Intro. to Chemistry: Gas Laws 1

Mission Possible The recent Odyssey probe to mars has sent back a sample of the Martian surface, called Oobleck. Your job is to determine if it is a solid, liquid or gas. As a group, decide what criteria you’ll use to make the decision using Yes/No questions. Test the Oobleck and then report your results to me. Your report must explain the tests you did, their results, and justification for your decision. . . 2

Thermal energy vs. Temperature Temperature measures the speed of the particles. (kinetic energy) Thermal energy measures the total energy in the substance. (includes vibrational and kinetic energy) A boiling cup of tea at 100°C will have a higher temperature than a swimming pool at 25°C, but the tea has less thermal energy. A pool has more matter with vibrational (unused) energy, but that matter is moving slower. A slow moving train can hold more than a fast moving car. 3

Thermal Expansion and Kinetic Theory Objects expand when heated. Expansion joints, thermometers and hot air balloons. When the temperature is increased molecules move / vibrate faster and vice versa. Water is the exception to the rule. Water molecules lock themselves together with empty spaces between them. 4

Amorphous Solids Some materials do not have a distinct melting point, but melt over a range of temperatures. Called Amorphous solids Examples: Butter Glass 5

Pressure Amount of force per area. Pressure = F/A If you increase the area, you reduce the pressure. Unit is Pascal (Pa) 1 Pascal is very small, so normally given as kilopascal (kPa) Atmospheric Pressure is 101.3 kPa 6

Pressure Examples 7

Air Pressure Kinetic Theory states particles are in constant motion. At some point they’ll collide with the container’s edge. Air pressure is due to gas particles colliding with container. 8

Boyle’s Law (1662) As volume decreases; the pressure increases. Inverse (opposite) relationship. Only valid if temperature is constant. P1V1 = P2V2 Pressure increase due to more collisions per time. Filling up a smaller balloon with the same amount of gas as a big balloon. 9

Boyle’s Law Practice #1 A balloon has a volume of 10.0 L at a pressure of 101 kPa. What will be the new volume when the pressure drops to 43 kPa? Known: Unknown: Formula: Solve: 10

Boyle’s Law Practice #2 A volume of helium occupies 11.0 L at 98.0 kPa. What is the new pressure if the volume is reduced to 5.0 L? Known: Unknown: Formula: Solve: 11

Charles’s Law (1787) As temperature increases; volume increase. Proportional (same way) relationship. Only valid if pressure is constant. T1 / V1 =T2 / V2. As temperature increases, the particles travel faster and can cover more ground. Examples: Basketball Bread Dough 12

Absolute Zero The lines for all gases seem to point to a common point when plotting Temperature vs. Volume. Common y-intercept at -273°C. Volume at would theoretically be zero on the graph which is not possible. Temperature called absolute zero – nothing colder. All particle motion stops! 13

Kelvin Scale Set -273°C equal to 0 Kelvin. Add 273 to any Celsius temperature to get Kelvin. To do Charles’s Law calculations, temperature must be in Kelvin. Bonus Question: Which scale makes the most sense? Which one do we use? 14

Charles’s Law Practice #1 A gas at 300K has a volume of 2.0L what is the new volume if the gas is cooled to 273 K? Known: Unknown: Formula: Solve: 15

Charles’s Law Practice #2 A gas bubble in bread dough at 20°C has a volume of 20mL. What is the volume of the bubble when the dough is cooked in to bread at 125°C? Known: Unknown: Formula: Solve:

Temperature – Pressure Relationship If the container’s volume is kept constant; the pressure will increase as the temperature increases. Particles are traveling faster, so they hit the container with more force. Examples: Aerosol Can Tire pressure in the winter

Now let’s do a Gas Laws Simulation… 18