Gas Law
Boyle’s Law
P1V1=P2V2
Charles’s Law
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Combined Gas Law
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Dalton’s Law
P to 1=P1+P2+P3+…….
Volume, temperature, pressure and number of moles are interrelated in gaseous system.
https://phet.colorado.edu/en/simulation/legacy/gas-properties
Click on the above simulation and observe the properties of Gas.
Boyle’s law: Volume of a fixed amount of gas is inversely proportional to the pressure applied to the gas if the Temp is kept constant.
Boyle’s law has wide application in various fields like scuba diving, human breathing technique. When a person breathe in, the diaphragm contracts and volume of the lungs get bigger and pressure is low inside the body than outside pressure. Since outside pressure is high, air goes inside the body. When we breathe out, the diaphragm relaxes, volume decreases, high pressure gas comes out of the body.
Mathematically we can write,
at constant T
P1= initial pressure, P2= final pressure, T1= initial temp in Kelvin, T2= final temp in Kelvin
If we plot different Pressure vs. Volume for a gaseous system at a constant temperature, the curve will be parabolic in nature.
Example: A 4.0 L container of Helium gas has a pressure of 15.0 atm. What pressure does the gas exert if the volume is increased to 8.0 L?
Ans: since the volume is doubled, pressure must be half of the initial pressure.
New pressure= 15.0/2= 7.50 atm
Charles’s law: Volume of a fixed amount of gas is directly proportional to the kelvin temp if the pressure is kept constant.
This concept is applied in hot air balloon, where the volume of the gas is expanded by applying heat and once it becomes less dense than air, it can float in air.
Mathematically we can write:
at constant P
V1= initial pressure, V2= final pressure, T1= initial temp in Kelvin, T2= final temp in Kelvin
We can understand the absolute zero temperature from Charles’s law. For a sample of gas, when temperature is decreases, volume of the gas molecules decrease. According to the kinetic Molecular theory, the energy of the gas molecules is directly proportional to the kelvin temp. So gas molecules will move slowly as the temperature decreases. Therefore, hypothetically if the absolute temperature of a gaseous system reaches zero i.e. -2730C, all the gas molecules motion will be ceased and the volume of the gas molecule would be zero. In reality, experiments done at lower temp that show the volume decreases steadily but so far, zero volume hasn’t reached.
Example: A volume of 1.00L of gas at 370C is expelled from the lungs to cold outside at temperature -50C. What is the volume of the air at that temperature?
Ans: V2 is unknown.
1.00/(37+ 273) = V2/( -5+ 273) , 1/310=V2/268 or V2= 0.865 L
Avogadro’s law: Volume of a of gas is directly proportional to the number of moles of gas if the pressure and Temp are kept constant.
V1= initial volume v2= final volume, n1= initial moles n2= final moles
Example: The lungs of an average male holds 0.25 mol of air in a volume of 5.5 L. How many mole sof air do the lungs of an average female hold if the volume is 4.5 L?
Ans: n2 is unknown.
5.5/0.25= 4.5/n2, 22= 4.5/n2 or n2= 0.205 mol or 0.20 mols
P1= initial pressure, P2= final pressure, T1= initial temp, T2= final temp
Gay Lusaac’s law can also be observed the above diagram, where application of heat to a gaseous system increases the pressure of the gas.
Example: The tire on a bicycle in a cool garage is stored at 200C and 80. Psi. What is the pressure inside the tire after riding the bike at 430C?
Ans: P2 is unknown, 80/(20+273)= P2/(43+ 273)
0.273= P2/316 or P2= 0.273*316= 86.3 psi or 86 psi.
The following activity has been taken from AACT ( American association of chemical teachers)
https://teachchemistry.org/periodical/issues/november-2015/gas-laws
In this investigation you will examine three gas laws including Boyle’s Law, Charles’ Law and Gay-Lussac’s Law. You will explore how manipulating the variables of volume (L), pressure (atm) and temperature (K) can affect a sample of gas. The formula for each of the gas laws are:
Boyle’s Law | Charles’s law | Gay Lussaac’s Law | |||
P1V1= P2V2 | V1/T1= V2/T2 | P1/T1= P2/T2 |
Prelab Questions
332 267
295 x
Procedure
Visit http://www.teachchemistry.org/gaslaws. Make sure that you select the “Boyle’s Law” tab to begin; it will be shown in white. You should see the picture below on your screen.
Boyle’s Law
a. Observations when Volume is reduced: | b. Calculation |
P1V1 = P2V2 |
Using the pressure control arrows, reduce the pressure of the gas to 0.700atm.
a. Observations when Pressure is reduced: | b. Calculation |
P1V1 = P2V2 |
P1 = 1.00atm | P2 = 1.50atm | P3 = 2.00atm | P4 = 2.50atm | P5 = 2.90atm |
V1 = | V2 = | V3 = | V4 = | V5 = |
Important Terms
Direct relationship: A relationship between two variables, where a change in one variable results in the same change in the other variable. For example, if one variable is increased, then the other variable will also increase.
Indirect relationship: A relationship between two variables, where a change in one variable results in the opposite change in the other variable. For example, if one variable is increased, then the other variable will decrease.
Charles’ Law
Change the simulation to “Charles’ Law” by clicking the tab at the top of the screen it will be shown in white. You should see the picture below on your screen.
V1 = V2
T1 T2
Using the volume control arrows, reduce the volume of the gas to 1.86L.
a. Observations when Volume is reduced: | b. Calculation |
V1 = V2T1 T2 |
Volume (L)
Temperature (K)
Gay-Lussac’s Law
Change the simulation to “Gay-Lussac’s Law” by clicking the tab at the top of the screen it will be shown in white. You should see the picture below on your screen.
fill in the corresponding T2 value in the data table below.
P1 = 1.00atm | P2 = 1.50atm | P3 = 2.00atm | P4 = 2.50atm | P5 = 2.90atm |
T1 = | T2 = | T3 = | T4 = | T5 = |
Using the temperature control arrows, reduce the temperature of the gas to 158K.
a. Observations when Volume is reduced: | b. Calculation |
P1 = P2T1 T2 |
Checking Comprehension
Please create a list of the variable given in each problem and show all your work required to complete the calculation.
Boyle’s Law
P1V1=P2V2
Charles’s Law
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= |
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Combined Gas Law
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= |
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Dalton’s Law
P to 1=P1+P2+P3+…….
At constant temperature volume of a gas is inverse by proportional to the pressure applied to it.
Product of pressure and volume of a fixed amount of gas is directly proportional to the kelvin temp
Connect pressure, volume, temp and molar amount of a gas under one set of conditions. If three of the four variables are known, fourth one can be calculated.
total pressure exerted by a mixture of gases is equal to the sum of the partial pr. of individual gases.
Temp, moles
Pressure, moles
Number of moles
R= .0821 L-atm/motk
Pressure, volume
Volumes, temp
Pressure , temp, volume
Pressure, volume, moles , temp