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

1) State the basic assumptions of kinetic theory, with reference to ideal gases 2) State properties of an ideal gas. 3) Compare Real and Ideal gases 4) 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.

Based on what is observed put forward at least two theory on gases

 Matter consists of particles in a state of constant, random motion  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  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.

 Collisions between particles are ‘perfectly’ elastic  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 molecules exert no force on one another. The only interaction between molecules are their elastic collisions Z.A. Mason-Andrews BSc. (Hons), Dip.Ed.

 What are the characteristics of a gas behaving most like a gas? Z.A. Mason-Andrews BSc. (Hons), Dip.Ed.

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.

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

 Gases behave ideal under conditions of high temperature 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.

 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.

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increases decreases  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.

 Volume varies inversely with Pressure Z.A. Mason-Andrews BSc. (Hons), Dip.Ed.

 Looks at the relationship between volume and temperature. Z.A. Mason-Andrews BSc. (Hons), Dip.Ed.

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increases increases  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.

When Charles’ Law is extended to extremely low temperatures, the volume of the ideal gas should be zero. Does this occur? Explain your answer ?

 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  Kelvin temperature must be used when performing Gas Law calculations  Kelvin temperature must be used when performing Gas Law calculations. Z.A. Mason-Andrews BSc. (Hons), Dip.Ed.

 Predict what happens to a gas when temperature increases and its volume is kept constant. Z.A. Mason-Andrews BSc. (Hons), Dip.Ed.

 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 constant volume law  The relationship between the temperature and pressure of a gas at constant volume is called the constant volume law  P 1 /T 1 = P 2 /T 2  P 1 /T 1 = P 2 /T 2 where P 1 and T 1 are the initial pressure and absolute temperature of a gas, and P 2 and T 2 are its final pressure and temperature. Z.A. Mason-Andrews BSc. (Hons), Dip.Ed.

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

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.