Monoatomic Gas: Made of one atom, like HeMonoatomic Gas: Made of one atom, like He Diatomic Gas: Made of two atoms, like Cl 2 or H 2Diatomic Gas: Made of two atoms, like Cl 2 or H 2 *This is the case for Br, I, N, Cl, H, O, F *This is the case for Br, I, N, Cl, H, O, F Also known as Miss BrINClHOF (Brinklehoff) Polyatomic Gas: Made up of more than two atoms, like CO 2, NO 2, or CH 4 (methane)Polyatomic Gas: Made up of more than two atoms, like CO 2, NO 2, or CH 4 (methane)

 Gases have mass  It is easy to compress a gas  Gases fill their containers completely  Gases diffuse through each other easily  Gases exert pressure on their surroundings  The pressure of a gas depends on its temperature

 Gases are composed of a large number of particles that behave like hard, spherical objects in a state of constant, random motion.  Basically, gas particles are like billiard balls in a 3-D pool table, and they are all moving all over the place all the time in different directions

 These particles move in a straight line until they collide with another particle or the walls of the container.  Then they bounce off, and move again: these collisions are elastic  Gas Molecule Motion Gas Molecule Motion Gas Molecule Motion

 There is no force of attraction between gas particles or between the particles and the walls of the container.  Keep in mind that things aren’t repelled, either….no attraction, no repulsion…

 Collisions between gas particles or collisions with the walls of the container are perfectly elastic. None of the energy of a gas particle is lost when it collides with another particle or with the walls of the container.  This is why gases take the shape of their container!  The energy of the system is constant as long as the pressure and temperature remain constant.

 The average kinetic energy of a collection of gas particles depends on the temperature of the gas and nothing else.  Think back to the fact that temperature is a measure of Kinetic Energy (the random motion of molecules)

 These particles are much smaller than the distance between particles. Most of the volume of a gas is therefore empty space.  Compared to the container, the volume of the gas is zero. So, we say the volume of the container is the volume of the gas  The volume of the gas in an empty soda bottle is?

1. Gases consist of very small particles, each of which has a mass. 2. The distance separating gas particles is very large so much so that we say the volume of the gas is negligible as compared to the volume of the container (the gas itself has no volume) 3. Gases exert no force on one another 4. Gas particles are in random, rapid, constant motion 5. Collisions with other gas particles or the walls of the container are elastic (no energy lost) 6. The average KE of a gas depends on the temperature of the gas

We measure gases in several ways…  Volume = V  Temperature = T  Pressure= P  Number of Moles= n

 Temperature is a measure of heat; more specifically it is the (average) measure of the random kinetic energy of the molecules in an object  Kinetic energy: Energy of motion  More motion = More KE = Higher temperatures  Less Motion= Lower KE = Lower temperatures

 For most scientists, the Celsius scale is used  However, we need to use the Kelvin scale for gas laws

 Why this strange and bizarre scale that uses a boiling point of 373K and a freezing point of 273K for water?  Well, it’s because our “normal” temperature scales are based upon numbers that make sense to use (or not)  (like freezing at 0°C and boiling at 100 °C) or are a bit more convoluted (like the Fahrenheit scale, where zero comes from the temperature of ice, water and NH 4 Cl and body temperature was 98 °F and still water with ice was 32 °F. )

 The Kelvin scale bases temperature on an absolute scale, where temperatures correspond to the amount of motion of the particles  Absolute zero (O K) is when there is no molecular motion (at all)  Scientists have gotten close to zero K, but not quite there.  It exists naturally in deep space

 Calculations using temperature of zero could be undefined or have no value (which really can’t be)  Can’t have negative volumes in our equations, because that is impossible (from using negative temperatures values in the variables)  The Kelvin scale avoids all of these issues

 Is based in Absolute Zero, which is -273°C  0K= -273°C  273K=0°C To convert between K and °C, °C =K or K -273 = °C It’s that simple, which is good since no gas laws calculations can use °C

 We usually measure volume in Liters (L), but sometimes in othermetric units 1L = 1000mL 1L =.001m 3 We will use these conversions- be sure to know them!

 Gas pressure is created by the molecules of gas hitting the walls of the container. This concept is very important in helping you to understand gas behavior. Keep it solidly in mind. This idea of gas molecules hitting the wall will be used often.  Pressure is force measured over an area P=Force/ area and yes, Physics children, Force = mass (acceleration)

 atmospheres (atm)  millimeters of mercury (mm Hg)  Pascals (= Pa)  kiloPascals (= kPa)  Standard pressure is defined as: 1 atm 1atm =760.0 mm Hg 1 atm= kPa

 Manometers- Measure the pressure of a gas as compared to the outside world

 We’ve been here before. Calm down about it.  Remember that 1 mole is 6.02 E 23 pieces of something- in this case, usually molecules of gas (but sometimes atoms, if not a diatomic gas).  Also, 1 mol gas at STP (Standard Temp/Pressure) = 22.4L  “= “means occupies, takes up, etc

 Relates pressure and volume, while temperature and number of moles are constant (so they do not appear in the equation)

P 1 V 1 =P 2 V 2  In a closed rigid container of a gas at a constant temperature, the pressure times the volume remains constant (P 1 V 1 =k)  Pressure and volume are inversely related  The P 1 is the pressure at the first volume (V 1), while P 2 is the pressure at the second volume (V 2 ).

 The product of pressure and volume remains constant as long as the temperature remains constant. (The number of moles must also remain constant.) When volume is high, pressure is low When the volume is low, pressure is high Pressure Volume

 If a balloon with a volume of 3L is under a pressure of 1 atmosphere, determine the new volume if the pressure is changed to.8 atm.  We are given P 1, V 1, and P 2. We are asked to find V 2  Two key words here are new and changed- to ID these measurements as linked (having the same subscript)  What is the new volume?

 Charles’ law relates volume and temperature, at a constant pressure and number of moles in a flexible container. Since the pressure and number of moles are constant, they do not appear in the equation.

V 1 /T 1 =V 2 /T 2  In a closed container of a gas at a constant temperature, the pressure times the volume remains constant (P 1 V 1 =k)  The P 1 is the pressure at the first volume ( V 1), while P 2 is the pressure at the second volume (V 2 ).

 V 1 /T 1 =V 2 /T 2 can be rearranged to read  V 1 T 2 =V 2 T 1  Why would we care to rearrange this? This means no division in the equation. You can use it either way, just remember that they are DIRECTLY PROPORTIONAL.

 As the temperature increases, the volume increases.  As the temperature decreases, the volume decreases.  Temperature and volume are proportionally related.

 Think again about temperature- it is the KE of the gas particles.  Think about what the volume is a result of: the force that the gas molecules are exerting of the container  Think about how if something hits another thing at a higher speed- it hits with more force. More force is pushing harder. Pushing harder means further. This means greater volume when we are dealing with a flexible container!

 Relates pressure and temperature, when volume is kept constant (P 1 /T 1 =k)  P 1 /T 1 = P 2 /T 2 Or  P 1 T 2 =P 2 T 1

 (P 1 V 1 )/ T 1 =(P 2 V 2 )/T 2  Takes all other gas laws into account, even if you can’t see them here (they cross out of the equation)  When in doubt about most of the guy’s laws, you can use this one, because when the pressure, volume, or temperature is constant, you have the law you need.