Chemistry - The Characteristics of gases

Characteristics of gases
Gases are fluids, which means they flow. They are able to flow because they are relatively far apart and therefore are able to move past each other freely. Gases also have a low density and much of the volume occupied by a gas is empty space. Another property of gases are that they are highly compressible. What this means, is you can force gas molecules to move closer together by reducing the about of volume the gas molecules have to move around. This increases the pressure because the molecules are being forced to occupy a smaller space but want to reach equilibrium with the surrounding environment. Lastly, gases completely fill a container. Gas particles are constantly moving around and do not settle, allowing a gas to expand and fill the entire volume of a container.
Pressure is the amount of force exerted per unit area of surface. The unit of force in SI units in pressure is the newton. One newton is the force that gives an acceleration of 1 m/s^2 to the object whose mass is 1 kg (1 newton = 1kg x 1 m/s^2 = 1N). The SI unit of pressure is the pascal, Pa, which is the force of one newton applied over an area of one square meter (1 Pa = 1 N/1 m^2).
According to the kinetic-molecular theory, the behavior of physical systems depends on the combined actions of the molecules constituting the system. Explained, this means that the gas particles are in consistent rapid, random motion. The theory also states that the particles of a gas are very far apart relative to their size. This idea explains the fluidity and compressibility of gases. Gas particles collide with each other and with the walls of their container. The kinetic-molecular theory states that the pressure exerted by a gas is a result of collisions of the molecules against the walls of the container. Also, the theory considers collisions of gas particles to be perfectly elastic and the total energy of the system remains constant. Gas temperature is also proportional to average kinetic energy. Heat increases the energy of random motion of a gas, but not all molecules are traveling at the same speed. As a result of multiple collisions, the molecules have a range of speeds.

The Gas Laws
Boyle's law is the law that states that for a fixed amount of gas at a constant temperature, the volume of the gas increases as the pressure of the gas decreases and the volume of the gas decreases as the pressure of the gas increases. The mathematical expression for this law is PV = k, where P = The pressure exerted by the gas, V = Total volume occupied by the gas, and k is the outcome. If the temperature and the number of particles are not changes, the PV product remains the same, and the mathematical expression is P1V1 = P2V2 (numbers are subscripts).
Example: A given sample of gas occupies 500 mL at 1.25 atm. The pressure is increased to 2.25 atm, while the temperature remains the same. What is the new volume of the gas?
(1) The initial volume and pressure and the final pressure are given. Determine the final volume.
P1 = 1.25 atm V1 = 500 mL
P2 = 2.25 atm V2 = ?
(2) Place the known quantities into the correct places in the equation relating pressure and volume.
P1V1 = P2V2
(1.25 atm)(500 mL) = (2.25 atm) V2
(3) Calculate.
V2 = (1.25 atm)(500 mL) / 2.25 atm = 277.78 mL
(4) Verify your results. The pressure was almost doubled. So the new volume should be approximately one-half the initial volume. The answer is therefore reasonable.
Charles's Law is the law that states that for a fixed amount of gas at a constant pressure, the volume of the gas increases as the temperature of the gas increases and the volume of the gas decreases as the temperature of the gas decreases. This shows the direct relationship between temperature and volume. The mathematical expression for this is V/T = k, where V is the total volume occupied by the gas, T is the temperature in kelvins of the gas, and k is the outcome. IF all other conditions are kept constant, V/T will remain the same. Therefore, Charles's law can be also expressed as V1/T1 = V2/T2.
Example: A balloon inflated to 1000 mL at 24 degrees Celsius. It is immersed in a dry-ice bath at -125 degrees Celsius. What is the volume, assuming the pressure remains constant?
(1) The initial volume and temperature and the final temperature are given.
V1 = 1000 mL T1 = 24C
V2 = ? T2 = -125C
(2) Convert the temperatures from degrees Celsius to kelvins.
T1 = 24C + 273 = 294 K T2 = -125C + 273 = 148 K

V1/T1 = V2/T2

1000mL/194K = V2/148K
(3) Calculate
V2 = (1000 mL)(148 K) / 294 K = 503.40 mL
(4) Verify your results. Charles's law tells you that volume decreases as temperature decreases. The temperature decreases by about one half, and according the the calculation, so did the volume. The answer is therefore reasonable.

Gay-Lussac's law is the law that the pressure of a gas at a constant volume is directly proportional to the absolute temperature. The mathematical expression for this lae is P = kT, where P = Pressure exerted by the gas, k is the outcome, and T = Temperature in kelvins of the gas. The equation can be rearranged to the following form: P/T = k. At a constant volume, the following equation applies: P1/T1 = P2/T2.
Example: A aerosol can containing gas at 163 kPa and 20 degrees Celsius is heated to 59 degrees Celsius. Calculate the pressure in the heated can.
(1) The initial pressure and temperature and the final temperature are given. Determine the final pressure.
P1 = 163 kPa T1 = 20C
P2 = ? T2 = 59C
(2) Convert the temperatures from degrees Celsius to kelvins:
T1 = 20C + 273 = 293K T2 = 59C + 273 = 332K

P1/T1 = P2/T2

163 kPa/293K = P2/332K
(3) Calculate
P2 = (163 kPa)(332 K)/293 K = 184.70 kPa
(4) Verify your results. The temperature of the gas increases by about 13%, the the pressure should increase by the same proportion. The answer is therefore reasonable.

Avogardo's law is the law that states that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules. Avogardo's law is important in determining the formulas of chemical compounds because it allows for scientists to find the volume of 1 mol of an gas at STP.