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CHAPTER 14 THE BEHAVIOR OF GASES: 14.1 Properties of gases 14.2 The Gas Laws 14.3 Ideal Gases 14.4 Gases: Mixtures and Movements. 14.1 Properties of Gases Why are gases easier to compress than solids? What are the three factors affect gas pressure?. Compressibility:
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14.1 Properties of gases
14.2 The Gas Laws
14.3 Ideal Gases
14.4 Gases: Mixtures and Movements
-Four variables are used to describe a gas.
a. Pressure in kilopascals (P) 1atm. = 101.3kPa = 760mm Hg
1psi = 6.9kPa
b. Volume in Liters (V)
c. Temperature in Kelvin (T) OO C = 273K
d. Number of moles (n)
In most aerosol cans, the bottom curves inward. This serves two functions:
-An ideal gas is one that follows the gas laws at all conditions of pressure and temperature, precisely to the kinetic theory.
-the particles can have no volume and no attraction to other particles in the gas.
-There is no gas at which these assumptions are true.
-However, real gases behave very much like an ideal gas at many conditions of temperature and pressure.
-Real gases differ most from an ideal gas at low temperatures and high pressure.
-Real gases deviate from the ideal
a. When the ratio is greater than 1 and the curve rises above
the ideal gas line. Molecular volume dominates due to
more kinetic energy
b. When the ratio is less than 1 and the curve drops below
the line. Intermolecular attractions dominate.
Since the product is liquid at room temperature, it is simply poured in before the can is sealed. The propellant, on the other hand, must be pumped in under high pressure after the can is sealed. When the propellent is kept under high enough pressure, it doesn't have any room to expand into a gas. It stays in liquid form as long as the pressure is maintained. (This is the same principle used in a liquid propane grill.)
When the valve is open, the pressure on the liquid propellant is instantly reduced. With less pressure, it can begin to boil. Particles break free, forming a gas layer at the top of the can. This pressurized gas layer pushes the liquid product, as well as some of the liquid propellant, up the tube to the nozzle.
When the liquid flows through the nozzle, the propellant rapidly expands into gas. In some aerosol cans, this action helps to atomize the product, forming an extremely fine spray. In other designs, the evaporating propellant forms bubbles in the product, creating a foam. The consistency of the expelled product depends on several factors, including:
The chemical makeup of the propellant and product
The ratio of propellant to product
The pressure of the propellant
The size and shape of the valve system
-How are the pressure, volume, and temperature of a gas related?
-When is the combined gas law used to solve problems?
-Combined Gas Law
For a given mass of a gas at constant temperature, the volume of the gas is inversely proportional to the pressure.
P1 x V1 = P2 x V2
The graph of an inverse
relationship is always
V1 / T1 = V2 / T2
The ratio of the variables is always constant in a direct
relationship and the graph is always a straight line
-The pressure of a gas is directly proportional to the Kelvin temperature if the volume remains constant.
P1 / T1 = P2 / T2
- Describes the relationship among the pressure, temperature, and volume of an enclosed gas.
P1 x V1 / T1 = P2 x V2 / T2
By remembering the combined gas law, all other laws can be derived as long as one variable remains constant.
-How is the total pressure of a mixture of gases related to the partial
pressures of the component gases?
-How does the molar mass of a gas affect the rate at which the gas
effuses or diffuses?