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Pressure, temperature and volume relationships (w/ a constant amount of molecules

Pressure, temperature and volume relationships (w/ a constant amount of molecules. As pressure , the volume_____ Therefore, the relationship is ______________ As temperature , the volume _____ Therefore, the relationship is ______________ As temperature , the pressure _____

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Pressure, temperature and volume relationships (w/ a constant amount of molecules

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  1. Pressure, temperature and volume relationships (w/ a constant amount of molecules • As pressure , the volume_____ • Therefore, the relationship is ______________ • As temperature , the volume _____ • Therefore, the relationship is ______________ • As temperature , the pressure _____ • Therefore, the relationship is ______________ inverse direct direct

  2. Calculations: • Temp must be in Kelvin…why? • (Kelvin = degrees Celsius + 273) • STP = Standard Temperature and Pressure • Standard Temperature = 273 K (0 oC) • Standard Pressure = 1atm, 760 mmHg, 101.3 kPa

  3. So when you do your calculations… • Set up factor label to appropriately adjust the variable • Change in pressure if volume goes UP? • Pressure will go DOWN • Set up factor label problem so the factor DECREASES the pressure • e.g. In an open container, with a fixed amount of air particles and temperature, that has a pressure of 100.0 kPa and a volume of 1.5 L, what is the pressure if the volume is changed to 2.0 L?

  4. Change in volume if pressure goes DOWN? • Volume will go UP • Set up factor label so that the factor INCREASES the volume • In a open container, with a fixed amount of air particles and temperature, that has a pressure of 125.0 kPa and a volume of 5.0 L, what is the volume if the pressure is changed to 100.0 kPa?

  5. You can also combine 2 variables • In a open container, with a fixed amount of air particles, that has a pressure of 125.0 kPa, a temperature of 75K and a volume of 5.0 L, what is the new volume if the pressure is changed to 100.0 kPa and the temperature is changed to 150K?

  6. OR… • Conservation of energy tell us that what energy goes into a system will come out of the system. • What is the relationship between P and V? • What is the formula for the constant? • That tells us that the original conditions of pressure and volume will equal the new P and V conditions • P1V1=P2V2

  7. Apply this to P, T relationship and T,V relationships • P1/T1= P2/V2 • V1/T1 = V2/T2 • Combining them all together: • P1V1/T1=P2V2/T2

  8. Example #1 • In a closed container, w/ a fixed volume and amount of He particles, w/ a temperature of 25.0 degrees Celsius and a pressure of 70.0 kPa, what is the final temperature if the pressure is increased to 100.0 kPa?

  9. Example #2 • In an expandable (open) container, w/ a fixed pressure and amount of Ar particles, w/ a temperature of 50.0 degrees Celsius and a volume of 1500.0mL, what is the final temperature (in Celsius) if the volume is decreased to 500.0mL?

  10. Example #3 • In a closed container, w/ a fixed amount of Ar particles, w/ a temperature of -75.0 degrees Celsius and a pressure of 25.0 kPa, what is the final temperature (in Celsius) if the pressure is increased to 400.0 kPa?

  11. Ideal Gas Law • So far we have looked at how volume and temperature affect pressure. • One other variable we need to look at is the number of molecules or the moles of the gas • The more moles you have, the greater the pressure and the greater the volume (direct relationship) • e.g. pumping up a basketball

  12. Ideal Gas Law Equation • PV=nRT • P= pressure (in kPa) • V= volume (in L) • n= number of moles • R= ideal gas constant (8.31 L kPa/ K mol) • T= temperature (in K)

  13. Ideal Gas Law Equation • In an Ideal Gas Law problem, identify the knowns and the unknown, rearrange the equation to solve for the unknown then plug and chug • Ideal gas: assuming no volume or attractive/repulsive forces • Ideal gas law used when: moles or grams are part of the problem

  14. Avogadro’s Law • Nothing new: • 1 mol of any gas at STP= • 6.022 ee 23 molecules • 22.4 L • Mass = Molar mass • Use Molar Map

  15. Dalton’s Law • Total pressure of any combination of gases is equal to the pressure of EACH gas • P total = P gas 1 + P gas 2 + P gas 3…. • e.g. Lab this week, you calculated the pressure of hydrogen from the total pressure of the water vapor and of the pressure of the room • P atmosphere/room = P water vapor + P hydrogen gas

  16. Do you feel the pressure?

  17. Graham’s Law • How long does is it take for the smell of your rotting garbage to fill a room? • Gases will diffuse from areas of high pressure to low pressure, until uniform • It depends on how massive (g/mol) the gas particles are. • The more massive the particles, the slower they will move.

  18. Calculating rates of diffusion • Graham calculated EFFUSION, how quickly particles escaped from a container. • Diffusion is calculated the same way • Refer to page 353 of your text for the equation

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