basic rules and laws of science for food technology

8/10/2019 Basic rules and laws of science for food technology

1/22

Basic rules and Laws

BPE

CAFODAT1stSEM


2/22

Yesterdays Recap

Boyles law

Charles law


3/22

LAW

RELAT-

IONSHIP

LAW

CON-

STANT

oyles

P V

P

1

V

1

= P

2

V

2

T n

harles

V T

V

1

/T

1

= V

2

/T

2

P n
http://localhost/var/www/apps/conversion/tmp/Local%20Settings/Temporary%20Internet%20Files/Content.IE5/6M06IQCW/Combined%20and%20ideal%20gas%20laws.ppt


4/22

Todays lesson

Gas laws

Combined gas law

Avogadros law Ideal gas equation

Numerical value of R

Daltons law of partial pressure

Units and dimensions


5/22

Combined gas law

Boyles law relates pressure and volume, while

Charles law related volume and temperature

at constant pressure.

By combining these two laws, we can get

combined gas law equation which shows that

how the volume of a given mass of gas

changes with simultaneous change oftemperature and pressure.


6/22

Combined gas law

According to Boyles law, for a given mass of gas,

V 1/P when temperature is constant(1)

According to Charles law,V T when pressure is constant..(2)

Combining Boyles and Charles law,

V T/P when temperature and pressure vary.(3)Or V =KT/P

Or PV/T = K, where K is a constant(4)


7/22

Combined gas law

Let P1, V1and T1be initial and P2, V2and T2

final pressure, volume, and temperature of a

given mass of gas respectively. Then,

P1V1/T1= P2V2/T2(5)

With the help of this equation, it is possible to

convert the volume of a given mass of gas

from one set of conditions to another.


8/22

Combined gas law

The equation (4) is,

PV/T =K

Or PV=KT

Where K is a constant and its value depends upon the massof gas taken. If 1 gram of the gas is taken, then K is knownas specific gas constant and its value differs from one gasto another. If one mole of a gas, is taken then instead of K,the symbol R is used and its value is the same for all gases,hence called Universal Gas Constant. For 1 mole of a gas,the equation 4 becomes,

PV= RT.(6)


9/22

Combined gas law

If the pressure of the gas is expressed in atmosphereand volume of the gas in litre the value of R is equal to0.0821 L Atm/K mol

If n moles of gas is taken then the equation (6) takes the

form,PV =nRT(7)

This equation is known as the Ideal Gas Equation, since

this equation is strictly valid only to ideal gas at alltemperature and pressure.


10/22


What is R?

Calculate the numerical value of R? (2)


11/22


In ideal gas equation is given by;

PV =nRT

Where P= pressure, V=volume of gas, R=Universal

gas constant, T=Temperature

One mole of gas at NTP occupies 22.4 liters. Hence,

the value of R can be calculated as follows,

R= PV/nT = 1atmx22.4liter/1molex273K

= 0.0821 liter-atm mole-1K-1


12/22

Avogadros Law


13/22

Avogadros Law

Avogadro's law is a gas law named after Amedeo

Avogadro who, in 1811,hypothesized that two given

samples of an ideal gas, at the same temperature,

pressure and volume, contain the same number ofmolecules. Thus, the number of molecules or atoms

in a specific volume of gas is independent of their

size or the molar mass of the gas.

O2 N2 CO2


14/22

Avogadros Law

Avogadro's law is stated mathematically as

V n (number of moles) or V =k n

V/n = kWhere, V= volume of gas, n = the amount of gas

, k =proportionality constant.

For two different gases,V1/n1= V2/n2


15/22

Conclusions from Avogadro's law

1) The volume of a gas is directly proportionalto thenumber of molecules (moles)of gas at the same T and P.

2) 2) One mole of any gas occupies the same volume for a

given T and Pand contains the same number of particles

- atoms - molecules.

3) 3) This volume is called the molar volume and is 22.414

Lfor an ideal gas at 0oC and 1 atm.

4) 4) V is directly proportional to nat constant P and T.5) 5) Some real gas volumes at STP are: O2-22.397 L; N2-

22.402 L; H-22.433L


16/22

E) We can solve a variety of problems with

the Ideal Gas Equation. 2

Q: Calculate the volume of 2.63 mol of O2

gas at 25oC and 0.986 atm pressure. Assume

O2behaves as an ideal gas under these

conditions.


17/22

E) We can solve a variety of problems

with the Ideal Gas Equation. 2

Calculate the volume of 2.63 mol of O2gas at 25oC and 0.986 atm pressure.

Assume O2behaves as an ideal gas

under these conditions.


18/22


What is partial pressure?


19/22


Suppose two or more non reacting gases are mixedtogether. Then what will be the pressure of thisgaseous mixture?

The pressure due to any individual gas in the gaseousmixture is known as the partial pressure of that gas.

The partial pressure of a gas in gaseous mixture is thepressure that the gas would exert if alone present inthe whole container.

Let us consider a vessel containing a mixture ofhydrogen and oxygen. If one gas is removed, then whatwill be the pressure of a gas alone?


20/22


In 1807 John Dalton, put forward the law to calculatethe total pressure of a gaseous mixture from the partialpressures of the component gases. This law is calledDaltons Law of partial pressure.

At constant temperature the total pressure exerted bya mixture of gases is equal to the sum of the partialpressures of the individual component gases.

If P1, P2, P3are partial pressures of constituent gases,

then the total pressure, Ptotalof the gaseous mixture isgiven by,

Ptotal=P1+P2+P3


21/22

Mathematical calculation of Daltons law

Let us consider a gaseous mixture composed of n1 moles of gas 1 and n2moles of gas 2 and n3 moles of gas 3. Let the total volume of the gaseousmixture be V and temperature be T Kelvin. If nt be the total moles of gaseousmixture then,

nt= n1+n2+n3(1)

Multiplying both sides of the equation (1) by RT/V, we get,

ntRT/V = n1RT/V +n2RT/V +n3RT/V..(2)But according to ideal gas equation ,We have,

PV =nRT or P =nRT/V

Therefore, pt= ntRT/V,

p1= n1RT/V

p2

= n2

RT/V

p3= n3RT/V

And from equation (2) using the following relationship,

Pt= p1+p2+p3.(3)

Where pt is the total pressure exerted by the gaseous mixture and p1, p2andP3 are the partial pressure of individual component gases 1 2 and 3

respectively. Equation (3) is the mathematical expression of Daltons law ofpartial pressure.


22/22

Thank you

Any Questions?

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