Chapter 10; Gases

Elements that exist as gases at 250C and 1 atmosphere

Physical Characteristics of Gases Gases assume the volume and shape of their containers. Gases are the most compressible state of matter. Gases will mix evenly and completely when confined to the same container. Gases have much lower densities than liquids and solids.

Gas Laws In the first part of this chapter we will examine the quantitative relationships, or empirical laws, governing gases. First, however, we need to understand the concept of pressure. 2

Pressure P = Force/unit area Force exerted per unit area of surface by molecules in motion. P = Force/unit area 1 atmosphere = 14.7 psi 1 atmosphere = 760 mm Hg 1 atmosphere = 101,325 Pascals 1 Pascal = 1 kg/m.s2 2

Barometer Force Area Pressure = Units of Pressure 1 pascal (Pa) = 1 N/m2 1 atm = 760 mmHg = 760 torr 1 atm = 101,325 Pa

The Empirical Gas Laws V a 1/P (constant moles and T) or Boyle’s Law: The volume of a sample of gas at a given temperature varies inversely with the applied pressure. V a 1/P (constant moles and T) or 3

Boyle’s Law P a 1/V Constant temperature Constant amount of gas P x V = constant P1 x V1 = P2 x V2

A Problem to Consider A sample of chlorine gas has a volume of 1.8 L at 1.0 atm. If the pressure increases to 4.0 atm (at constant temperature), what would be the new volume? 7

A sample of chlorine gas occupies a volume of 946 mL at a pressure of 726 mmHg. What is the pressure of the gas (in mmHg) if the volume is reduced at constant temperature to 154 mL? P1 x V1 = P2 x V2

As T increases V increases

The Empirical Gas Laws V a Tabs (constant moles and P) or Charles’s Law: The volume occupied by any sample of gas at constant pressure is directly proportional to its absolute temperature. V a Tabs (constant moles and P) or 3

Variation of gas volume with temperature at constant pressure. Charles’ Law V a T Temperature must be in Kelvin V = constant x T V1/T1 = V2/T2 T (K) = t (0C) + 273.15