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HL1-8.ppt Gas Laws

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Review – Avogadros Law Avogadros Law: Equal volumes of gases at the same T & P contain the same number of molecules. (which means that coefficients in a balanced equation can be read as volumes of gases)

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Review – Molar Volume 1 mole of any gas takes up 22.4 dm 3 of space at STP Standard Temperature (273K or 0 o C) & Pressure (101 kPa or 1 atm) V STP = 22.4 dm 3 / mol Which can be rearranged… n = V STP / 22.4 dm 3 mol

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Review – Molar Volume 1 mole of any gas takes up 22.4 dm 3 of space at STP Standard Temperature (273K or 0 o C) & Pressure (101 kPa or 1 atm) V STP = 22.4 dm 3 / mol Which can be rearranged… n = V STP / 22.4 dm 3 mol

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Other applications of Avagadros law &/or Molar Volume: 1. Determine number of moles (or g) of a given volume of gas at STP. (1.4.2 # 3, part of 5, part of 7) 2. Determine volume of a known quantity (mol or g) of a gas at STP (1.4.2 # 4, part of # 10) 3. Calculate molar mass given information about moles (or g) and volume… and knowing molar volume (1.4.2 # 8) 4. Determine density of a gas at STP (1.4.2 # 9)

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The Ideal Gas Law Q – Can all gases be considered ideal? Most real gases act ideally under normal conditions. They tend to act less ideally when: They have high molar masses Why? They are at very high pressures Why? They are at very low temperatures Why?

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Which of these gases would act the least ideally?

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The Ideal Gas Law PV=nRT where P = pressure in kPa V = volume in dm 3 (Litres) n = moles of gas R = universal gas constant (8.314 kPa dm 3 mol -1 K -1 ) ( if youre using atm, which you wont in IB…) T = temperature in K

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Pressure - You want pressure in kPa… What do you do if it is given in mm Hg? What do you do if it is given in atm?

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The Ideal Gas Law As long as you can remember PV=nRT, you can derive all of the other gas laws. If the number of moles of gas is not changing, we can just solve for n. n=PV/RT Since the moles arent changing, we can set the right side of the equation equal to itself. P 1 V 1 /RT 1 = P 2 V 2 /RT 2 and because R is the same… P 1 V 1 /T 1 = P 2 V 2 /T 2 (combined gas law)

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If you have a problem where one of these variables is held constant, you can simplify the combined gas law by eliminating that variable: P 1 V 1 / T 1 = P 2 V 2 / T 2 P 1 V 1 = P 2 V 2 V 1 / T 1 = V 2 / T 2 P 1 / T 1 = P 2 / T 2

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We now have this collection of gas laws: P 1 V 1 /T 1 =P 2 V 2 /T 2 (Combined Gas Law) P 1 V 1 =P 2 V 2 (Boyles Law) V 1 /T 1 =V 2 /T 2 (Charles Law) P 1 /T 1 =P 2 /T 2 (Gay Lussacs Law)

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Gas Laws TIP #1: Always use K for temperatures because it is an absolute scale (no negatives)T Gas Laws TIP #2: If P or V are on both sides, the units dont matter as long as they are the same on both sides. Gas Laws TIP #3: You must be VERY careful with your units when using the Ideal Gas Law!

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Your Assignment: Read pp Do Ex on pp # 1-10 Identify which gas law you are using to solve the problem… then solve the problem. Show your work…. (at minimum include the set up using some form of a gas law)

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Charles Law Charles's law is an experimental gas law which describes how gases tend to expand when heated. It was first published by French natural philosopher Joseph Louis Gay- Lussac in 1802, although he credits the discovery to unpublished work from the 1780s by Jacques Charles.gas lawgasesFrench natural philosopherJoseph Louis Gay- LussacJacques Charles

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Charles Law T V The following is a more useful way of expressing this law.

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Create a hypothesis for what happened here.

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Heres what really happened. 1. Workers used hot pressurized water to clean the tanker car. 2. Tank was drained. 3. Door was closed and tanker was left overnight. 4. Temperature inside the car plummeted overnight. 5. V/T=V/T (Temp goes down, Volume must go down also)

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