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GAS LAWS 2014 http://www.nclark.net/GasLaws GAS LAWS Charles’ Law (slide 4) Boyle’s Law (slide 31) Guy Lusaac’s Law (slide 77) LeChatelier’s Principle (slide 105) Ideal Gas Law (slide ) PRESSURE CONVERSIONS STP means standard temperature and pressure 1 standard atmosphere = 1.000 atm = 760.0 mm Hg = 760.0 torr =101,325 Pa = 14.69 psi ***all of these equal each other!*** Temperature: 0 ˚C or 273 K CHARLES LAW CHARLES’S LAW *Constant amount of gas at a constant pressure Volume of a gas increases with temperature. (Gases expand with heat). ↑T=↑V Jacques Charles proposes Charles's Law. 1787 ↓T=↓V The formula for the law is: V1/T1 = V2/T2 Where: V1 is the initial volume T1 is the initial temperature V2 is the final volume T2 is the final temperature ***temperature MUST be in Kelvin (absolute zero) NOT oC or oF!*** Set up of Demonstration. Blow up two similar balloons so they have the same circumference. Place balloon in ice water on one side to 500 ml. Place equal balloon in hot water on one side to 500ml. Put small block and weight, or use finger to depress balloon under water. Sketch/Record difference in volume between the balloons. How does temperature effect the volume of a gas? Think about the gas molecules in each balloon. DEMONSTRATION - Balloon in hot and cold water --What happens?? - Glass bottle with balloon in hot water Demonstration: Fit a balloon to the top of a glass bottle and place in pan with water. Place on top of heat source and observe. Demonstration: Fit a balloon to the top of a glass bottle and place in pan with water. Place on top of heat source and observe. This law means that when the temperature goes up, the volume of the gas goes up. This law means that when the temperature goes up, the volume of the gas goes up. This law means that when the temperature goes up, the volume of the gas goes up. This law means that when the temperature goes up, the volume of the gas goes up. This law means that when the temperature goes up, the volume of the gas goes up. This law means that when the temperature goes up, the volume of the gas goes up. This law means that when the temperature goes up, the volume of the gas goes up. This law means that when the temperature goes up, the volume of the gas goes up. This law means that when the temperature goes up, the volume of the gas goes up. This law means that when the temperature goes up, the volume of the gas goes up. This law means that when the temperature goes up, the volume of the gas goes up. This law means that when the temperature goes up, the volume of the gas goes up. This law means that when the temperature goes up, the volume of the gas goes up. When the temperature goes down, the volume of the gas decreases . http://group.chem.iastate.edu/Greenbowe/s ections/projectfolder/flashfiles/gaslaw/charl es_law.html Station 2 Microwave Popcorn Key Concept ~ When the temperature of a gas is increased, its volume will increase. Students will be micro waving small amounts of popcorn in a clear bowl. Popcorn pops when the moisture inside boils and expands, bursting the kernel open. Instructions: Place about two tablespoons of popcorn in the clear plastic bowl. Put the top on the bowl and place in the microwave. Close the microwave door and turn the microwave on high. Watch as closely as you can as the popcorn kernels begin to pop, but of course DO NOT OPEN THE DOOR! As soon as the vigorous popping stops, turn off the microwave. Questions: Describe what you see (yeah, I know, but try). What do you think makes the popcorn pop? Put your popcorn in a paper bag and then squirt in some butter if you wish. Station 9 Super Duster & Office Buster Key Concept ~ When the volume of a gas increases, its temperature will decrease. Obtain a can of compressed "air," such as those used to clean electronic equipment. As you depress the nozzle, the gas inside (typically an HFC) responds to the reduced pressure by "boiling" or rapidly turning into a gas. This is an endothermic process so the can gets extremely cold (can even cause frost-bite if you hold it too long.) I like the students to relate this to the phenomenon of water boiling at lower temperatures at high altitudes due to the lower pressure. (Lots of campers know this very well.) The classic Drinking Bird uses a similar concept and makes a good companion to this station. Simply challenge the students to explain the bird's motion. Instructions: Wrap your hand around one of the duster cans. Make sure your palm is in complete contact with the can. Now, depress the nozzle. Questions: What do you feel? Why? Shake the can. What do you notice? Try to explain what happens when you depress the nozzle - See more at: http://www.arborsci.com/cool/chemistry-gaslaws-smorgasborg#sthash.Qy9PndDT.dpuf Other Examples Of Charles’ Law When temperatures get colder, you may need to add some more molecules to get the safe PSI for your vehicle. Copyright © 2010 Ryan P. Murphy You may notice that your sports equipment doesn’t work well when you go out into your garage in the winter. The air molecules are moving very slowly so the ball is flat. Copyright © 2010 Ryan P. Murphy You may notice that your sports equipment doesn’t work well when you go out into your garage in the winter. The air molecules are moving very slowly so the ball is flat. Copyright © 2010 Ryan P. Murphy A 2.0L sample of air is collected at 298 K and then cooled to 278 K. The pressure is held constant at 1.0 atm. a. Does the volume increase or decrease? b. Calculate the volume of air at 278 K. Step One: Write down the information given V1 = 2.0L V2= ? and check units. T1 = 298 KchangeT2 = 278 K sameP = 1.0 atm P1 = 1.0 atm 2 Step Two: Write down the correct formula. V1/T1 = V2/T2 Step Three: Plug the given information into the formula and solve for the unknown variable. V1/T1 = V2/T2 2.0 = 298 278 V2 (2.0)(278) = V2 (298) 298 298 Step Four: Record the two answers. a. The volume will decrease b. V2 = 1.9L BOYLES LAW BOYLE’S LAW: ↓ volume = ↑ pressure ↑ volume = ↓ pressure 1662, Robert Boyle Pressure and Volume are inversely proportional. Very Important! Record in Journal. Activity! Syringes Activity! Syringes Depress plunger on the syringe. Activity! Syringes Depress plunger on the syringe. Cover hole with finger. Activity! Syringes Depress plunger on the syringe. Cover hole with finger. Try and pull handle (gently please). Why is it difficult? Keep thumb on opening. Activity! Syringes Depress plunger on the syringe. Cover hole with finger. Try and pull handle (gently please). Why is it difficult? Keep thumb on opening. Activity! Syringes Answer: It was difficult because your finger created a sealed vacuum and prevented air from entering the chamber. Keep thumb on opening. Activity! Syringes Answer: It was difficult because your finger created a sealed vacuum and prevented air from entering the chamber. Atmospheric pressure is 1 kilogram per square centimeter at sea level. Keep thumb on opening. Activity! Syringes (Opposite) Activity! Syringes (Opposite) Fill syringe. Activity! Syringes (Opposite) Fill syringe. Cover hole with finger. Activity! Syringes (Opposite) Fill syringe. Cover hole with finger. Try and push handle (gently please). Activity! Syringes (Opposite) Fill syringe. Cover hole with finger. Try and push handle (gently please). How does this represent Boyles Law? Activity! Syringes (Opposite) How does this represent Boyles Law? Activity! Syringes (Opposite) How does this represent Boyles Law? Answer: As you depress the plunger, you increase pressure and the volume of the gas is decreased. Activity! Syringes (Opposite) How does this represent Boyles Law? Answer: As you depress the plunger, you increase pressure and the volume of the gas is decreased. Please determine how many milliliters you were able to compress the gas inside using the numbers on the syringe. Activity! Syringes (Opposite) How does this represent Boyles Law? Answer: As you depress the plunger, you increase pressure and the volume of the gas is decreased. Please determine how many milliliters you were able to compress the gas inside using the numbers on the syringe. Answer: You should be able to compress the gas to about 50% of it’s starting volume by hand and then it gets difficult. Can’t wait to eat my yogurt.” “ As you inhale, your diaphragm flattens out allowing your chest to expand and allows more air to flow into your lungs. As you inhale, your diaphragm flattens out allowing your chest to expand and allows more air to flow into your lungs. Air pressure decrease, air then rushes into your lungs. As you exhale, your diaphragm relaxes to a normal state. Space in chest decreases. As you exhale, your diaphragm relaxes to a normal state. Space in chest decreases. Air pressure increases, air then rushes out of your lungs. Which is a inhale, and which is a exhale? A B Which is a inhale, and which is a exhale? A B Which is a inhale, and which is a exhale? Inhale A B Which is a inhale, and which is a exhale? Inhale A B Which is a inhale, and which is a exhale? Inhale Exhale A B Which is a inhale, and which is a exhale? A A B B Which is a inhale, and which is a exhale? A A B B Which is a inhale, and which is a exhale? Inhale A A B B Which is a inhale, and which is a exhale? Inhale A A B B Which is a inhale, and which is a exhale? Inhale Exhale A A B B Cartesian Diver to Display Boyle's Law One 2-liter bottle (clear) One small glass dropper Water Once you've managed to gather these supplies, it would be advised to find a handyman or somebody skilled in construction/engineering to assist in deciphering the following steps: Fill the 2 liter bottle between 2/3 and 3/4 full of water. Take your eyedropper, the "diver" and fill it with just enough water so that the top of the dropper is just buoyant enough to tread the water. Apply the lid to the 2 liter bottle. It must be airtight! Squeeze the bottle. Observe. If you have successfully followed the instructions, good for you. Your Cartesian diver should dive to the bottom as you squeeze the bottle. That's Boyle's law in action! When you squeeze inward, you are reducing the volume of the bottle. As we know, this reduction in volume increases the pressure of all of the gas, including what is contained in your eyedropper. This increase in pressure pushes against the water, forcing more water up into the eyedropper. As you can see, this additional water decreases the diver's buoyancy, causing it to "dive" to the bottom. Stop squeezing the bottle and everything returns to normal, allowing your diver to ascend back to the water's surface. You would be keen to let go slowly, so your diver doesn't ascend too quickly. Wouldn't want it getting the bends! The Bends (Decompression Sickness) – Bubbles form in blood if you rise to quickly because of the rapid decrease in pressure. Copyright © 2010 Ryan P. Murphy The Bends (Decompression Sickness) – Bubbles form in blood if you rise to quickly because of the rapid decrease in pressure. A diver must save time to travel to surface slowly so body can adjust. Copyright © 2010 Ryan P. Murphy BOYLE’S LAW Inverse ↑ P : ↓ V Formula: P1V1 = P2V2 This works because, if the volume of * a constant amount of gas a container is increased, there is a greater area in which the particles of gas inside the container can move. * constant temperature Since the particles have more space, there is less force exerted on the walls of the container by the particles and therefore, less pressure. What pressure is required to compress 196.0 liters of air at 1.00 atmosphere into a cylinder whose volume is 26.0 liters? Step One: Write down the information given and check units. P1 = 1 atm V1 = 196 L, P2 = ? V2 = 26 L Step Two: Write down the correct formula. P1V1 = P2V2 Step Three: Plug the given information into the formula and solve for the unknown variable. (1 atm) (196 L) = (P2) (26 L) P2 = 7.5 atm Freon-12 was a widely used refrigerant but has been replaced by other refrigerants that do not lead to the breakdown of the ozone layer. Consider a 1.5 L sample of Freon-12 gas at a pressure of 56 torr. If the pressure is changed to 150 torr at a constant temperature…. a. Will the volume of gas increase or decrease? b. What will be the new volume of the gas? Step One: Write down the information given and check units. V1 = 1.5 L P1 = 56 torr V2= ? P2 = 150 torr Step Two: Write down the correct formula. P1V1 = P2V2 Step Three: Plug the given information into the formula and solve for the unknown variable. P V =P V 1 1 2 2 (56)(1.5) = (150)(V2) 150 150 Step Four: Record the two answers. a. The volume of gas will decrease b. V = 0.56 L GUYLUSAAC’S LAW GUY LUSAAC’S LAW French chemist Joseph Louis Guy-Lussac in 1802 = the pressure of a fixed mass and fixed volume of a gas is directly proportional to the gas's temperature ↑ temperature = ↑ pressure ↓ temperature = ↓ pressure P/T=k Where: P is the pressure of the gas T is the temperature of the gas (in kelvins) k is a constant When comparing two substances: P1/T1=P2/T2 As pressure increases, temperature increases. Copyright © 2010 Ryan P. Murphy As pressure increases, temperature increases. As pressure decreases, temperature decreases. Copyright © 2010 Ryan P. Murphy + + This photoshop job might look “Funny”. Caution! Graphic Images of burns / the dangers of pressure and temperature. The consequences of severe burns and explosions are not “funny”. Copyright © 2010 Ryan P. Murphy BOILING WATER AT ROOM TEMPERATURE ↑ pressure = ↑ temperature Describe what should happen? What does happen? EXAMPLE: Five grams of octane (C8H18) and enough oxygen to burn it are in an automobile cylinder compressed to 20 atm at 28°C. The mixture explodes and heats the cylinder to 150°C. What is the pressure in the (same sized) cylinder after the explosion? P1 = 20 atm T1 = 301K, P1 / T1 = P2 / T2 P2 = ? T2 = 423 K (20)/(301) = (P2)/(423) P2 = 28.4 atm EXAMPLE 2 A 20 L cylinder containing 6 atm of gas at 27 °C. What would the pressure of the gas be if the gas was heated to 77 °C? P1 = T1 = P2 = T2 = P1 / T1 = P2 / T2 EXAMPLE 2 A 20 L cylinder containing 6 atm of gas at 27 °C. What would the pressure of the gas be if the gas was heated to 77 °C? P1 = 6 atm T1 = 27 +273 = 300K P2 = ?? T2 = 77+273 = 350K P1 / T1 = P2 / T2 EXAMPLE 2 A 20 L cylinder containing 6 atm of gas at 27 °C. What would the pressure of the gas be if the gas was heated to 77 °C? P1 = 6 atm T1 = 27 +273 = 300K P2 = ?? T2 = 77+273 = 350K P1 / T1 = P2 / T2 (6 atm) x (350K) = (P2) (300K) P2 = 7atm PRESSURE CONVERSIONS STP means standard temperature and pressure 1 standard atmosphere = 1.000 atm = 760.0 mm Hg = 760.0 torr =101,325 Pa = 14.69 psi ***all of these equal each other!*** Temperature: 0 ˚C or 273 K LE CHATELIER’S PRINCIPLE If a stress is applied to a system at equilibrium, the position of the equilibrium will shift to reduce the stress. 3 TYPES OF STRESS: 1. 2. Change amount of reactants and/or products Change Pressure 1. 2. 3. 3. Only affects gases b/c partial pressures ( and concentrations) change, a new equilibrium must be reached System will move in direction that has least moles of gas Change in Temperature