What is Henry’s Law?
Henry law explains the solubility of a gas in a liquid solution by partial pressure and mole fraction of the gas in the liquid.
Henry’s Law states that “the partial pressure applied by any gas on a liquid surface is directly proportional to its mole fraction present in a liquid solvent.”
The Mathematical Formula of Henry’s Law is as Follows –
P ∝ X
Where P = partial pressure applied by the gas on liquid in the solution
X = Mole fraction of gas in liquid
On Removing the Proportionality –
P = kH.X
Where kH is called Henry’s law constant.
What is Mole Fraction?
Mole fraction can be defined as a unit of concentration that is equal to the number of moles of a solute divided by the total number of moles of a solution. It is also called the amount fraction or molar fraction. Thus, the mole fraction of a gas (solute) in a solution of the gas in liquid can be written as follows –
Mole fraction of Gas in Liquid (X) = (Moles of gas (solute)) / Total Number Of Moles(solution)
As mole fraction is a ratio, it is a unitless expression.
When Pressure is Constant?
When pressure remains constant, according to henry’s law henry constant will be inversely proportional to the mole fraction of the gas. It can be represented as follows –
P ∝ X (Henry’s Law)
P = kHX
If P is constant, from the above equation can be written as –
X ∝
1kH
It means if the value of Henry's law constant decreases, the value of the mole fraction of gas in liquid increases. Mole fraction of the gas in liquid can be taken as solubility. Thus, as henry’s law constant decreases, the solubility of the solute in solution increases.
Relation of Henry’s Law Constant with Temperature
As we know, increasing the temperature solubility of the gas in liquid decreases. Thus, we can write a relation between temperature and solubility for gas in liquid solution as follows –
T ∝ 1/ Solubility - - - - - - (1)
According to henry’s law, we have explained above that if pressure is constant, as the value of henry’s law constant increases, the solubility of gas in liquid decreases. It can also be expressed as follow –
kH ∝ 1/Solubility - - - - - - (2)
From equations (1) and (2), we can write –
T ∝ kH
Factors affecting Henry’s Law Constant
Following Factors Affect the Henry’s Law of Constant of a Gas –
Nature of the gas. This is the reason different gases have different henry’s law constants in the solvent.
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Nature of the solvent
Temperature and Pressure of the system. This is the reason kH value is given differently for a gas at different temperatures.
Graph Between Solubility and Pressure (for Gas in Liquid Solution) According to Henry’s Law
Mathematical Expression of Henry’s Law can be Written as Follows –
P = kH.X _ _ _ _ _(3)
Where,
P = Partial pressure of the gas
X= mole fraction of gas in liquid
kH = Henry’s law constant
Equation (3) is the same as Y = MX which is a straight-line equation. So, the graph can be drawn as –
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Applications of Henry’s Law
The production of carbonated beverages is based on Henry’s law.
Hypoxia (concentration of oxygen is low in blood and tissues) can be explained by Henry’s law.
It is applied in deep-sea diving as well.
We can understand by Henry’s law that aquatic life survives better in cold water.
In soft drinks, it increases the CO2 solubility and adds flavour to the drinks.
Helps scuba divers to breathe at high pressure areas when air is diluted with He.
In areas where partial pressure of O2 is less, dissolution of o2 helps in breathing.
Limitations of Henry’s Law
It is applicable when the system is in equilibrium.
It is applicable for those gases only which do not react with water(solvent).
Gas shouldn’t cause any chemical change in the solution.
Henry’s law is appropriate only when pressure is not high, the temperature is not too low and gas is extremely soluble.
This was a brief of Henry’s Law, if you want to get solved numerically based on Henry's Law with a detailed explanation then register yourself on Vedantu or download the Vedantu learning app for class 6-10, IITJEE, and NEET.
FAQs on Henry's Law
1.Define the following terms related to the concept of 'henry's law' :
(i) Mole fraction
(ii) Solubility
(iii) Vapour pressure
(i) Mole fraction :
It is also called molar fraction and is represented by Xi.
In a system, the sum of the mole fraction is 1 every time. It is also called amount fraction and is identical to the number of molecules of a particle divided by the total number of all molecules in it.
It is commonly used in deriving the phase diagram and it is not dependent on temperature.
In this, the roles of 'solvent' and 'solute' can be reversed because its measure is symmetric.
In the case of an ideal gas mixture, partial pressure/total pressure gives the value of the mole fraction of the mixture.
(ii) Solubility :
The ability of the substance (solid, liquid, or gaseous) to dissolve in the solvent is called solubility.
Solubility gives the formation of a solution and is measured by determining the concentration of the saturated solution.
The concept of solubility is used everywhere and is a part of our basic life.
Everything that is seen around has solubility which leads to the formation of a solution.
In a cup of tea or coffee, Sugar cubes dissolve and provide sweetness to it, here sugar is 'soluble' in the tea to form a perfect solution where sugar is solute and tea/ coffee is solvent.
(iii) Vapour pressure :
It is the capability of the material to change into the gaseous or vapour state which leads to an increase in temperature.
When the vapour pressure (at the surface of liquid) equals the pressure exerted by the outside surroundings, it is known as the boiling point of the liquid and leads to the conversion of liquid to vapour.
Therefore, Evaporation of liquid is the main cause of the Vapour pressure of the liquid.
The vapour pressure can be affected by surface area, temperature, and intermolecular forces between the particles of liquid solution.
Vapour pressure has various industrial uses and it is also carried out in our day to day life.
2.What is partial pressure and explain its role in Henry's law?
Thermodynamic activity of the gas results in building the partial pressure between the particles. Here, acc. to Henry's law, P = KHC where P = partial pressure, KH = Henry's constant. Therefore, the partial pressure of a gas can be determined by knowing the value of the concentration of the dissolved gas.
For learning more about thermodynamics and partial pressure, students can refer to Vedant's free learning course. It provides PDF notes, MCQ series and other frequently asked questions related to various courses like NEET, JEE etc. These courses are designed in a way that makes understanding the concepts easier for students.
3.List out and describe the main differences between Henry's law and Raoult's law.
These are the points that explain the difference between Henry's law and Raoult's law :
Both of these laws are related to thermodynamics but Henry's law tells about the dissolution of a gas in a liquid medium whereas Roults's law expresses the relationship between the partial pressures of solutes and the vapor pressure of that same solution.
In Henry's law, the dissolved amount of gas in a liquid is proportional to the gas's pressure (partial pressure) when it is in equilibrium with that liquid. In Raoult's law, the product of the vapor pressure of pure solvent and the mole fraction of the solvent is equal to vapor pressure of a solvent above a solution.
Henry's law has the proportionality constant whereas Raoult’s law does not have any constant in its equation.
4.Explain the graph of Henry's law and list out the drawbacks.
The graph of Henry's law explains the proportionality between gas dissolved in solvent per unit volume and the equilibrium state pressure of the gas. Here K = proportionality constant in m=Kp
K depends on :
Nature of solvent
Gas nature
Temperature
pressure during reaction.
In Henry's law, the straight line signifies the validity of Henry’s law.
Also, x2 =K’ p2
p2 =K x2
because, ( K =1/K’ )
Here, x2 = mole fraction (gas)
p2 = partial pressure (gas)
K = henry's constant in henry's law.
Therefore, the graph between pressure and solubility depicts the proportionality between these quantities through the straight line.
Drawbacks of this graph representation :
In Henry's law, the temperature is not too low and the gas is dissolved completely.
Low amount of pressure.
5.Answer the following MCQ on 'henry's law' :
A). From the following gases, which gas is least soluble in water?
Sulphur dioxide
Ammonia
Nitrogen
Hydrogen chloride
Ans: c) Nitrogen
B). From the following relations, which one is incorrect?
∆T_b=(K_b×1000×W_2)/(M_2×W_1 )
∆T_f=K_f/m
∆T_f=(K_f×1000×W_2)/(M_2×W_1 )
∆T_b=K_b×m
Ans: d) ∆T_b=K_b×m (it explains the depression in the boiling point of liquid).
C). Which of the following applications does not belong to Henry’s law?
Bends suffered from Scuba divers
solubility of gases in water for making drinks.
Anoxia due to climbing
Cancer
Ans: d) Cancer.