Gas Laws (Introduction and Abstract)

Experiment no. 8

: 07-07-14

Gas Laws Guillermo, Janina Suzette C. Escudero, Angela Julia R. De La Salle University – Dasmariñas Dasmariñas, Cavite Philippines

ABSTRACT

In this experiment on gas laws, we are to observe the behavior of gases and understand the principles of Combined Gas Law and Graham’s Law of Diffusion. There are two experiments: one focused on Combined Gas Law where an Erlenmeyer flask set-up is used where heating and cooling procedures are done to determine variables needed, such as temperature, volume, pressure and percentage difference; while on the other hand, Graham’s Law of Diffusion is demonstrated using a long glass tube where cottons dipped in Conc. HCl and Conc. NH4OH were placed on each end to be observed and be able to determine the diffusion rate as well as percentage difference. The pressure, volume, temperature, diffusion rates, ratios and percentage differences were calculated, obtained, and identified. All the methods used were effective in observing the behavior of gases and understanding the principles of the gas laws.

INTRODUCTION Ideal gas is a gas that obeys the ideal gas law, which is a combination of Avogadro’s Law and Combined Gas Law. The ideal gas law is approximately true for all gases under laboratory conditions such as room temperature and one atmosphere pressure. Since the molecules of real gases move independently and interact weakly with one another, they behave nearly ideally under normal conditions. The equation of ideal gas is expressed mathematically as: Pv = nRT Where: P = pressure .

V = volume

n = number of moles

T = temperature

R = gas constant (~ 0.0821 L atm / K mol)

Before the ideal gas was formulated, scientists worked on how the volume of gases was affected by pressure, temperature, number of mole of gas. Example of which is Boyle’s Law, which relates volumes of gas to its temperature; where here it is seen that volume inversely proportional to the pressure and is mathematically expressed as: PV = a constant

or

P1V1= P2V2

For a fixed volume of gas at a constant pressure, volume is directly proportional to the temperature in kelvins (K), it is the Charles’ Law:

a constant =

K= °C +273

V T

or

V 1 V2 = T1 T 2

And Gay-Lussac’s Law for a fixed mass of gas at a constant volume, the pressure is directly proportional to the temperature in kelvins (K), expressed as:

a constant =

P T

P1 P2 = T1 T2

Or

When Boyle’s, Charles’ and Gay-Lussac’s Laws are combined they form the Combined Gas Law, expressed as:

a constant =

PV T

Or

P 1 V 1 P2 V 2 = T1 T2

Similarly, Avogadro’s Law relates the volume of gas to its number of moles. It states that under the same temperature and pressure, the volume of gas is directly proportional to its number of moles, which can be expressed as:

V 1 n 2=V 2 n 1

n= moles of gas (mol)

REFERENCES (1) Samonte J.L, Figueroa L.V General Chemistry Laboratory Manual 4 th Edition, C&E Publishing Inc., 2014. (2) Bettelheim F. A, Brown W.H, Campbell M.K, Farrell S.O, Introduction to General, Organic and Biochemistry, 9th Edition, Cengage Learning Inc., 2010.