2 Behavior of GasesGases behave much differently than liquids and solids and thus, have different laws.Because gas molecules have no forces keeping them together, they fill whatever container in which they are kept.This distance between the molecules also means they can be compressed.
3 Kinetic Molecular Theory of Gases Model explaining gas behavior.1) A gas consists of small particles (atoms or molecules) that move randomly with high velocities.2) The attractive forces between gases can be ignored.
4 Kinetic Molecular Theory of Gases 3) The actual volume that the gas molecules occupy is usually much smaller than the volume of the container. - Therefore, gases can be easily compressed because of all the empty space. 4) The average kinetic energy (temperature) of gas molecules is proportional to the Kelvin temperature.
5 Kinetic Molecular Theory of Gases 5) Gas particles are in constant motion, moving rapidly in straight paths until collide with another gas molecule and change direction. - When they hit each other or the walls of the container, they create gas pressure. - As collisions increase, pressure increases.
6 Properties of GasesThe following properties are used to describe gases:PressureVolumeTemperatureAmount of gas
7 Pressure of a GasPressure of a gas occurs when gas molecules strike each other as well as the sides of a container.As collisions increase between molecules, pressure increases.The pressure of the air molecules around us is called atmospheric pressure.
8 Atmospheric pressure – decreases with altitude because there are fewer air molecules present
9 Common Units of Pressure Atmosphere (atm)Millimeters of Mercury (mmHg)Torr (torr)Pounds per square inch (lb/in2 )Pascal (Pa)
10 Barometric Pressure -As air pressure increases (downward) the barometer reading (Hg) rises upward.
11 Volume of a GasThe volume of a gas equals the size of the container in which the gas is placed.Volume of gases are generally measured in liters (L) or cubic decimeters (dm3 ) which equal the same amount.Also, 1mL = 1 cm3
12 Temperature of a GasTemperature reflects the average kinetic energy due to the movement of a gas.Measured in Kelvin (K)
13 Amount of a GasUses moles to describe the relative quantity of molecules of a gas that are present.
14 What happens to the pressure of a gas when volume decreases? Pressure decreasesPressure increasesNo changeUnable to tell
15 What is the relationship between pressure and volume? DirectInverseExponentialNo relationship
16 Boyle’s LawBoyle’s Law – If temperature is held constant, gas pressure is inversely proportional to the volume of the gas.Boyle’s Law: P1 V1 = P2 V2
17 What happens to the volume of a gas when temperature increases? Volume decreasesVolume increasesNo changeUnable to tell
18 What is the relationship between temperature and volume? DirectInverseExponentialNo relationship
19 Charles’ LawAs temperature increases, average kinetic energy of gas molecules increases.As the molecules move faster, volume increases.Charles’ Law – If pressure is held constant, there is a direct relationship between volume and temperature.
20 Charles’ Law V1 = V2 T1 T2 Note: Temperature is measure in Kelvin Kelvin = Celsius + 273
21 What happens to the pressure of a gas when temperature increases? Pressure decreasesPressure increasesNo changeUnable to tell
22 What is the relationship between temperature and pressure? DirectInverseExponentialNo relationship
23 Gay – Lussac’s LawAs temperature increases, collisions increase and pressure increases as well.Gay – Lussac’s Law – If volume is held constant, there is a direct relationship between pressure and temperature.
24 Gay – Lussac’s Law P1 = P2 T1 T2 Gay-Lussac’s Law is true if number of moles of the gas as well as the volume is held constant.Note: Temperature is measure in KelvinKelvin = Celsius + 273
25 Combined Gas Law P1 V1 = P2 V2 T1 T2 The combined gas law applies as long as the number of moles of a gas are held constant.Note: Temperature is measure in KelvinKelvin = Celsius + 273
26 What happens to the volume of a gas when the number of atoms increases? Volume decreasesVolume increasesNo changeUnable to tell
27 What is the relationship between volume and moles of a gas? DirectInverseExponentialNo relationship
28 Avogadro’s LawV1 = V2n n2Avogadro’s Law is true if pressure and temperature are held constant.Note: n = moles of the gas
29 Avogadro’s LawV1 = V2n n2The combined gas law applies as long as the number of moles of a gas are held constant.Note: Temperature is measure in KelvinKelvin = Celsius + 273
30 STP STP – Standard Temperature and Pressure STP: T = 273K (or 0o C) P = 1 atm or 760 mmHg
31 Molar Volume***** At STP, according to Avogadro, any gas has a molar volume of 22.4L.Conversion factor: 1 mole (of any gas) = 22.4L
32 Law of Partial Pressures The Law of Partial Pressures states that the total pressure of a gas is equal to the sum of all of the individual pressures.Ptot = P1 + P2 + … Pn
33 True or False: Increasing the volume of a gas increases the pressure.
34 True or False: Increasing the pressure of a gas increases the temperature.
35 True or False: 1 mole of iron metal has a volume of 22.4L at STP.
36 True or False: Decreasing the temperature of a gas increases the pressure.
37 True or False: Decreasing the temperature of a gas increases the volume.
38 True or False: Increasing the moles of a gas increases the pressure.
39 Ideal Gas LawThe four properties of gases (temperature, pressure, volume, and amount) can be combined to give the Ideal Gas LawPV = nRT***Use the ideal gas law when you know 3 out of the 4 properties of a given gas.
40 PV = nRTR is a constant. To calculate R, put all other variables at STP and solve for R.P = 1 atm or 760 mmHgT = 273KN = 1 moleV = 22.4LR = if P is in atm; 62.4 if P is in mmHg