO. I always like to explore new zones in the field of science. I personally believe that learning is more enthusiastic when learnt with creativity. Apart from this, I like to read, travel, strumming on guitar, identifying rocks and strata, photography and playing chess. Connect me on LinkedIn - linkedin.com/in/akshita-mapari-b38a68122

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