1 Chapter 5: GASES

2  In this chapter we will:  Define units of pressure and volume  Explore the properties of gases  Relate how the pressure, volume, and temperature of gases are related

3 Characteristics of Gases  Uniformly fills any container.  Are highly compressible  Mixes completely with any other gas  Exert pressure on its surroundings.

4 Pressure ] Pressure is the force acting on an object per unit area: P = F/A ] Gravity exerts a pressure on the earth’s atmosphere

5 Pressure ] The pressure of a 1 m 2 column of air on earth exerts a pressure of about 100 kPa

6 Units of Pressure  SI units = Newton/meter 2 = 1 Pascal (Pa)  101,325 Pa = kPa = 1 atmosphere = 1 atm  1 atm = 760 mm Hg = 760 torr

7 Pressure Atmospheric Pressure and the Barometer  Atmospheric pressure is measured with a barometer.  Standard atmospheric pressure is the pressure required to support 760 mm of Hg in a column

8 Units of Pressure The manometer above is another tool used to measure pressure. How would you measure how much pressure is being exerted on the column of mercury?

9 Gas Laws: Boyle’s Law  The volume of a fixed quantity of gas is inversely proportional to its pressure  Pressure  Volume = Constant (T = constant)  P 1 V 1 = P 2 V 2 (T = constant)  V  1/P (T = constant)

10 Gas Laws: Boyle’s Law

11 Gas Laws: Charles’s Law  The volume of a gas is directly proportional to temperature  V = constant T (P = constant)  V/T = constant

12 Gas Laws: Charles’s Law The plot of V vs. T is a straight line. What does that tell us about the relationship between V and T?

13 Gay-Lussac’s Law Gas Laws: Gay-Lussac’s Law Gay-Lussac’s Law of Combining Volumes: at a given T and P the volume of gases which react are small whole number ratios.

14 Gas Laws: Avogadro’s Law  For a gas at constant temperature and pressure, the volume is directly proportional to the number of moles of gas V = constant n n = number of moles of gas  22.4 L of any gas at 0° C contains 6.02x10 23 gas molecules

15 The Meaning of Temperature  Temperature measures the average kinetic energy of atoms (higher T means greater motion.)  We use the Kelvin temperature scale as an index of the random motions of gas particles.

16 Standard Temperature and Pressure “STP”  P = 1 atm  T = 0  C = 273 K  The molar volume of an ideal gas is liters at STP

17 The Ideal Gas Law  An equation of state for a gas.  “state” is the condition of the gas at a given time. PV = nRT R = Ideal Gas constant = L atm   mol  P = pressure in atm V = volume in liters n = moles T = temperature in Kelvins

18 The Ideal Gas Law Sample Exercise: A sample of H 2 has a volume of 8.56 L at a temperature of 0° C and a pressure of 1.5 atm. Calculate the moles of H 2 molecules present in this gas sample.

19 The Ideal Gas Law Sample Exercise 2: A sample of gas contains 0.35 mol of argon gas at a temperature of 13°C and a pressure of 568 torr is heated to 56°C and a pressure of 897 torr. Calculate the change in volume that occurs.