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Chapter 11: Behavior of Gases

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Particles of Ideal vs Real Gas IdealReal have no volumehave their own volume dont attract or repel each other attract each other have elastic collisionshave collisions that are not elastic

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How gases behave Gas behavior is most ideal… –at low pressures –at high temperatures –in nonpolar atoms/molecules **Always use Kelvin temperatures when working with gases

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pressure of a gas is caused by the collisions of the particles in the gas on the walls of their container. Defining Gas Pressure

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The more often gas particles collide with the walls of their container, the greater the pressure

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Defining Gas Pressure more air particles inside the ball mean more mass inside.

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pressure of a gas is directly proportional to its mass. P α M If m then p How are number of particles and gas pressure related?

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At higher temperatures, the particles in a gas have greater kinetic energy. How are temperature and pressure related? move faster and collide with the walls of the container more often and with greater force, so the pressure rises.pressure rises

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If the volume of the container stays constant & # of particles of gas stays constant Then pressure increases in direct proportion to the Kelvin temperature. How are temperature and pressure related?

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pressure of a gas is directly proportional to its Kelvin temperature. P α T If t then p How are temperature and pressure related?

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Devices to Measure Pressure barometer - instrument that measures the pressure exerted by the atmosphere. The height of the mercury column measures the pressure exerted by the atmosphere

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The Barometer ****remember atmospheric pressure decreases with altitude because the depth of air above you is less The standard atmosphere (atm) is defined as the pressure that supports a 760-mm column of mercury.

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Pressure Units Atmospheric pressure is the force per unit area that the gases in the atmosphere exert on the surface of Earth. The SI unit for measuring pressure is the pascal (Pa),

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Pressure Units Because the pascal is a small pressure unit, it is more convenient to use the kilopascal. 1 kilopascal (kPa) is equivalent to 1000 pascals. 1 atm = kPa

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The Gas Laws The gas laws apply to ideal gases, which are described by the kinetic theory

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Boyles Law: Pressure and Volume After performing many experiments with gases. Boyle had four findings. at constant temperatures, 1)If pressure increases then volume decreases 2) If pressure decreases then volume increases

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Boyles Law: Pressure and Volume Boyles law states that the pressure and volume of a gas at constant temperature are indirectly proportional.Boyles law Click box to view movie clip.

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Boyles Law In mathematical terms, this law is expressed as follows.

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P 1 = initial pressure V 1 = initial volume P 2 = ending pressure V 2 = ending volume

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Kinetic explanation of Boyles Law At a constant temperature, the pressure exerted by a gas depends on the frequency of collisions between gas particles and the container. If the same number of particles is squeezed into a smaller space (decreased volume), the frequency of collisions increases, thereby increasing the pressure.

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Graph of Boyles Law pressure vs volume

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Applying Boyles Law A sample of compressed methane has a volume of 648 mL at a pressure of 503 kPa. To what pressure would the methane have to be compressed in order to have a volume of 216 mL ? Examine the Boyles law equation. You need to find P 2, the new pressure, so solve the equation for P 2.

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Applying Boyles Law Substitute known values and solve.

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Charless Law: Temperature and Volume At constant pressure If the temperature is increased, if the volume is free to change, then The volume increases

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Charless Law Charless law Charless law states that the volume and temperature of a gas at constant pressure are directly proportional Click box to view movie clip.

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Kinetic explanation of Charless Law If the temperature is increased, average kinetic energy and particle movement increases and if volume is free to change it increases too

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Graph of Charless Law volume vs temperature

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Applying Charless Law A weather balloon contains 5.30 kL of helium gas when the temperature is 12°C. At what temperature will the balloons volume have increased to 6.00 kL? Start by converting the given temperature to kelvins.

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Applying Charless Law Next, solve the Charless law equation for the new temperature, T 2.

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Applying Charless Law Then, substitute the known values and compute the result. Finally, convert the Kelvin temperature back to Celsius. New Temperature = 323 – 273 = 50 o C

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GAY-LUSSACS LAW – pressure and temperature At constant volume If the temperature is increased, Then pressure increases P 1 = P 2 T 1 T 2

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GAY-LUSSACS LAW Gay- Lussacs law states that the temperature and pressure of a gas at constant volume are directly proportional

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Kinetic explanation of Gay-Lussacs Law If the temperature is increased, average kinetic energy and particle movement increases and collisions occur more frequently, thereby increasing pressure

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P 1 = P 2 T 1 T 2 Boyles Law Charless Law Gay-Lussacs Law

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Potato Chips are Very Good To Bite. Pressure constant – Charles Volume constant – Gay-Lussac Temperature constant – Boyle

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The Combined Gas Law The gas laws may be combined into a single law, called the combined gas law, that relates two sets of conditions of pressure, volume, and temperature by the following equation. With this equation, you can find the value of any one of the variables if you know the other five.

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Applying the Combined Gas Law A sample of nitrogen monoxide has a volume of 72.6 mL at a temperature of 16°C and a pressure of kPa. What volume will the sample occupy at 24°C and 99.3 kPa? Start by converting the temperatures to kelvins.

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Applying the Combined Gas Law Next, solve the combined gas law equation for the quantity to be determined, the new volume, V 2.

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Applying the Combined Gas Law Substitute the known quantities and compute V 2.

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STP = Standard Temperature & Pressure 0°Cand 1 atm STP

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Avogadros Principle Avogadros principle - equal volumes of gases at the same temperature and pressure contain the same number of particles. An extension of Avogadros principle is that one mole (6.02 x particles) of any gas at STP (standard temperature and pressure -0°C and 1.00 atm pressure) occupies a volume of 22.4 L.

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Applying Avogadros Principle What is the volume of 7.17 g of neon gas at 24°C and 1.05 atm? Start by converting the mass of neon to moles. The periodic table tells you that the atomic mass of neon is amu. Therefore, the molar mass of neon is g.

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Applying Avogadros Principle Next, determine the volume at STP of mol Ne. If you needed only the volume at STP, you could stop here. Finally, use the combined gas law equation to determine the volume of the neon at 24°C and 1.05 atm pressure. Gases: Basic Concepts Topic 13 Topic 13

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Applying Avogadros Principle Gases: Basic Concepts Topic 13 Topic 13

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Question 4 What pressure will be needed to reduce the volume of 77.4 L of helium at 98.0 kPa to a volume of 60.0 L? Basic Assessment Questions Topic 13 Topic 13

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Answer 126 kPa Basic Assessment Questions Topic 13 Topic 13

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Question 5 A sample of SO 2 gas has a volume of 1.16 L at a temperature of 23°C. At what temperature will the gas have a volume of 1.25 L? Basic Assessment Questions Topic 13 Topic 13

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Answer 46°C or 31.9 K Basic Assessment Questions Topic 13 Topic 13

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The End!

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