Vapor Pressure | Raoult's Law | Solution Class 12

Summary

This video explains key concepts related to vapor pressure and Raoult's law, starting with the distinction between volatile and non-volatile substances. It covers evaporation, vapor pressure in closed containers, and the equilibrium between evaporation and condensation. The video delves into how temperature and intermolecular forces influence vapor pressure. It introduces Raoult's law, describing how partial vapor pressure is directly proportional to mole fractions in a solution. The video concludes with applications of Raoult's law, solving problems on total vapor pressure using Dalton's law, and includes numerical examples for clarity.

Takeaways

• 🌡️ Volatile substances, such as water, gasoline, and ethanol, evaporate at temperatures above or below room temperature, whereas non-volatile substances like salt and sugar do not.
• 💧 Evaporation is the process where surface molecules of a liquid, which have higher kinetic energy, escape and become vapor.
• 🔄 The difference between evaporation and boiling is that boiling occurs at a fixed temperature, while evaporation can happen at any temperature.
• 💭 Vapor pressure is defined as the pressure exerted by vapors on the surface of a liquid in a closed container and is a result of evaporation within that container.
• 🔆 Temperature has a direct relationship with vapor pressure; as temperature increases, so does vapor pressure.
• 🔗 The nature of the liquid and its intermolecular forces inversely affect vapor pressure; liquids with weaker intermolecular forces have higher vapor pressures.
• 🌀 Raoult's Law states that the partial vapor pressure of a liquid in a solution is equal to the vapor pressure of the pure liquid multiplied by its mole fraction in the solution.
• 📉 Dalton's Law is used to calculate the total vapor pressure of a solution, which is the sum of the partial vapor pressures of each volatile component in the solution.
• 📊 Graphically, Raoult's Law can be represented by a straight line where the vapor pressure of a liquid is directly proportional to its mole fraction.
• 🧪 Numerical problems involving Raoult's Law involve calculating the partial vapor pressure of solvents in solutions using their mole fractions and pure vapor pressures.

Q & A

What is a volatile substance?

A volatile substance is one that evaporates into a gas at room temperature or higher. Examples include water, gasoline, and ethanol.

What is the difference between volatile and non-volatile substances?

Volatile substances evaporate at room temperature or below, such as water and ethanol, while non-volatile substances, like salt and sugar, do not evaporate at these conditions.

What is evaporation?

Evaporation is the process by which a liquid transforms into vapor. It occurs when surface molecules with high kinetic energy escape from the liquid into the air.

How is evaporation different from boiling?

Boiling occurs at a fixed temperature (e.g., 100°C for water), while evaporation can occur at any temperature, even as low as 0°C.

What is vapor pressure?

Vapor pressure is the pressure exerted by the vapors of a volatile liquid on the surface of the liquid when in a closed container at a given temperature.

How does temperature affect vapor pressure?

There is a direct relationship between temperature and vapor pressure. As temperature increases, vapor pressure also increases, such as water at 60°C having a higher vapor pressure than at 40°C.

What are the factors affecting vapor pressure?

Two main factors affect vapor pressure: temperature (direct relationship) and the nature of the liquid (inverse relationship with intermolecular forces).

What is Raoult’s Law?

Raoult’s Law states that the partial vapor pressure of a liquid in a solution is directly proportional to the mole fraction of that liquid in the solution.

How do you calculate total vapor pressure in a solution?

Total vapor pressure of a solution can be found using Dalton’s Law, which states that it is the sum of the partial vapor pressures of all the volatile components in the solution.

What is the difference between Raoult's Law and Dalton's Law?

Raoult’s Law explains the partial vapor pressure of a single volatile component in a solution, while Dalton’s Law is used to find the total vapor pressure of a solution by summing all partial pressures.

Outlines

00:00

💧 Understanding Vapor Pressure and Evaporation

This section introduces the fundamental concepts of vapor pressure and evaporation. It distinguishes between volatile and non-volatile substances, using water, gasoline, and ethanol as examples of the former, and salt, sugar, and urea as examples of the latter. The script explains evaporation as a process where surface molecules with higher kinetic energy escape from the liquid to become vapor. It contrasts evaporation with boiling, highlighting that boiling occurs at a fixed temperature, whereas evaporation can happen at any temperature. The concept of vapor pressure is then introduced as the pressure exerted by vapors on the surface of a liquid in a closed container, reaching equilibrium when the rate of evaporation equals the rate of condensation.

05:03

🔍 Factors Affecting Vapor Pressure

The second paragraph delves into the factors that influence vapor pressure. It establishes a direct relationship between temperature and vapor pressure, illustrating that water at 60 degrees Celsius has a higher vapor pressure than at 40 degrees Celsius. It also discusses the nature of the liquid and its intermolecular forces, showing an inverse relationship with vapor pressure. Using water and acetone as examples, it explains that acetone has a higher vapor pressure at 40 degrees Celsius due to its weaker intermolecular forces compared to water's strong hydrogen bonding. The paragraph reinforces the understanding that vapor pressure is also known as equilibrium vapor pressure and is independent of the shape of the container.

10:05

🌡️ Vapor Pressure of Pure and Binary Liquids

This part of the script teaches the concept of vapor pressure for pure liquids (P naught) and binary liquids. It describes how a pure liquid in a closed container will exert vapor pressure over time and how combining two liquids in one container results in a solution with each liquid exerting partial pressure. The difference between the vapor pressure of a pure liquid (P naught) and the partial pressure (P) of a liquid in a solution is clarified. The script then introduces Raoult's Law, stating that the partial vapor pressure of a liquid in a solution is directly proportional to its mole fraction in the solution. The law is applied to calculate the partial vapor pressures of both liquids in a solution.

15:06

📊 Graphical Representation of Raoult's Law

The fourth paragraph provides a graphical representation of Raoult's Law. It describes how to plot vapor pressure against mole fraction for two volatile liquids, with one being more volatile than the other. The script explains that as mole fraction decreases from left to right on the x-axis, the partial vapor pressure also decreases for the first liquid, while it increases for the second liquid. The resulting graph consists of two straight lines representing the partial vapor pressures of each liquid in the solution. The total vapor pressure of the solution is the sum of the partial vapor pressures of both liquids.

20:07

📚 Application and Numerical Problems of Raoult's Law

The final paragraph applies Raoult's Law to solve numerical problems related to vapor pressure. It presents a scenario where glucose is added to water and calculates the partial vapor pressure of water in the resulting aqueous solution. The calculation involves determining the number of moles of each component and applying Raoult's Law to find the partial vapor pressure of water. Another example involves an ideal solution of ethanol and methanol, where the total vapor pressure is calculated by summing the partial vapor pressures of each component, determined using their respective mole fractions and pure vapor pressures.

Keywords

💡Volatile Substances

Volatile substances are materials that evaporate easily at room temperature due to having high vapor pressure. In the video, examples such as water, gasoline, and ethanol are given, showing how they evaporate and form vapors. This concept is fundamental to understanding vapor pressure, as it is these substances that generate vapor pressure when enclosed.

💡Non-Volatile Substances

Non-volatile substances are materials that do not evaporate easily at room temperature because they have low vapor pressure. Examples like salt, sugar, and urea are provided in the video. These substances help contrast the behavior of volatile substances, as non-volatile substances do not contribute significantly to vapor pressure.

💡Evaporation

Evaporation is the process by which surface molecules of a liquid escape into the air as vapor. It occurs only in volatile substances. In the video, it is explained how molecules with higher kinetic energy escape from the surface of the liquid into vapor form. Evaporation happens even at temperatures lower than the boiling point, making it a key concept in understanding how vapor pressure develops.

💡Vapor Pressure

Vapor pressure is the pressure exerted by vapor molecules when they strike the surface of a liquid in a closed container. The video describes vapor pressure as the result of volatile liquids evaporating in an enclosed space. At equilibrium, vapor pressure is constant, and it reflects the balance between evaporation and condensation. The concept is central to the discussion of how liquids behave in different conditions.

💡Boiling Point

The boiling point is the temperature at which a liquid's vapor pressure equals the external pressure, causing it to boil. The video contrasts evaporation with boiling, emphasizing that boiling occurs at a fixed temperature, while evaporation can happen at any temperature below the boiling point. Water’s boiling point, for example, is given as 100°C.

💡Equilibrium

Equilibrium in this context refers to the point at which the rate of evaporation equals the rate of condensation in a closed system. The video explains that at equilibrium, the number of molecules evaporating is the same as the number condensing, resulting in a stable vapor pressure. This balance is a critical part of understanding how vapor pressure is maintained in a system.

💡Intermolecular Forces

Intermolecular forces are the forces of attraction or repulsion between molecules. In the video, these forces are discussed as a factor influencing vapor pressure, with weaker intermolecular forces (like those in acetone) leading to higher vapor pressure, while stronger forces (like hydrogen bonding in water) result in lower vapor pressure. Understanding these forces helps explain why different substances have different vapor pressures.

💡Raoult’s Law

Raoult’s Law describes how the partial vapor pressure of a liquid in a solution is proportional to its mole fraction. In the video, Raoult’s Law is used to calculate the partial vapor pressures of different volatile liquids in a solution. This law is essential for understanding how the vapor pressures of individual components contribute to the overall vapor pressure of a mixture.

💡Partial Vapor Pressure

Partial vapor pressure refers to the pressure exerted by a single component of a mixture in a solution. The video explains that in a solution of two volatile liquids, each liquid exerts its own partial vapor pressure, which can be calculated using Raoult’s Law. This concept helps in determining how each liquid contributes to the total vapor pressure of the system.

💡Dalton’s Law

Dalton’s Law states that the total vapor pressure of a solution is the sum of the partial pressures of all volatile components. The video contrasts Raoult’s Law with Dalton’s Law, showing that while Raoult’s Law explains partial vapor pressure, Dalton’s Law is used to calculate the total vapor pressure in a solution with multiple volatile liquids.

Highlights

Definition of volatile substances that evaporate at room temperature or below.

Definition of non-volatile substances that do not evaporate at room temperature or below.

Explanation of evaporation as a process occurring in volatile substances like water.

Description of the kinetic energy difference between surface and bulk molecules in a liquid.

Evaporation defined as the transformation of a liquid into vapors due to high kinetic energy of surface molecules.

Difference between evaporation and boiling point clarified, with boiling occurring at a fixed temperature.

Introduction to vapor pressure as evaporation within a closed container.

Vapor pressure defined as the pressure exerted by vapors on the surface of a liquid at a given temperature.

Factors affecting vapor pressure include temperature and the nature of the liquid or intermolecular forces.

Vapor pressure does not depend on the shape of the container.

Concept of vapor pressure of pure liquids (P naught) explained.

Introduction to partial vapor pressure in solutions containing more than one volatile liquid.

Definition of partial vapor pressure as the pressure exerted by one liquid in a solution.

Explanation of Raoult's Law stating that the partial vapor pressure of a liquid in a solution is directly proportional to its mole fraction.

Graphical representation of Raoult's Law showing the relationship between vapor pressure and mole fraction.

Application of Raoult's Law in calculating the partial vapor pressure of liquids in a solution.

Difference between Raoult's Law and Dalton's Law in calculating total vapor pressure of a solution.

Numerical problem-solving using Raoult's Law to find the vapor pressure of aqueous solutions.

Numerical problem-solving using Raoult's Law to calculate the total vapor pressure of a solution containing ethanol and methanol.

Transcripts

vapor pressure and routes law firstly we

will learn some basic concepts like

volatile substances and non-volatile

substances a volatile substance is one

that evaporates into a gaze through

temperature or below for example water

gasoline ethanol Etc are all volatile

substances

while non-volatile substances is the one

that doesn't evaporate into a gaze at

room temperature or below for example

salt sugar

urea Etc are all non-volatile substances

the second concept is evaporation

remember that evaporation only occurs in

volatile substances like water now

consider this open object which contains

water we know that the molecules at the

surface are called surface molecules and

the molecule inside are at the bottom

are called bulk molecules the bulk

molecules have low kinetic energy due to

which they move slowly

while the surface molecules have high

kinetic energy due to which they move

fast now listen carefully after some

time the surface molecules would leave

the liquid and would Escape into the

vapors

let me repeat it after some time the

surface molecules would leave the liquid

and would Escape into the vapories this

process is known as evaporation

if you ask me why these surface

molecules leave the liquid the answer is

simple it is because they have high

kinetic energy due to which they leave

the liquid surface and become Vapors

therefore we Define evaporation as the

process by which a liquid is transformed

into Vapors is called evaporation

here let me ask you one important

question what is the difference between

evaporation and boiling point

well boiling occurs at fixed temperature

for example the boiling point of water

is fixed which is 100 degree Centigrade

while evaporation can occur at any time

pressure

for example water can even evaporate its

0 degree centigrade

just remember that every volatile liquid

evaporates at any temperature

now let me teach you the basic concept

of vapor pressure if I teach the

complete concept of vapor pressure in

one statement then I would say vapor

pressure is evaporation in a closed

container this statement explain the

whole philosophy of vapor pressure now

consider this close container which

contain a volatile liquid

we already know that volatile liquid

evaporates I mean these surface

molecules convert into vapor due to high

kinetic energy hence I write evaporation

occurs and which surface molecules

evaporate into vapories

after some time these Vapors would

condense and would fall back into the

liquid

hence I write condensation occurs in

which Vapors convert to liquid here

inside this close container evaporation

occurs I mean liquid converts to Vapor

secondly condensation occurs I mean

Vapors convert to liquid now a time will

reach when rate of evaporation would be

equal to the rate of condensation this

stage is called equilibrium

to make this concept more simple we say

that at equilibrium if 10 molecules of

liquid evaporates into vapories then 10

molecules of vapor condensed into liquid

now listen carefully here I am going to

teach you the best part of vapor

pressure which a lot of talented people

are missing

we know that these Vapors condense and

fall back into the liquid

when these Vapors fall back into the

liquid surface they exert force or unit

area of the liquid surface let me repeat

it when these Vapors fall back into the

liquid surface they exert force on unit

area of the liquid surface

we know that pressure is equal to force

on a unit area this pressure is exerted

by the vapors so we call it vapor

pressure

remember that vapor pressure is the

pressure of vapors on the surface of

liquid therefore we Define vapor

pressure as the pressure exerted by

Vapors on the surface of the liquid at a

given temperature is called vapor

pressure let me repeat it the pressure

exerted by Vapors on the surface of the

liquid at a given temperature is called

vapor pressure remember that vapor

pressure is also known as equilibrium

vapor pressure

hence notary down that the pressure of

vapors on the surface of liquid is

called vapor pressure

now let me teach you factors affecting

vapor pressure

first Factor affecting vapor pressure is

temperature there is direct relationship

between temperature and vapor pressure

for example water is 60 degree

Centigrade has more vapor pressure than

water at 40 degree centigrade

the second factor is nature of liquid or

intermolecular forces there is inverse

relationship between intermolecular

forces and vapor pressure

for example consider water and acetone

at 40 degree Centigrade the vapor

pressure of acetone is more than water

because acetone has weak intermolecular

forces like London dispersion forces

while the water has strong

intermolecular forces like hydrogen

bonding also remember that vapor

pressure doesn't depend upon the shape

of objects

hence noted down all these important

points

now we will learn the most important

concept of this lecture

firstly we will learn the vapor pressure

of pure liquid P naught remember that I

take volatile liquids now consider first

liquid in this closed container and

secant liquid in this close container

this container contains one type of

molecules and this container also

contains one type of molecules after

some time the volatile liquid will exert

vapor pressure on the surface of the

liquid

we write vapor pressure of pure liquid 1

is equal to P1 naught

similarly the volatile liquid in the

second container would exert vapor

pressure on the surface of the liquid

we write paper pressure of pure liquid 2

is equal to P2 naught

hence we learned that e naught is the

vapor pressure of pure liquid or the

vapor pressure of only one liquid

let me repeat this important point

P naught is the vapor pressure of pure

liquid or the vapor pressure of only one

liquid

hence noted down this very very

important point

now let me teach you the Weber pressure

of binary liquids are two liquids

consider liquid number one and liquid

number two enclosed container from the

previous example we know that vapor

pressure of pure liquid 1 is equal to P1

naught

and the vapor pressure of pure liquid 2

is equal to P2 naught now I combine

these two liquids in one closed

container I get a solution

this solution contains two volatile

liquids liquid number one and liquid

number two I mean this solution contains

two types of different molecules

now listen carefully and the solution

liquid one exert partial pressure P1 and

liquid to exert partial pressure P2 let

me repeat it

and the solution liquid 1 exert partial

pressure P1 and liquid to exert partial

pressure P2

here let me ask you one of my favorite

questions what is the difference between

P1 naught and P1 can you guess the

answer

well it is super easy P1 naught is the

vapor pressure of pure liquid one

for example P1 naught is the vapor

pressure of pure liquid and this

container while P1 is the partial

pressure of liquid 1 and a solution

for example E1 is the partial pressure

of liquid one and this container of

solution

similarly P2 naught is the vapor

pressure of pure liquid 2 and P2 is the

partial pressure of liquid number two

and a solution

now what is meant by partial vapor

pressure well partial vapor pressure

means pressure of one liquid and a

solution for example here are two

liquids in this solution

P1 is the partial vapor pressure of

liquid one and P2 is the partial vapor

pressure of liquid number two

hence noted down all these important

points

now let me ask you the most important

question of this lecture

how can we find the partial vapor

pressure of P1 and partial vapor

pressure of P2 and a solution

well to find partial vapor pressure in a

solution here comes the routes Baba he

states that partial vapor pressure of

any liquid is directly proportional to

mole friction of that liquid and a

solution

so we write partial vapor pressure of P1

in a solution is directly proportional

to its mole fraction X1

if you want to learn more about mole

friction then watch our video and its

link is given in the description

now to eliminate the sign of

proportionality we have to put some sort

of constant

let this Escape I write partial vapor

pressure of liquid 1 is equal to K into

its mole fraction let this is equation

number one

remember that mole friction of liquid 1

x 1 is equal to number of moles of

liquid 1 upon number of moles of liquid

1 less number of moles of liquid two now

we will find the value of constant k

let's consider only liquid 1 in this

container its mole friction X1 is equal

to 1. now the vapor pressure of pure

liquid is P1 naught is equal to K into

its mole friction

our P1 naught is equal to K N to 1 we

get P1 naught is equal to K

that this is equation number two now I

plug in equation number to n equation

number one I get P1 is equal to P 1

naught into its mole friction it means

that partial vapor pressure of liquid 1

in a solution is equal to vapor pressure

of pure liquid 1 and to its mole

friction

similarly partial vapor pressure of

liquid to NS solution is equal to vapor

pressure of pure liquid number 2 and to

add small friction in a solution

therefore we Define route's law as

partial vapor pressure of a liquid or

solvent and a solution is equal to the

vapor pressure of pure solvent and its

mole friction in a solution

let me repeat it

partial vapor pressure of a liquid are

solvent in a solution is equal to the

vapor pressure of pure solvent into its

mole friction in a solution

thus we learned that routes law explain

the partial pressure of a volatile

liquid in a solution

hence noted down this important concept

now let me teach you the application of

routes law

well consider the solution of liquid

number one and liquid number two from

the previous example we know that there

are two types of volatile liquids in

this solution we already learned that

route slow helps us to find the partial

vapor pressure of liquid number one in a

solution which is P1 is equal to P1

naught into its mole friction and routes

law helps us to find the partial vapor

pressure of liquid number 2 which is P2

is equal to P2 not into its small

friction

so let me ask you can routes law find

the total vapor pressure of a solution

the answer is no route slope cannot

explain or find the total vapor pressure

of a solution it can only find or

explain the partial vapor pressure of

one liquid or one component in a

solution

now the second question is then how can

we find the total vapor pressure of a

solution

well with the help of delton's law we

can find the total vapor pressure of a

solution the total vapor pressure of a

solution is equal to partial vapor

pressure of first Liquid Plus partial

vapor pressure of second liquid this

remember that route slow explains the

partial vapor pressure of one liquid in

a solution and delton's law explained

the total vapor pressure of a solution

hence noted down this basic difference

between routes law and deltan's law now

I will teach you graphical

representation of routes law let's

consider two volatile liquids liquid

number one and liquid number two

let liquid number one is more volatile

than liquid number two according to

routes law vapor pressure of quid number

one P1 is directly proportional to its

mole friction

similarly vapor pressure of quid number

two P2 is directly proportional to its

mole friction

now I will teach you the graph of routes

law using my personal method I draw two

vertical arrows or y-axis we take vapor

pressure on y-axis

secondly I draw a horizontal line or x

axis

we take more friction on x-axis

that this is the left side and this is

the right side of x-axis

let I take more friction of first liquid

at left side and more friction of second

liquid at the right side

now I will write some important points

believe me no one can teach you these

magic lines

I write from left to right along x axis

mole friction of first liquid decreases

we know that when mole friction

decreases partial vapor pressure P1 also

decreases

if more friction are first liquid X1 is

1 here then mole friction of first

liquid is 0 there because it is

constantly decreasing along x axis

now this is the vapor pressure of first

liquid which is P1 naught we know that

both friction of first liquid decreases

from left to right

here partial vapor pressure P1 also

decreases and we get this straight line

it is partial vapor pressure P1 of

liquid one

secondly from left to right mole

friction of secant liquid increases we

know that if more friction of second

liquid is 0 here then its mole friction

is 1 there

we also know that pure vapor pressure of

secret liquid P1 naught is here because

it is less volatile than first liquid

now from left to right mole friction or

second liquid increases hence partial

vapor pressure of second liquid also

increases

I draw this straight line it is the

partial vapor pressure P2 of liquid

number two now what about total vapor

pressure of the solution

well this is the total vapor pressure of

the solution e total is equal to T1 plus

P2

hence rotate down this graphical

representation of routes law

finally let me teach you some important

numerical problems from je main exam

consider this question 18 gram of

glucose is added to

178.2 gram water find the vapor pressure

of water and Tor for the aqueous

solution firstly I write the given data

the given mass of glucose is 18 gram and

the given mass of water is

178.2 gram here is one important fact

which you must know and it is not given

in the question the vapor pressure of

pure water PW naught is equal to

760 torr now according to routes law

partial vapor pressure of water in this

aqueous solution is PW is equal to its

pure pressure and to its mole friction

our PW is equal to PW naught N2 number

of moles of water upon number of moles

of water plus number of moles of glucose

here I will calculate the molar mass of

glucose and molar mass of water the

molar mass of glucose is equal to 6

carbon plus 12 hydrogen plus 6 oxygen R

6 into 12 plus 12 into 1 plus 6 into 16.

I get 180 gram per mole we know that the

molar mass of water is 18 gram per mole

now I will calculate the number of moles

the number of moles of glucose is equal

to given Mass which is 18 gram upon

molar mass which is 180 gram per mole

after calculation I get 0.1 mole

secondly the number of moles of water is

equal to

178.2 gram upon 18 gram per mole after

calculation I get

9.9 moles now we know that the vapor

pressure of pure water PW naught which

is 760 tall

secondly we know that the number of

moles of water and wo which is 9.9 mole

thirdly we know that the number of moles

of glucose NG which is 0.1 mole

so I will plug in all these three values

in this equation

after calculation I get

752.4 tar

hence the partial vapor pressure of

water and this solution is

752.4 tall

so note it down this important numerical

problem

finally consider this another question

from je main exam

the vapor pressure of ethanol and

methanol are 44.5 and 88.7 mmhg an ideal

solution is formed by mixing 60 gram of

ethanol and 40 gram of methanol at the

same temperature calculate the total

vapor pressure of the solution

well I write the given data the given

vapor pressure of pure ethanol p e

naught is equal to

44.5 mm he the given vapor pressure of

pure methanol PM naught is equal to

88.7 mm HG

the given mass of ethanol is 60 gram and

the given mass of methanol is 40 Gram

now the required value is the total

vapor pressure of solution we know that

total vapor pressure is equal to partial

pressure of ethanol plus partial

pressure of methanol

no I will find the molar mass of ethanol

and methanol we know that the molar mass

of ethanol is

c2h5oh two carbon plus 5 hydrogen plus

oxygen plus hydrogen 2 into 12 plus 5

into 1 plus 16 plus 1 I get 46 gram per

mole

secondly the molar mass of methanol is

carbon plus three hydrogen plus oxygen

plus hydrogen are 12 plus 3 into 1 plus

16 plus 1 which is equal to 32 gram per

mole now I will find the number of moles

the number of moles of ethanol is equal

to given Mass which is 60 gram upon

molar mass which is 46 gram per mole I

get 1.3 mole the number of moles of

methanol is equal to given Mass which is

40 gram upon molar mass which is 32 gram

per mole I get 1.25 mole now I will find

the partial vapor pressure of ethanol PE

which is equal to p e naught into its

mole friction

our PE is equal to p e naught number of

moles of ethanol upon total number of

moles

we know that vapor pressure of pure

ethanol is 44.5 mm-hg the number of

moles of ethanol is 1.25 upon total

number of moles

after calculation I get partial vapor

pressure of ethanol is equal to

21.8 mmhg

secondly I find the partial vapor

pressure of methanol PM which is equal

to PM naught and to its mole friction

RPM is equal to PM naught and to number

of moles of methanol upon total number

of moles we know that the vapor pressure

of pure methanol is 88.7 number of moles

of methanol is 1.3 upon total number of

moles

after calculation I get partial vapor

pressure of methanol is equal to

44.35 mm HG

finally I put partial vapor pressure of

ethanol and partial vapor pressure of

methanol and this equation number one I

write total vapor pressure of the

solution is equal to

21.8 mm-hg plus

44.35 mmhg after calculation I get

66.15 mmh GE thus the total vapor

pressure of this solution is

66.15 mmhg hence noted down the second

numerical problem

I hope that you have learned all about

vapor pressure and routes law