Combined Gas Law Avogadro’s Law
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Combined Gas Law Avogadro’s Law Write out the notes that are not in italics!
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Combined Gas Law Avogadro’s Law. Write out the notes that are not in italics!. The Combined Gas Law. The gas laws may be combined into a single law, called the combined gas law , that relates two sets of conditions of pressure, volume, and temperature by the following equation. - PowerPoint PPT Presentation
Transcript of Combined Gas Law Avogadro’s Law
Combined Gas LawAvogadro’s Law
Write out the notes that are not in italics!
The Combined Gas Law
• The gas laws may be combined into a single law, called the combined gas law, that relates two sets of conditions of pressure, volume, and temperature by the following equation.
• With this equation, you can find the value of any one of the variables if you know the other five.
Applying the Combined Gas Law• A sample of nitrogen monoxide has a volume
of 72.6 mL at a temperature of 16°C and a pressure of 104.1 kPa.
• What volume will the sample occupy at 24°C and 99.3 kPa?
• Start by converting the temperatures to kelvins.
Applying the Combined Gas Law
• Next, solve the combined gas law equation for the quantity to be determined, the new volume, V2.
Applying the Combined Gas Law
• Substitute the known quantities and compute V2.
=(104.1 kPa)(72.6mL)(297K)
(99.3 kPa)(289K)
= 78.2mL
STP• At times a problem may say a
substance is at STP or standard temperature and pressure.
• Standard temperature is 0°C• Standard pressure is 1atm• When a problem occurs at STP, you
can put in the standard temp and pressure.
Avogadro’s Principle • In the early nineteenth century, Avogadro
proposed the idea that equal volumes of all gases at the same conditions of temperature and pressure contain the same number of particles.
• An extension of Avogadro’s principle is that one mole (6.02 x 1023 particles) of any gas at standard temperature and pressure (0°C and 1.00 atm pressure, STP) occupies a volume of 22.4 L.
Avogadro’s Law
• Avogadro’s Law This law relates volume with the number of
moles of a substance.
V1
n1
V2
n2
=
Practice avogadro’s law
• A 3.2mol sample of Helium is at 1.0atm. What is the pressure if the sample is increased to 7.6moles?
First solve the equation for P2
P2 =P1 n2
n1
Then plug in the numbers: P2 =(1.0atm)
(3.2mol)
(7.6mol)
P2 = 2.4atm
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The Ideal Gas Law
• The pressure, volume, temperature, and number of moles of gas can be related in a simpler, more convenient way by using the ideal gas law.
• The following is the law’s mathematical expression, where n represents the number of moles.
PV = nRT
The Ideal Gas Law
• The ideal gas constant, R, already contains the molar volume of a gas at STP along with the standard temperature and pressure conditions.
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The Ideal Gas Law
• The constant R does the job of correcting conditions to STP.
• You do not have to correct STP in a separate step.
The Ideal Gas Law
• The Value of R depends on the units in which the pressure of the gas is measured, as shown below.
• These values are all equivalent. Use the one that matches the pressure units you are using.
Applying the Ideal Gas Law
• What pressure in atmospheres will 18.6 mol of methane exert when it is compressed in a 12.00-L tank at a temperature of 45°C?
• As always, change the temperature to kelvins before doing anything else.
Applying the Ideal Gas Law
• Next solve the ideal gas law equation for P.
• Substitute the known quantities and calculate P.
P =(18.6mol)(0.0821Latm/molK)(318K)
(12.00L)
P = 40.5 atm
