# Gaslawsstudyguide.2

June 2018

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## Transcript

Gas Laws Study Guide Notes: Properties of solids, liquids, & gases : Solids Particles very close o together Highest density o Lowest kinetic o energy Least amount of  o motion Definite shape & o volume Phase Changes Solid  liquid: melting Liquid  solid: freezing Liquids Particles loosely o held together Moderate density o Moderate kinetic o energy Some motion o Definite shape, no o definite volume o Gases Particles very far apart o o o motion o No definite shape or volume o gas  liquid: condensation liquid  gas: evaporating/vaporizing Least dense Most kinetic energy High amount of  No organization gas  solid: deposition solid  gas: sublimation Gases:  There are three main characteristics of gases – all of which are a result of the kinetic molecular theory which says: 1. all part partic icles les of a gas gas are are in const constant ant moti motion on 2. as a result of this this motion, motion, random collisi collisions ons occur, occur, but gases are not attracte attracted d or repelled from from each other 3. gases gases are much smaller smaller than than the distance distance betwee between n them.  The characteristics of gases are: 1. volume: volume: the amount amount of space space a gas occup occupies ies – usually usually measure measured d in liters liters or mL 2. Pressure: Pressure: forcer forcer per unit area area – comes comes from from particles particles banging banging into into the side side of the the containe container. r. Measured in kilopascals, atmospheres, or mm of mercury. 3. Temperatur Temperature: e: average average kinetic kinetic energy energy of the partic particles les of gas gas – measured measured in degrees degrees celciu celcius s or Kelvin. Kelvin. **ALWAYS HAS TO BE IN KELVIN FOR GAS LAW PROBLEMS** 4. STP: STP: standa standard rd temper temperatu ature re & pressu pressure re Pressure: 1 atm = 101.3 kPa = 760 mmHg (given on reference table) Temperature: 0 C = 273 K  K = C + 273 (given on reference 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 pressures of each part of the gas mixture. Dalton’s Law of Partial Pressure: Ptotal = P1 + P2 + P3 +… ° same, pressure & volume are indirectly proportional. proportional. If one 2. Boyle’s Law: if the temperature remains the same, condition goes up, the other goes down & vice versa. P1V1 = P2V2 temperature & volume are directly proportional. If  3. Charles’ Law: if the pressure remains constant, the temperature one condition goes up, so does the other. T1 V1 = V2 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. T1 P1 = P2 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/wants. 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 molK molK molK  **Be careful to make sure the units cancel!!! 6. 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 mass of the heavy gas & M 1 is the mass of the light gas 7. Gas Density: Rearranging the ideal gas law to find gas density so 8. Molar Mass: Rearranging the ideal gas law to find molar mass so 9. Relating partial pressure to mole fraction 10. Defining the RMS(root mean square) speed as a function of molar mass an temperature. This is the way to find the average speed of particle such as a molecule or element in a gas. 11. Van der Waals Equation: This is the better version of the ideal gas law but requires a chart that would have to be given to use. where  p is the pressure of the fluid V is the total volume of the container containing the fluid a is a measure of the attraction between the particles b is the volume excluded by a mole of particles n is the number of moles R is the universal gas constant, T is the absolute temperature 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? 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, N 2, CO2 or NH3 ? °