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Transcript of Gas Laws
Why scuba divers get "the bends"?
Why popcorn "pops" when it is heated? Gases Do you remember the
Properties of Gases? What 3 factors affect gas pressure? What do all of these
questions have in common? Gases are easily compressed
because of the space between
the particles in a gas.
Compressibility- a measure of how much the volume of matter decreases under pressure. Volume A measure of the space occupied by a sample of matter (V) Temperature A measure of the average kinetic energy of particles in matter (T) # of Moles (n) The amount of gas particles What is gas pressure? Gas pressure results from the force exerted by a gas per unit surface area of an object
Due to collisions of gas particles with the object There are lots of different units for pressure, volume, and temperature.
Today we are going to practice converting between units to make some of the math we do later in the unit a lot easier. Gas
Law Gay-Lussac's Law The relationship between pressure (P) and temperature (T) Pressure and temperature have a direct relationship when volume is held constant. P P The Relationship between pressure (P) and volume (V) Pressure and Volume have an inverse relationship P V =P V The relationship between temperature (T) and volume (V). Temperature and volume have a direct relationship when pressure is held constant. V V What will happen to the volume of the balloon if we take it to the top of the mountain? Inverse = when one variable increases, the other decreases
ex-The harder you push on the brake, the slower your car moves. What does inverse mean? 1 1 2 2 A 2.0L balloon is taken from Woodland Park, where the atmospheric pressure is 0.75 atm, to the top of Pikes Peak, where the atmospheric pressure is 0.54 atm. What will the balloon's volume be at the top of Pikes Peak? 1 2 T T 1 2 = What would happen if we placed a balloon in the freezer? Since we don't have a freezer in this room...let's take a look at when a balloon is placed in something even colder...liquid nitrogen! What does direct mean? Direct - When one variable increases, the other does too, and vice versa
Ex: When you push on the gas pedal harder, the car goes faster Remember that T must be in Kelvin! A balloon inflated in a room at 24 C has a volume of 4.00L. The balloon is then heated to a temperature of 58 C. What is the new volume if the pressure remains constant? If you think about tires looking deflated in the winter, what two variables are changing? So when temperature goes up, pressure goes up, and vice versa. 1 2 T T 1 2 = Remember T must be in Kelvin!!! The pressure in a car tire is 198 kPa at 27 C. After a long drive, the pressure is 225 kPa. What is the temperature of the air in the tire? Assume that the volume is constant. The Combined Gas Law That's a lot of different formulas to remember....Is there an easier way to remember all of these relationships? Combines
and Gay-Lussac's Law
into a single formula Describes the relationship between pressure, volume and temperature P V P V T T 1 1 1 2 2 2 = The volume of a gas-filled balloon is 30.0L at 313K and 153 kPa pressure. What would the volume be at standard temperature and pressure? If one of the variables is held constant, just don't use that part of the equation because it would cancel out anyways. For example, to use only pressure and volume when temperature is constant, it is easy to derive Boyle's Law from the Combined Gas Law. P x V = P x V x T T 1 2 2 2 1 1 Ideal Gas Law So far we've worked with 3 of the 4 variables of a gas: P, T, and V There's a 4th variables to consider: the amount of gas in the container.
Always expressed in moles
(n) PV=nRT *R is the Ideal Gas Constant R= 8.31 L x kPa
mol x K
R= 0.0821 L x atm
mol x K Your units for P,V,n, and T must match the constant that you use!!!! Ideal gas vs. Real gas An Ideal gas would follow gas laws at all conditions of pressure and temperature. It's particles would have no volume and there would be no attraction between particles. Ideal gases do not actually exist, but under most conditions real gases behave like ideal gases.
Real gases differ most from ideal gases at low temperatures and high pressures. A deep underground cavern contains 2.24 x 10 L of methane gas at a prssure of 1.50 x 10 kPa and a temperature of 315K. How many moles of methane gas does the cavern contain? 6 3