Chapter 11 - The Gas Laws courtesy of jOEl and AARon

A gas is a state of matter consisting of a collection of particles in random motion without a definite shape or volume. Gases expand to the size and shape of their containers, glide easily past each other similarly to water (note: both are considered fluids), have low densities (about 1/1000 of same substance in solid or liquid form), have volumes that can be greatly compressed, and will spread and mix with each other without being stirred.

States Of Gasses

Like matter, gases have many different states of existance:
  • Real Gas:A gas that does not behave completely according to the assumptions of The Kinetic-Molecular Theory*. idealgas.gif
  • Ideal Gas:A hypothetical gas that perfectly fits all of the assumptions of The Kinetic-Molecular Theory*.
  • Perfect Gas:A gas that follows the physical parameters of The General Gas Law.

*The Kinetic Molecular Theory:
  1. Gasses have many particles that are far apart, relative to their size
    • Most of the volume of a gas is empty space
    • Gasses have a lower density than other states of matter (It is compressed easily)
  2. Collisions between gas particles and between particles and container walls are elastic collisions (No net loss of kinetic energy)
  3. Kinetic energy is transferred during collisions
  4. Total kinetic energy remains constant as long as the temperature remain the same
  5. Gas particles are in continuous, random, rapid motion=kinetic energy
  6. The kinetic energy of particles overcomes attractive forces between them, EXCEPT when the temperature is where gas becomes liquid
  7. No forces of attraction occur between gas particles
  8. Temperature of the gas depends on the average kinetic energy


Gas Laws and Relationships

The following laws and relationships depict the effects of outside forces on gases, such as pressure, volume, etc
  • Note the variables:
P=Pressure
T=Temperature
V=Volume
N=Moles of a Substance
R=Ideal Gas Constant (0.082)
  1. Boyle's Law:This law relates pressure and volume, and the variables in this equation are inversely proportional (one increases as the other decreases and vice versa) The equation for this law is (P1)(V1)=(P2)(V2).boyle_pic.gif
  2. Charles's Law:This law relates volume and temperature, and the variables are directly proportional (both increase or decrease simultaneously). The equation for this law is V1/T1=V2/T2.
  3. Gay Lussac's Law:This law relates pressure and temperature, and the variables are directly proportional (both increase or decrease simultaneously). The equation for this law is P1/T1=P2/V2.
  4. The Combined Gas Law:This law groups the above listed into one conglomerate. It relates pressure, temperature, and volume. The equation for this law is (P1)(V1)/T1=(P2)(V2)/T2.
  5. Avogadro's Law:This law relates volume and the number of moles of the particular gas you are working with, and the variables in this situation are directly proportional. The equation for this law is V1/n1=V2/n2.
  6. Dalton's Law of Partial Pressures:This law is one that is easily utilized. It does not involve an equation, and is very simple. The law states that the total pressure of a system is equal to the sum of the partial pressures of the gases in that system. Basically, all that is required is basic addition: the total pressure is found by adding the pressures of the different gases.
  7. The Ideal Gas Law:This law relates pressure, volume, the number of moles, and temperature. This equation also uses a constant known as The Ideal Gas Constant, or 0.082. The equation for this law is PV=nRT

PRACTICE PROBLEMS

Answers can be found at this link: Answer Sheet


Question 1) In an experiment, 2.5 L of an unknown gas is placed under a pressure of 1 ATM. If the pressure is increased to 1.6 ATMs, what is the second volume of the gas?

Question 2) If a gas at 43 Degrees Celsius has a volume of 24.2 mL, what would the temperature be if the volume changes to 25.2 mL?
(dont forget to convert Degrees Celsius to Kelvin- *C+273)

Question 3) If at 273 K, a gas is at 1 ATM, what is the pressure at 315 K ?

Question 4) If a gas takes up 35 mL at 1 atm and 300K, assuming the pressure stays the same, what is the the volume if the gas is heated to 350K?


Question 5) If there are 2 mol of a gas in a 10 mL container, how many mol would fit in a 20 mL container?

Question 6) If there is a mixture of CO2 (g) and H2O (g) in a container that has a total pressure of 760 mmHg, and the CO2 has a pressure of 360 mmHg, what is the partial pressure of the H2O (g)?

Question 7) Using the Ideal gas law, What is the pressure of 3 mol of a gas that is in a 50 mL beaker at 273K?
(R= 0.082)


NOTE!!!! Helpful video below. takes a little while to load.



Quick Facts to remember**

  • Always, ALWAYS convert to Kelvin
  • Temperature is always on the bottom, and it is always a division

Works Cited

Most from the mouth of Mr P
Modern Chemistry Textbook
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