RI 2022 The Gaseous State v2.0

Content Raffles Institution Year 5 H2 Chemistry 2022 Lecture Notes 4 - The Gaseous State • Ideal gas behaviour and deviations from it • pV = nRT and its use in determining a value for Mr • Dalton's Law and its use in determining the partial pressures of gases in a mixture Learning Outcomes Candidates should be able to: (a) state the basic assumptions of the kinetic theory as applied to an ideal gas (b) explain qualitatively in terms of intermolecular forces and molecular size: (i) the conditions necessary for a gas to approach ideal behaviour (ii) the limitations of ideality at very high pressures and very low temperatures (c) state and use the general gas equation pV = nRT in calculations, including the determination of Mr (d) use Dalton's Law to determine the partial pressures of gases in a mixture Lecture Outline 1. Introduction 2. Gas Laws 3. The Ideal Gas Equation 4. Sketching of Graphs Using Ideal Gas Equation 5. The Kinetic Theory of Gases 6. Real Gases and Ideal Gases 7. Mixture of Gases 8. Vapour Pressures 1. INTRODUCTION Resources 1. Chemistry The Molecular Nature of Matter and Change, Silberberg 2. Chemistry, Cann and Hughes 3. Chemistry Principles and Practice, Reger, Goode and Ball 4. https://phet.colorado.edu/en/simulation /gas-properties Gases are made up of particles that are separated by large distances (due to weak intermolecular forces between the particles) and these particles are constantly moving around. These constant movements in a container result in constant collisions with ' • • • / • ' 1 j the walls of the container, giving rise to the phenomenon known as the • • - • \ e "pressure" of the gas. __ @ ., _ • The gas particles are constantly moving as they possess kinetic energy (K.E.). The amount of K.E. depends on the temperature of the gas. In summary, the gaseous state is characterised by the following physical properties: • Gases do not have a fixed shape and volume, i.e. gases assume the volumes and shapes of their containers. • Gases are highly compressible and gas volume changes greatly with pressure. • Gases exert pressure equally in all directions. • Gases mix evenly and completely when confined to the same container. • Gases have much lower densities than solids or liquids. • Gases are poor heat conductors, i.e. good insulators. 1

2. GAS LAWS Over the past few centuries, scientists performed multiple experiments to understand the common behaviors of gases. They have observed that a gas's physical condition depends on four measurable macroscopic properties: p = pressure exerted by the gas V = volume occupied by the gas T = temperature of the gas n = amount of the gas SI units Pa m3 K mol Through a series of experimental studies, the relationships between these four variables are expressed in the following gas laws. 2.1 Avogadro's Law Avogadro's hypothesis states that at constant T and p, gases of the same volume contain the same number of particle