“He could clear the savanna after every meal “He could clear the savanna after every meal!” UNIT 10: Gases & Phase Changes

Outline of a Gassy Unit 10.1 Properties of Gases 10.2 Temperature and Pressure 10.3 Combined Gas Law 10.4 Ideal Gas Law 10.5 Phase Change Diagrams

10.1 Learning Target I can describe the properties of gases. Shape Volume Density Fluidity Diffusion/Effusion

10.1 – Properties of Gases Shape: indefinite Volume: indefinite Compressible (decrease) Expandable (increase) Tennis ball Marshmallow… Volume: indefinite Indefinite shape – the room air pockets. Fire syringe… cotton ball for compressible.

10.1 – Properties of Gases Density – gases have a low density Small amount of mass in a given space. What would happen if the volume was compressed? Balloon demo…

10.1 – Properties of Gases Gases are fluid! Color Pouring CO2 Many are colorless. Oxygen, nitrogen, and water. Gases with color are poisonous. Iodine

10.1 – Properties of Gases Diffusion Effusion Definition: Molecules of different gases mix easily and spread throughout a container. Gas particles spontaneously pass through a small opening. Example: Ex: Bacon in the morning… or pizza… Ex. Helium balloons

10.2 Learning Target Describe pressure and temperature in terms of kinetic molecular theory. Convert between different units of temperature and convert between different units of pressure.

10.2 – Temperature and Pressure Ideal Gas “Perfect” gas Assumes the following: 1. Gas molecules have no volume. 2. Gas molecules move in straight lines until they collide. 3. Gas molecules are neither attracted nor repelled by one another.

10.2 – Kinetic molecular theory Gas molecules are constantly in motion and collide with each other and with the walls of a container Particles move faster with increased temps Gases are made of mostly empty space and just a few fast moving particles

10.2 – Variables of a Gas (P) Pressure (V) Volume (T) Temperature (n) Amount of gas in moles

10.2 – Variables of a Gas A variable is a factor that is likely to change. Pressure, temperature, and volume of a gas are likely to change. Pressure, volume, and temperature are interdependent. When one variable changes, they all do.

10.2 – Pressure Measures: Force exerted by moving gas particles and by collisions with their container.

10.2 – Pressure Units: atm (atmosphere) - 1 atm of pressure is the average pressure at sea level Important Conversions: 1 atm = 760 mmHg (millimeters of Mercury) = 760 torr = 101.3 kPa (kilo Pascals) = 14.7 psi (pounds per square inch)

10.2 – volume Measures: amount of space that a gas occupies Units: Liters (L) Important Conversions: 1 L = 1000 mL

10.2 – Temperature Measures: average kinetic energy of gas particles. Units: Kelvin (K) The Celsius scale is NOT used for gases because gases can still have kinetic energy at negative and 0o C.

10.2 – Temperature Kelvin Scale and Absolute Zero Absolute Zero = 0 Kelvin represents the temperature at which a gas has NO kinetic energy Atoms at Absolute Zero

oC + 273 = K K – 273 = oC 10.2 – Temperature Converting Temperature Important Conversions: oC + 273 = K K – 273 = oC

10.2 – Standard Temperature and Pressure STP = Standard Temperature and Pressure Exactly 0oC and 1 atm At STP, one mole of gas (6.02 x1023 particles) occupies 22.4 L If a gas is not held at STP, then volume is recalculated

10.3 – Learning Targets I can use the combined gas laws! You will be studying the four variables that effect the behavior of gases. Pressure Temperature Volume Number of moles of gas particles

10.3 – Combined Gas Law Relates pressure, temperature, volume, and moles of a gas Relates initial and final conditions Variables that do not change are constants and are not included in the equation

10.3 – Combined Gas Laws The left side (1) represents the initial conditions of the gas The right side (2) represents the final conditions of the gas

10.3 – Charles’ law What changes? And How? What stays the same? Volume increases, temperature increases What stays the same? Pressure and moles are held constant (toss ‘em)

10.3 – Charles’ law Equation Remember: Temperatures must be in Kelvin

10.3 – Charles’ law Demo

10.3 – Charles’ law Graph Direct Relationship: both variables increase together

10.3 – Charles’ law Example A gas sample at 25 °C and 752 mL is heated to 50 °C , what is the new volume?

10.3 – Gay – Lussac’s Law What changes? And how? As temperature of a gas increases, the pressure also increases What stays the same? Volume and moles are held constant (toss ‘em)

10.3 – Gay- Lussac’s Equation Pressure units on both sides of the equation must be the same Temperature must be in Kelvin

10.3 – Gay- Lussac’s Demo http://www.youtube.com/watch?v=qHDPagByi0o

10.3 – Gay- Lussac’s Graph Direct Relationship: Both variables increase together

10.3 – Gay- Lussac’s Example Q: A gas has a pressure of 0.370 atm at 50.0 °C. What is the pressure at standard temperature?

10.3 – Boyle’s Law What changes? And How? When Pressure increases, Volume decreases What stays the same? Temperature and moles are held constant (toss ‘em)

10.3 – Boyle’s Law Equation P1V1 = P2V2 Remember: Pressure units on both sides of the equation must be the same

10.3 – Boyle’s Law Demo

10.3 – Boyle’s Law Graph Inverse Relationship: an increase in one variable with a simultaneous decrease in the other

10.3 – Boyle’s Law Example Q: A 1.0 L sample of gas is held at standard pressure, 1.0 atm. The pressure of the gas is reset to 152 mmHg. What is the new volume of the gas?

10.3 – Avogadro’s Law Avogadro stated that as the number of moles of a gas increases, volume increases.

10.3 – Avogadro’s Law The temperature and pressure are kept constant.

10.3 – Avogadro’s Law “Demo”

Chemistry Valentines You are like Fluorine, Iodine, and Neon… You are FINe! Are you made of copper and tellurium? Because you are CuTe!

10.3 – Mini Quiz Review P1V1 = P2V2 A container of gas has a volume of 10 L at a pressure of 1.0 atm. What would be the new volume of the gas if the pressure was increased to 2.0 atm?

10.3 – Mini Quiz Review P1V1 = P2V2 A gas sample at 40.0 °C occupies a volume of 2.32 L. If the temp is raised to 75.0 °C, what will the volume be?

10.3 – Mini Quiz Review P1V1 = P2V2 The pressure of a gas in a tank is 3.2 atm at 22 °C. If the temp rises to 60.0 °C, what will be the gas pressure in the tank?

10.3 – Mini Quiz Review P1V1 = P2V2 The number of moles in a balloon changed from 4.01 to 6.03. If the volume of the balloon was originally 1.13 L, what is the new volume?

10.3 – The master Equation The gas left in a used aerosol can is at the pressure of 100.0 kPa at 27 °C. If the can is thrown into the fire, what will the internal pressure of the gas be when its temperature reaches 927 °C?

10.3 – The master Equation A gas at 110 kPa and 30.0 °C fills a flexible container with an initial volume of 2.00 L. If the temperature is raised to 100.0 °C and the pressure increased to 440 kPa, what is the new volume?

Review! When a sample of gas is under lower pressure, with no temperature change, what will happen to… The volume of a gas?

Review! If air is trapped in a syringe at a constant temperature, but more pressure is applied, what will happen to the volume?

Review! What happens to a balloon filled with a light gas outside in the freezing cold? The balloon’s volume?

10.4 Learning Targets Use the ideal gas law.

10.4 – Ideal Gas PV = nRT P = pressure (units can vary) V = volume (Liters) n = moles T = temperature (K) R is the Ideal Gas Constant Use if conditions (P, V, n, or T) DO NOT change

10.4 – Ideal Gas Values of R: (with units) Atm kPa mm Hg or torr

10.4 – Ideal Gas Example 1 A sample of O2 gas collected at 30°C has a volume of 0.25 L and a pressure of 1.3 atm. How many moles of oxygen are present?

10.4 – Ideal Gas Example 2 A sample of He gas contains 0.5 moles. At STP, what is the volume of the gas?