 We are still using the idea of the kinetic- molecular theory. All particles are in motion › We are still relating this to ideal gases!!!!  This affects… › Pressure › Volume

 Pressure (P)- is defined as the force per unit area on a surface  Tire pressure- › When you have a flat tire, you either air it up or call someone to air it up. › When air is inserted into the tire, more air particles, more collisions, more pressure.

 Pressure= Force/Area › Unit of force is a newton (N)  Force= mass * acceleration (remember the f=ma weird videos from 8 th grade) › Unit of area  Unit of length 2

 The atmosphere exerts pressure on the Earth due to all the gases. › Atmospheric pressure › Pressure is lower at higher altitudes  Changes of altitudes (pressure) causes your ears pop when you go up and down hills, taking off or landing an airplane.

 Barometer-a device to measure atmospheric pressure  Developed by Torricelli in the early 1600’s  Units of pressure › mm Hg (millimeter of mercury) › atm (atmosphere of pressure) › Pa (pascal) › psi (pounds per square inch) *** only in America

 1 torr = 1mm Hg  1 atm = 760 mm Hg  1 atm = 760 torr  1 atm = x 10 5 Pa  1 atm = kPa  1atm = psi  1 psi = x 10 3 Pa

 Covert a pressure of 1.75 atm to kPa and to mm Hg.  The critical pressure of carbon dioxide is 72.2 atm. What is this value in units of Pascal's?

 The sum of the partial pressures of a mixture of gases is the total pressure exerted by the enclosed gases.  P total = P gas 1 + P gas 2 + ….  If the pressure of air in this room is 100 kPa and nitrogen represents 80% and oxygen 20%, what is the pressure of each gas?

 Some hydrogen gas is collected over water at 20 o C. The levels of water inside and outside the gas-collection bottle are the same. The partial pressure of hydrogen is torr. What is the barometric pressure at the time the gas is collected?

 Robert Boyle was the first person to collect a gas for study and analysis.  The volume of a gas in an enclosed container varies inversely as the pressure, IF the temperature remains constant.  V 1 P 1 = V 2 P 2

 The volume of a balloon is 454 cm 3 at 1.25 atm. What is the volume if the pressure decreases to 0.95 atm?

 A balloon filled with helium gas has a volume of 500 mL at a pressure of 1 atm. The balloon is released and reaches an altitude of 6.5 km, where the pressure is 0.5 atm. If the temperature has remained the same, what volume does the gas occupy at this height?

 uixZoVuc

 French scientist Jacques Charles-1787  The volume of a gas varies directly as the Kelvin temperature, IF the pressure remains constant.  K= o C **We will use 273  V 1 = V 2 T 1 T 2

 What volume will a sample of nitrogen occupy at 28.0 o C if the gas occupies a volume of 457 cm 3 at a temperature of 0.0 o C at constant pressure?

 A sample of neon gas has a volume of 752 mL at 25.0 o C. What will the volume at 100 o C be if pressure is constant?

 Coke Can demo

 Joseph Bay-Lussac in 1802  The pressure of a gas varies directly with the Kelvin temperature IF the volume remains constant.  P 1 = P 2 T 1 T 2

 What happens to tire pressure on cold days?

 The pressure in a container is 700 mmHg at 25 o C. What is the pressure when the temperature reaches 100 o C?

 P 1 V 1 = P 2 V 2 T 1 T 2 The temperatures MUST be in Kelvin. The pressures and volumes must be in the same units of measure on both sides.

 A 150 mL container is filled with hydrogen at 15.0 o C and exerts a pressure of kPa. What will the volume of the gas occupy at 40.0 o C and 94.5 kPa?

 The volume of a gas is 27.5 mL at 22.0 o C and atm. What will the volume be at 15.0 o C and atm?

 If the problem indicates constant pressure, ignore P 1 and P 2 (Charles’s law)  If the problem indicates constant volume, ignore V 1 and V 2 (Gay-Lussac’s law)  If the problem indicates constant temperature, ignore T 1 and T 2 (Boyle’s law)

 What is the temperature of the air in a tire if the pressure doubles from 1.5 atm to 3.0 atm if the original temperature was 35 o C? Assume the tire has a constant volume.

 Gases are commonly collected by bubbling through water.  The water vapor molecules will exert a pressure, which will affect the pressure of the dry gas.  P total = P gas + P water vapor  Therefore, a correction must be made P dry gas = P total – P water vapor (from the table)

 A gas is collected over water at 30 o C at a pressure of 745 torr (mmHg). What is the pressure of the dry gas?  A gas is collected by water displacement at 45 o C at 122 kPa. What is the pressure of the dry gas?  A gas is collected over water at 23 o C at a pressure of 1.6 atm. What is the pressure of the dry gas?

 What is the volume of dry hydrogen at STP if 45 mL was collected by water displacement at 55 o C and 98 kPa?

 Five hundred liters of oxygen was collected over water at 20.0 o C and 800 mmHg. What will the volume of the dry gas be at 30.0 o C and 1200 mmHg?

 We can use the coeffiecents of balanced equations to compare › Volume and molecules  We also have what we call standard molar volume of a gas… › STP (standard temperature and pressure) › At 1 atmosphere of pressure, 273 K, then we will have 22.4L of 1 mole of gas.

 At STP, what is the volume of 7.08 moles of nitrogen gas?  A sample of hydrogen gas occupies 14.1 STP. How many moles of the gas are present.  Assuming all volume measurements are made at the same temperature and pressure, what volume of hydrogen gas is needed to react completely with 4.55 L of oxygen gas to produce water vapor?

 The mathematical relationship amount pressure, volume, temperature, and the number of moles of a gas. › PV=nRT › P=pressure › V=volume in L except when dealing with Pa › n= number of moles › R= ideal gas constant › T= temperature in Kelvins

 Ideal Gas Constant, R, Values › 62.4 when using mm Hg › when using atm › when using Pa › when using kPa

 What pressure, in atmospheres, is exerted by mole of hydrogen gas in a 4.08 container at 35 o C?  A gas sample occupies 8.77 L at 20 o C. What is the pressure, in atmospheres, given that there are 1.45 moles of gas in the sample?

 The relative rate at which two gases at the same temperature and pressure will effuse (pass through a small opening; ie. tire,balloon, etc) varies as the square root of the ratio of the molecular masses of the gases.  Rate A / Rate B = sqrt (mass B / mass A)

 Quick lab on page 387

 What is the ratio of helium balloon effusion to nitrogen (air) if they are at the same temperature and pressure?