ASRJC H2 Chem 4. Gaseous State

2024 H2 The Gaseous State 2024/Anderson Serangoon JC/Chemistry 1 Anderson Serangoon Junior College H2 Chemistry THE GASEOUS STATE 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. Kinetic Theory of Matter 1.1 Introduction 1.2 Kinetic Theory and their Assumptions as applied to an Ideal Gas 2. Gas Laws: Boyle’s Law, Charles’s Law, Gay-Lussac’s Law and Avogadro’s Law 2.1 Boyle’s Law 2.2 Charles’s Law 2.3 Gay-Lussac’s Law 2.4 Combined Gas Law 2.5 Avogadro’s Law 3. The Ideal Gas Equation 3.1 Calculation of molar gas constant, R 3.2 Other useful forms of Ideal Gas Equation 4. Dalton’s Law of Partial Pressures 5. Deviation from Ideal Behaviour - Real Gases 5.1 Conditions for real gas to approach ideal behaviour 5.2 Graphical representations of deviation from ideal behaviour References 1. Chemistry for Advanced Level, Peter Cann & Peter Huges 2. Understanding Advanced Physical Inorganic Chemistry, Jeanne Tan, Kim Seng Chan 3. Chemistry, The Central Science (10th edition), Brown, LeMay & Bursten 4. A–Level Chemistry, E.N. Ramsden 5. Chemistry in Context, Graham Hill & John Holman Additional Readings 1. Real Gases – Deviations from Ideal Behaviour (Adapted from intro.chem.okstate.edu and www.chemguide.co.uk) 2. The Ideal Gas Law at the Center of the Sun, David B. Clark, Pennsylvania College of Technology 3. The Chemistry Behind the Air Bag, Andreas Madlung, Oregon State University

2024 H2 The Gaseous State 2024/Anderson Serangoon JC/Chemistry 2 1. Kinetic Theory of Matter Quick recap from ‘O’ level Chemistry: 1.1 Introduction • The Kinetic Theory of Matter describes the particles in solids, liquids and gases and the movement of these particles. • The bulk characteristics (i.e. physical properties) of matter can be explained by the arrangement and movement of the particles. • Many pure substances can exist in all of the three states of matter, depending on the conditions of the temperature and pressure. Solids Liquids Gases Volume definite (fixed) definite (fixed) take the volume of the container Shape definite (fixed) take the shape of the container, but do not necessarily occupy all of it occupy the whole of the container Relative compressibility nil almost nil large Relative density large large small Arrangement of particles packed closely together in an orderly manner packed closely together, not in orderly manner far apart (gas consists mainly of empty space) and random Movement of particles vibrate and rotate about fixed positions vibrate, rotate and move as clusters throughout the liquid (translational) vibrate, rotate and translate freely and randomly anywhere within the container Bulk characteristics

2024 H2 The Gaseous State 2024/Anderson Serangoon JC/Chemistry 3 1.2 Kinetic Theory and their Assumptions as applied to an Ideal Gas • It can be observed from the table above that the bulk characteristics of gases differ from that of solids and liquids. • The Kinetic Theory was put forward to explain the behaviour of gases, based on the following assumptions: Basic Assumptions of the Kinetic Theory as applied to an Ideal Gas 1 Gases consist of rigid, spherical molecules that are in continuous, random motion. 2 The volume of the gas molecules is negligible compared to the volume of the container. 3 The forces of attraction between the gas molecules as well as between the gas molecules and walls of the container are negligible. 4 All molecular collisions are perfectly elastic. There is no loss of the kinetic energy during collision. 5 The average kinetic energy of the molecules is proportional to the absolute temperature (measured on the Kelvin scale). In summary, • An ideal gas is a hypothetical gas whose pressure, volume and temperature is completely described by the ideal–gas equation. • Note that ideal gases do NOT exist in real life! Section 5 discusses how gases deviate from ideality.

2024 H2 The Gaseous State 2024/Anderson Serangoon JC/Chemistry 4 2. Gas Laws: Boyle’s Law, Charles’s Law, Gay-Lussac’s Law and Avogadro’s Law • All the four gas laws are discovered experimentally and they express the mathematical relationships among T, p, V and n. Types of mathematical graphs y = m x y =k( 1 x) y = constant Graphical plots to represent ideal gas behaviour 1. Manipulate the ideal gas equation to make the term shown on the y axes of the plot, the subject of the equation. 2. For all terms that are kept constant, replace by k. 3. Replace the term shown on the x-axes of the plot by “x”. 4. Choose the appropriate mathematical graph. 2.1 Boyle’s Law: pressure–volume relationship • Boyle’s Law states that the volume of a fixed amount of gas (n is constant) is inversely proportional to its pressure under constant temperature. Mathematically, V  p 1 or pV = constant This diagram shows the exponential relationship between pressure and volume involving the same no. of moles of gaseous molecules and keeping temperature constant. Using the relationship above, piVi = (4)(V) = (2)(2V) = pfVf 1662 Boyle’s Law 1787 Charles’s Law 1809 Gay-Lussac’s Law 1811 Avogadro’s Law (constant n and T)

2024 H2 The Gaseous State 2024/Anderson Serangoon JC/Chemistry 5 • Graphical representations (at fixed T): pV = constant p = constant ( V 1 ) y = m x • Application of Boyle’s Law: o Scuba diving Scuba divers should not hold their breath whilst ascending to the water surface . For every 10 m of depth that a scuba diver descends, he will experience an additional 1 atm of pressure due to the weight of the water above him. When a diver inhaled a lungful of air at a pressure of 3 atm, and swam quickly to the surface of the water whilst holding his breath, the pressure would decrease by a factor of 3 , the volume of air would increase by a factor of 3, causing severe damage to his lungs. o Shaking a sealed can of fizzy drink results in a great “explosion” when opened The fizz in the drink is actually dissolved carbon dioxide gas, CO 2. Under high pressure, CO2 molecules are forced into the drink in an amount that is greater than what would ordinarily dissolve under atmospheric conditions. Shaking the unopened can of fizzy drink causes bubbles of CO2 to line the walls inside the can. As soon as the can is opened, the pressure in the can decreases and the volume of each bubble increases, most of the excess gas escapes into the room. Tapping the top of the can would dislodge the bubbles from the wall and bottom of the can so that they can float to the top of the