Introduction to the Gas Laws CPS Chemistry
What is a Gas? • A state of matter where there is indefinite volume (will fill its container) and indefinite density (can be compressed) • Gasses are fluids, because like liquids they have the ability to flow • Gasses are made up of randomly moving molecules, but are mostly empty space
Temperature • Temperature is the measure of how hot or cold an object is relative to something else • Temperature in a gas relates to the kinetic energy of the molecules, the hotter the temperature, the faster they move • Temperature in gas law problems is always measured Kelvin, convert all temps to K • Standard temperature is 273K
Pressure • Pressure is force/area, N/m2 or a Pascal • Pressure is directly proportional to applied force • Pressure is indirectly proportional to area • Pressure in gasses is the result of the number of collisions that the molecules make with the container, so the greater the temperature, the greater the pressure
Pressure cont. • Units of pressure are: torr mm of Hg (millimeters of mercury) atm (atmospheres) • Standard Pressure is: 760 torr 760 mm of Hg 1 atmosphere
Volume • Volume is the amount of space that gasses take up, gasses will fully fill any container that they are in • Two units of volume are Cubic centimeters: cc or cm3 Millileters: mL 1 cc = 1 cm3 = 1 mL
Boyles Law • Pressure and volume are inversely proportional, if you increase one, you decrease the other citation
The equation P1V1 = P2V2 This works when the temperature is kept constant. Before you start working with ANY gas law problem, make sure that you have all the same units!
Example 1 • You have 2.0L of hydrogen gas at 3.0 atmospheres, you increase the pressure to 12.0 atm, what is your new volume?
Example 2 • You have 30cm3 of chlorine gas at 1000 torr you change the volume to 90cm3 what is your new pressure? (solve for torr, mm of Hg and atm)
Charles Law • When pressure is kept constant the relationship between Temperature and volume is citation
V1 V2 = T1 T2 The Formula • The formula is
Example 1 • If pressure is held constant, and a 2.0L of Neon gas is heated from 0°C to 100°C, what is the new volume?
Example 2 • If pressure is held constant, and a 850cc of Argon gas is cooled from 50°C to 10°C, what is the new volume?
Gay-Lussac’s Law • “The pressure of a fixed mass of gas at a constant volume varies directly with the temperature (K).” • If you have a certain amount of gas in a fixed sized container, the pressure will change if the temperature changes.
The formula P1= P2 T1 T2
Example 1 A cylinder of compressed gas has a pressure of 4.882 atm on one day. The next day the same cylinder of gas has a pressure of 4.690 atm and its temperature is 8°C. What was the temperature on the previous day in C?
Example 2 The safety limit for a certain can of aerosol stay is 95°C. If the pressure of the gas in the can is 2.96 atm when it is 17°C, what will the pressure be at the safety limit?
Combined Gas Law • When you have all three variables involved (Pressure, Temperature, and Volume) you use the combined gas law P1V1 P2V2 = T1 T2
Example 1 • A 50 mL sample of fluorine gas at 15°C that rises in temperature to 80°C, if the original pressure is 2 atm and increases to 8 atm, what is the new volume?
Example 2 • A 500 cc sample of boron gas at 85°C that cools to 0°C, if the original pressure is 768 torr and increases to 850 torr what is the new volume?
Partial Pressures • The total pressure in a combination of gasses is the sum of all the pressures of each individual gas. Ptot=P1+P2+P3… *all gas pressures must be in the same unit
Example 1 • The total pressure for air in a scuba tank is 1200 torr, if the oxygen has a pressure of 500 torr, the Nitrogen is 350 torr, what is the pressure of the argon gas component?
Ideal Gas Law • All the prior gas laws involve a combination of pressure, temperature, or volume. The ideal gas law also takes into account the number of molecules of gas involved. PV=nRT
Ideal gas law cont. P= pressure = atmospheres V = volume = Liters T = temperature = Kelvin n = number of moles = mol R = gas constant = .0821 L * atm mol * K
Example 1 • A rigid cylinder with a volume of 10.0 liters is filled with neon gas at a pressure of 250. atm at 30°C, how many moles are in the gas?
Example 2 • A 12.0 liter flask at 45°C has 5.00 moles of helium gas, what is the pressure?