Kinetic theory

1. Gas Laws and Practical Applications Kinetic theory Z.A. Mason-Andrews BSc. (Hons), Dip.Ed.

2. Objectives • State the basic assumptions of kinetic theory, with reference to ideal gases • State properties of an ideal gas. • Compare Real and Ideal gases • Calculations (Boyle’s, Charles’, Ideal Gas equation, combined gas equation, Pressure law or Constant Volume Law, Combined Gas Equation) Z.A. Mason-Andrews BSc. (Hons), Dip.Ed.

3. Based on what is observed put forward at least two theory on gases Z.A. Mason-Andrews BSc. (Hons), Dip.Ed.

4. Kinetic Theory for Ideal Gases • Matter consists of particles in a state of constant, random motion. These molecules move in a straight line until they collide with the walls of the container. • In an ideal gas, these particles occupy negligible space. Volume of a gas consist mainly of empty space with molecules randomly distributed. • Forces of attraction between particles are negligible. Z.A. Mason-Andrews BSc. (Hons), Dip.Ed.

5. Kinetic Theory for Ideal Gases • Collisions between particles are ‘perfectly’ elastic. (i.e. K. Energy Before Collision = K.Energy After Collision). This means that there are no attractive or repulsive forces involved in collisions and the total energy of the particles remain the same. • The molecules exert no force on one another. The only interaction between molecules are their elastic collisions Z.A. Mason-Andrews BSc. (Hons), Dip.Ed.

6. Kinetic Theory for Ideal Gases • What are the characteristics of a gas behaving most like a gas? Z.A. Mason-Andrews BSc. (Hons), Dip.Ed.

7. Ideal Gases vs Real Gases Ideal Gases Real Gases • Particles occupy negligible space • Negligible forces of attraction • Perfectly elastic collisions between particles • Particles possess a definite shape and volume • Attractive forces exist between particles • Collisions not perfectly elastic, some energy converted into thermal, vibrational and rotational energy. Z.A. Mason-Andrews BSc. (Hons), Dip.Ed.

8. Ideal Gas vs Real Gas • Under what conditions would a real gas behave like an ideal one? • Think about it.... Z.A. Mason-Andrews BSc. (Hons), Dip.Ed.

9. Gases behave ideal under conditions of hightemperature and low pressure. • Increasing the temperature increases the kinetic energy of the particles, this increase in speed causes the particles to overcome the intermolecular forces of attraction between the particles and behave ideally. • Decreasing the pressure allows the particles to spread far apart form each other, allowing intermolecular forces of attraction to approach zero. Z.A. Mason-Andrews BSc. (Hons), Dip.Ed.

10. The Gas Laws • These are results of experiments explaining the responses of gases to changes in physical quantities. • Gases are referred to as ideal gases when they obey the gas laws under all conditions Z.A. Mason-Andrews BSc. (Hons), Dip.Ed.

11. Boyle’s Law http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/animationsindex.htm Z.A. Mason-Andrews BSc. (Hons), Dip.Ed.

12. Boyle’s Law • For an ideal gas, as Volume ↑increases Pressure ↓decreases provided that Temperature is kept constant. (Process is isothermal). • The reverse is true if Pressure increases. • What else should be constant? And Why? Z.A. Mason-Andrews BSc. (Hons), Dip.Ed.

13. Boyle’s Law • Volume varies inversely with Pressure Z.A. Mason-Andrews BSc. (Hons), Dip.Ed.

14. Charles’s Law • Looks at the relationship between volume and temperature. Z.A. Mason-Andrews BSc. (Hons), Dip.Ed.

15. Charles’ Law http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/animationsindex.htm Z.A. Mason-Andrews BSc. (Hons), Dip.Ed.

16. Charles’ Law • For an ideal gas, as Temperature ↑increases Volume ↑increases, provided that Pressure is kept constant. (Process is isobaric). • The relationship between Temperature and Volume is directly proportional. Z.A. Mason-Andrews BSc. (Hons), Dip.Ed.

17. Charles’ Law Z.A. Mason-Andrews BSc. (Hons), Dip.Ed.

18. When Charles’ Law is extended to extremely low temperatures, the volume of the ideal gas should be zero. • Does this occur? • Explain your answer? Z.A. Mason-Andrews BSc. (Hons), Dip.Ed.

19. In reality a gas would change phase before reaching zero volume. • Temperature at which the volume of a gas would become zero if it did not condense is called absolute zero and can be found by extrapolation. • This forms the basis of a new temperature scale called absolute temperature or the Kelvin(K) which uses – 273C as the zero on the scale. • Kelvin temperature = x C + 273 • Kelvin temperature must be used when performing Gas Law calculations. Z.A. Mason-Andrews BSc. (Hons), Dip.Ed.

20. Constant Volume Law/Pressure Law • Predict what happens to a gas when temperature increases and its volume is kept constant. Z.A. Mason-Andrews BSc. (Hons), Dip.Ed.

21. Constant Volume Law or Pressure Law • When a gas collides with the walls of a container it exerts pressure • As temp increase particles will possess grater energy and therefore exert greater pressure • The relationship between the temperature and pressure of a gas at constant volume is called the constant volume law • P1/T1 = P2/T2 where P1 and T1 are the initial pressure and absolute temperature of a gas, and P2 and T2are its final pressure and temperature. Z.A. Mason-Andrews BSc. (Hons), Dip.Ed.

22. Ideal Gas Equation • This is derived from combining Boyle’s Law, Charles’ Law and the Constant Volume law or Pressure Law. • Refer to Chapter. Combined Gas Equation Z.A. Mason-Andrews BSc. (Hons), Dip.Ed.

23. End of Chapter Calculation Questions • Summary activity : • 1.In groups of fours produce a poem, rap, table , mind map, or use diagrams :- • To summarize the kinetic theory of gases • Describe the difference between a real and ideal gas • Include as well in your presentation :-Explanations and equations for Charles’ Law, Boyle’s Law, Constant Volume Law. • Write equations for the ideal gas and combined gas equation Z.A. Mason-Andrews BSc. (Hons), Dip.Ed.

24. End of Lesson Z.A. Mason-Andrews BSc. (Hons), Dip.Ed.