Gas Properties and characteristics

Gas Gas is one of the three states of matter.

Kinetic-Molecular Theory Explains how the properties of gases arise. 1. Particle volume – gas consists of a large collection of individual particles (atoms or molecules) with empty space between them. Volume of each particle is so small compared with the volume of the whole sample that it is considered zero.

Kinetic-Molecular Theory 2. Particle motion – particles of a gas are in constant, random, straight –line motion except when they collide with the container walls or with each other.

Kinetic-Molecular Theory 3. Particle collisions – collisions are elastic, which means that like billiard balls on a frictionless table, the colliding molecules exchange energy but do not lose any energy through friction. Thus, total kinetic energy is constant. Between collisions, molecules do not influence each other by attractive or repulsive forces.

Gas Gasses are characterized as having no attractive forces between the particles. The particles in a gas act like bouncy balls, they are constantly in motion bouncing off other particles of gas, or the solid walls of the container that is holding them.

Pressure The pressure of a gas is the force of all of these gas particles bouncing off the walls of the container.

Pressure The units for pressure are Atmosphere abbreviated Atm. Standard pressure, the air pressure on earth, is 1 atmosphere.

Volume Volume is a measurement of size and space. It is defined as the amount of three-dimensional space something takes up. We measure volume in Liters, abbreviated with a capital L 1 L is made of 1000 mL 1 cm 3 = 1 mL

Volume Since gases have no attractive forces, nothing holds them together They take up way more space than liquids or solids.

Volume Another interesting property of gasses, is that since they have no attractive forces, any gaseous chemical will occupy the same amount of volume. How much volume is it?

Volume 1 mol of ANY gas, will occupy 22.4L of volume here on the surface of earth. Ex. H He Ne O 2 CO 2

Volume vs Pressure The pressure of a gas will change depending on the volume of space the gas occupies. Think of a gas trapped in a balloon If I try to decrease the volume of the balloon by squeezing it, what happens?

Volume vs Pressure The pressure of a gas will change depending on the volume of space that the gas occupies. Think of gas trapped in a balloon, if I try and decrease the volume of balloon by squeezing it, what happens?

POP If I squeeze a balloon to decrease the volume, the pressure builds up on the walls of the balloon and it pops.

POP If I squeeze a balloon to decrease the volume, the pressure builds up on the walls of the balloon and it pops. Pressure is inversely related to the volume of the container. This means that as one increases, the other will decrease.

POP Pressure is inversely (or indirectly) related to the volume of the container. This means that as one increases, the other will decrease.

What happens if you change the size of the container? In a smaller container molecules have less room to move. So they hit the sides of the container more often. As volume decreases pressure increases.

Pressure vs Volume The equation for this relationship mathematically is P 1 V 1 =P 2 V 2 - This is called Boyle’s Law P 1 = initial pressure V 1 = initial volume P 2 = final pressure V 2 = final volume

Temperature The temperature of the gas is a measure of how fast the particles are flying around. Very fast moving particles means the temperature is high. Slow moving particles means the temperature is low.

Temperature We measure the temperature of gases in Kelvin. Kelvin is the absolute temperature scale. 0 Kelvin means the particles are not moving at all, this term also means absolute zero. To convert from Celcius to Kelvin you add 273. To convert from Kelvin to Celcius, you subtract 273

Temperature and Volume Charles’ Law states that the volume of a gas varies directly with the Kelvin temperature, assuming that the pressure is constant. Formula is: V 1 = V 2 T 1 T 2

Pressure and Temperature Gay-Lussac proposed a relationship between pressure and temperature. It is called Gay-Lussac’s Law The formula is: P 1 = P 2 T1T2T1T2

Gay-Lussac’s Law Problem I have a gas tank at 25°C with a pressure of 4 atm. I heat the tank up to 75°C. What is the new pressure in the tank?

Combined Gas Law Boyle’s Law, Charles’ Law and Gay- Lussac’s Law can be combined into one law called the Combined Gas Law The formula is: P 1 V 1 = P 2 V 2 T 1 T 2

Moles and Pressure If we increase the amount of gas in a system without changing the temperature or the volume, what happens to the pressure? More gas particles, more bouncing against the walls, MORE pressure.

Moles and Pressure When we write moles in a gas law equation, the variable is a lower case n. Moles and pressure are Directly related, this means if we increase one, the other must increase if the volume and temperature remain constant.

Moles and Pressure The mathematical relationship for moles and pressure is P 1 = P 2 n 1 n 2

The ideal gas law Since the pressure of a gas, the temperature of a gas, the amount of gas and the volume of space that the gas occupies is all related, we can use a mathematical formula that relates all of these properties.

Ideal Gas law PV = nRT P = pressure in atmospheres n = moles of gas T = Temperature in Kelvin V = volume in Liters R = gas law constant (this value is always.082 if we use the above units)

Ideal Gas Law 1 mol of any gas at 1 atmosphere and 273K always takes up 22.4L of volume. 1 atmosphere and 273K (0°C) is considered standard temperature and pressure (STP.)

Ideal gas law Using the ideal gas law we can calculate for unknown pressures of gas if we are given the other variables. Example : I have a balloon that is 3L, with 2 mols of gas in it at a temperature of 290K, what is the pressure? PV = nRT (P)3L = (2mols)(290K)(.082) P = 15.8atm