AP Chemistry Tutorials–01 Chp-05: Kinetic Theory Srinivasan G. Srivilliputhur December 03, 2015

Today’s Overview 1 2 Problems 81 – 93 in the Textbook AP MCQs This is another option for an overview slide.

Kinetic Molecular Theory (KMT) Terminology: Here, the term “molecule” refers to the individual chemical species in the gas, although some gases are composed of atomic species (e.g. the noble gases) KMT: Is a simple microscopic model Accurately explains the gas laws Five Postulates of KMT The various gas laws can be derived from the KMT postulates, which have led to the belief that KMT accurately represent the properties of gas molecules.

Kinetic Molecular Theory (KMT) Five Postulates of KMT Gases are made of molecules that move continuously, travelling in straight lines and changing direction only when they collide with other molecules or with container walls. The gas molecules are negligibly small compared to the distances between them (i.e. their volume is negligible compared to container volume). The pressure exerted by a gas results from their collisions with the container walls. Gas molecules exert no attractive or repulsive forces on each other or the container walls; therefore, their collisions are elastic (i.e. no loss of energy). The average kinetic energy of the gas molecules is proportional to the Kelvin temperature of the gas.

T increases, P increases Amonton’s Law from KMT T increases, P increases WHY? Increased force + more frequent molecular collisions

V decreases, P increases Boyle’s Law from KMT V decreases, P increases WHY? Reduced wall area + more frequent wall collisions

Amount Increases, P constant Avogadro Law from KMT Amount Increases, P constant WHY? Volume increases to yield a constant number of collisions per unit wall area (because P is constant)

Molecular Velocities & Kinetic Energy Microsoft Engineering Excellence Molecular Velocities & Kinetic Energy Observations Very few molecules move at either very low or very high speeds The number of molecules with intermediate speeds increases rapidly up to a maximum, which is the most probable speed (vp), then drops off rapidly Note that the most probable speed, νp, is a little less than 400 m/s, while the root mean square speed, urms, is ~500 m/s. The molecular speed distribution for O2(g) at 300K Microsoft Confidential

Molecular Velocities & Kinetic Energy Microsoft Engineering Excellence Molecular Velocities & Kinetic Energy Observations The molecular speed distribution for N2(g) shifts to the: right and flattens as the temperature increases left and heightens as the temperature decreases Microsoft Confidential

Molecular Velocities & Kinetic Energy Microsoft Engineering Excellence Molecular Velocities & Kinetic Energy Observations The molecular speed distribution for N2(g) shifts to the: right and flattens as the temperature increases left and heightens as the temperature decreases Microsoft Confidential

Microsoft Engineering Excellence (Q-1) 2015 AP Chemistry The three gases are in identical rigid containers under the conditions given in the table below. Microsoft Confidential

Microsoft Engineering Excellence (Q-2) 2015 AP Chemistry The three gases are in identical rigid containers under the conditions given in the table below. Microsoft Confidential

Microsoft Engineering Excellence (Q-3) 2015 AP Chemistry The three gases are in identical rigid containers under the conditions given in the table below. Microsoft Confidential