Thermodynamics: Ideal Gas Law

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This text is meant to accompany class discussions. It is not everything there is to know about the basics of torque and the two conditions of equilibrium. It is meant as a prep for class. More detailed notes and examples are given in the class notes, presentations, and demonstrations (click here.)

Click for the questions that go with this reading

Ideal Gas Law

An ideal gas is one that meets the following characteristics.

The gas is made up of a simple monotomic molecules.
The space between molecules is larger than the molecules.
Molecules collide elastically with not loss of energy.
No long range forces act between molecules.

There are several laws that describe the behavior gases.

Other Gas Laws

When combined, these laws lead to the Ideal gas law. The ideal gas law can be described by the equation below.

PV = nRT's Variables

If you have 12 donuts you would say "...you have a dozen donuts. If you have 602,200,000,000,000,000,000,000 donuts you would say. "...you hade a mole of donuts." That's enough donuts to give everyone on the planet about a trillion donuts. It is very big number. in sceince we used alower case "n" to represent a mol of molecules.

Notes about the variables and formula.

	The truth about "PV." Look at the units of pressure and volume. When the force is parallel to the displacement, the units of N•m are defined as a Joule. What you will see later is that pressure time volume do indicate the energy of the gas as measured in Joules.
	There are several values for the ideal gas law constant, "R." Choose the value that matches the pressure and volume's units.
	Because PV represents energy, the temperature scale that is used must also relate to energy. That's why Kelvins are used. Celsius can only be used when you adjust the formula to look for a " ΔT " instead of " T ".

Example 1

Question
Solution
Video Solution

How many moles of an ideal gas are in a container with a volume of 10.0 liters, that was sealed at sea level where the temperature is 31.0 degrees Celsius?

Omit

Example 2

Question
Solution
Video Solution

A syringe has a ruber stopped attached to the needle in such a way that air cannot escape the syringe. By what factor would the pressure inside the syringe change by if the volume was slowly reduced to 1/3 of the original volume?

A syringe has a ruber stopped attached to the needle in such a way that air cannot escape the syringe. By what factor would the pressure inside the syringe change by if the volume was slowly reduced to 1/3 of the original volume?

Solution

Because the syringe is sealed the number of molecules ramains unchanged. By moving slowly the temperature is held constant.

PV=nRT

Since nRT is held constant, pressure and volume are inversely proportional to each other. Therefore, if the volume decreases by a factor of 3 then the pressure increases by a factor fo 3.

Omit

by Tony Wayne ...(If you are a teacher, please feel free to use these resources in your teaching.)

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