# Gas Laws Study Guide - DOC - DOC

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```					Unit 10: Gas Laws Study Guide

Notes:
Properties of solids, liquids, & gases: Recall from earlier in the course!!

Solids                                   Liquids                          Gases
o   Particles very close                 o   Particles loosely held        o Particles very far apart
together                                 together                      o Least dense
o   Highest density                      o   Moderate density              o Most kinetic energy
o   Lowest kinetic energy                o   Moderate kinetic energy       o High amount of motion
o   Least amount of motion               o   Some motion                   o No definite shape or
o   Definite shape & volume              o   Definite shape, no definite      volume
volume                        o No organization

Gases:
There are three main characteristics of gases – according to the kinetic molecular theory which says:
1. Gas particles are small, hard, spheres (remember John Dalton!!)
2. All particles of a gas are in constant, straight line, motion
3. As a result of this motion, random, elastic collisions occur
4. Gases are not attracted to each other or the container
5. Gases have virtually no volume as they are much smaller than the distance between them.
6. The average kinetic energy of a collection of gas particles is dependent on the temperature only
The characteristics of gases are:
1. volume: the amount of space a gas occupies – usually measured in liters or mL
2. Pressure: forcer per unit area – comes from particles banging into the side of the container.
Measured in kilopascals, atmospheres, or mm Hg.
3. Temperature: average kinetic energy of the particles of gas – measured in degrees celsius or Kelvin.
**ALWAYS HAS TO BE IN KELVIN FOR GAS LAW PROBLEMS**
4. STP: standard temperature & pressure
Pressure: 1 atm = 101.3 kPa = 760 mmHg            (given on reference table)
Temperature: 0C = 273 K                         K = C + 273 (given on reference table)
Volume: 1 mole = 22.4 L
Scientific Laws & Discoveries:
1. Dalton said that the total pressure of a gas is equal to the sum of the pressures of each part of the gas
mixture. Dalton’s Law of Partial Pressure: Ptotal = P1 + P2 + P3 +…

2. Boyle’s Law: if the temperature remains the same, pressure & volume are inversely (indirectly) proportional.
If one condition goes up, the other goes down & vice versa.      P1V1 = P2V2
(what does the graph look like?)

3. Charles’ Law: if the pressure remains constant, the temperature & volume are directly proportional. If one
condition goes up, so does the other.                   V1 = V2
(what does the graph look like?)                         T1     T2

4. Gay Lussac’s Law: if the volume remains constant, the pressure & temperature are directly proportional – if
one condition goes up, so does the other.              P1 = P2
(what does the graph look like?)                        T1     T2

5. Combined Gas Law: shows the previous 3 gas laws in one. Only one found on the reference table. To use
any of the 3 previous laws, simply eliminate the variable that remains constant.
P1V1 = P2V2
T1      T2
6. Ideal Gas Law: Avogadro came along & said that perhaps the number of particles (atoms or molecules) in
the gas sample may affect the three characteristics of gases. He was right. So, the number of moles (n) in
the sample also has an effect. May have to convert from grams to moles or vice versa depending on what
the question gives/asks for.   PV = nRT
R is the gas law constant (there are 3 different ones you can used based on the unit the pressure is given
in). All of these constants are given on the reference table.
R=      0.0821 Latm =           8.31 LkPa          =     62.4 LmmHg
moleK                moleK                    moleK
**Be careful to make sure the units cancel!!!**
7. Graham’s Law: Heavier gases travel slower than lighter gases (look at the molar masses to determine which
is heavier). You can determine how much faster using the following equation:
√M2 / √M1 where M2 is the molar mass of the heavy gas & M1 is the molar mass of the light gas

Practice Problems:
1. A gas mixture at STP includes nitrogen (0.781 atm), carbon dioxide (0.001 atm) argon (0.009 atm) &
oxygen. According to Dalton’s Law, what is the partial pressure of oxygen in atm if the total pressure is
at STP (1 atm). What is the pressure in mmHg?

2. A mixture of a gas contains 50.0 kPa of chlorine, 22.3 kPa of He, & 43.7 kPa of bromine. What is the total
pressure of this deadly mixture? Is this at STP?

3. The pressure of 3.5 L of nitrous oxide anesthetic gas is changed from 760 mmHg to 364 mmHg. Assuming
the temperature remains constant, what will the resulting volume be?

4. If a sample of He gas occupies 12.1 L at 332 C, what will be its new volume at 47C, if the pressure
remains constant?

5. If a sample of carbon dioxide occupies 5.2 L at 80C & at 200 kPa, what will be its volume at STP?

6. Calculate the number of liters occupied at STP by 6.8 moles of Kr.

7. How many moles of fluorine gas occupy 8.2 L at a temperature of 350K with a pressure of 1.5 atm?

8. What pressure will be exerted by 1.45 moles of hydrogen gas at 25C if the volume is 2.5 mL?

9. What gas can travel faster – carbon dioxide or fluorine? How much faster will it travel? Try this!!

10. What is the pressure of 15 L of gas that was originally 75C & 250 kPa & was changed to 50C & 2.1L?

11. Which of the following behaves most like an ideal gas: He, N2, CO2 or NH3 ?

12. What are the conditions of temperature and pressure that result in REAL gases behaving most like IDEAL