Temperature Measure of KE At the same temperature, heavier molecules have less speed Absolute Zero -273 o C 0 K

Transcription

1 Temperature Measure of KE At the same temperature, heavier molecules have less speed Absolute Zero -273 o C 0 K

2 Kinetic Molecular Theory of Gases 1. Large number of atoms/molecules in random motion 2. Volume of particles negligible 3. Interaction between particles negligible 4. Average kinetic energy constant 5. Average kinetic energy proportional to absolute temperature

3 Kinetic-Molecular Theory - Theory developed to explain gas behavior - To describe the behavior of a gas, we must first describe what a gas is: Gases consist of a large number of molecules in constant random motion. Volume of individual molecules negligible compared to volume of container. Intermolecular forces (forces between gas molecules) negligible. Energy can be transferred between molecules, but total kinetic energy is constant at constant temperature. Average kinetic energy of molecules is proportional to temperature.

4 Standard Atmospheric Pressure 760 mm at 273 K at sea level barometer 1 atm = 760 mm Hg = 760 torr Torricelli pressure of the atmosphere is balanced by pressure exerted by mercury

5 As the gas molecules get closer together, the smaller the intermolecular distance.

6 Kinetic-Molecular Theory This is a model that aids in our understanding of what happens to gas particles as environmental conditions change.

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8 A barometer is a device used to measure atmospheric pressure. The first barometer was introduced by Evangelista Torricelli in the early 1600s. He sealed a long glass tube at one end and filled it with mercury. Inverting the tube into a dish of mercury, the mercury rose to a height of 760 mm.

9 Main Tenets of Kinetic- Molecular Theory 1. Gases consist of large numbers of molecules that are in continuous, random motion. 2. The combined volume of all the molecules of the gas is negligible relative to the total volume in which the gas is contained. 3. Attractive and repulsive forces between gas molecules are negligible. 4. Energy can be transferred between molecules during collisions, but the average kinetic energy of the molecules does not change with time, as long as the temperature of the gas remains constant. The average kinetic energy of the molecules is proportional to the absolute temperature.

10 Pressure Pressure of air is measured with a BAROMETER (developed by Torricelli in 1643)

11 Pressure Hg rises in tube until force of Hg (down) balances the force of atmosphere (pushing up). (Just like a straw in a soft drink) P of Hg pushing down related to Hg density column height

12 Pressur e Column height measures Pressure of atmosphere 1 standard atmosphere (atm) * = 760 mm Hg (or torr) * = inches * = 14.7 pounds/in 2 (psi) *HD only = kpa (SI unit is PASCAL) * HD only

13 Pressure Pressure of air is measured with a BAROMETER (developed by Torricelli in 1643)

14 Measuring Pressure Barometer: a device used to measure atmospheric pressure. Introduced by Torricelli in the early 1600 s He used a glass rod in placed in a tub of Mercury (Hg). When placed in the mercury the glass rod would fill to 760 mm above the dish. This measurement would figured to be atmospheric pressue mm Hg

15 Kinetic-Molecular Theory This is a model that aids in our understanding of what happens to gas particles as environmental conditions change.

16 Main Tenets of Kinetic- Molecular Theory Gases consist of large numbers of molecules that are in continuous, random motion.

17 Main Tenets of Kinetic- Molecular Theory The combined volume of all the molecules of the gas is negligible relative to the total volume in which the gas is contained. Attractive and repulsive forces between gas molecules are negligible.

18 Energy can be transferred between molecules during collisions, but the average kinetic energy of the molecules does not change with time, as long as the temperature of the gas remains constant. Main Tenets of Kinetic- Molecular Theory

19 Main Tenets of Kinetic- Molecular Theory The average kinetic energy of the molecules is proportional to the absolute temperature. Boltzmann distribution plot

20 Units of Pressure Pascals 1 Pa = 1 N/m 2 Bar 1 bar = 10 5 Pa = 100 kpa mm Hg or torr These units are literally the difference in the heights measured in mm (h) of two connected columns of mercury. Atmosphere 1.00 atm = 760 torr Derivation of Pressure / barometer height relationship

21 Pressure Pressure is the amount of force applied to an area. P = F A Atmospheric pressure is the weight of air per unit of area.

22 Mercury Barometer

23 Kinetic Molecular Theory Matter consists of particles (atoms or molecules) in continuous, random motion.

24 Kinetic Molecular Theory: Gases particles in continuous, random, rapid motion collisions between particles are elastic volume occupied by the particles is negligibly small effect on their behavior attractive forces between particles have a negligible effect on their behavior gases have no fixed volume or shape, take the volume and shape of the container