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 ______________ direct inverse

Calculations: Temp must be in Kelvin…why? –(Kelvin = degrees Celsius + 273) STP = Standard Temperature and Pressure –Standard Temperature = 273 K (0 o C) –Standard Pressure = 1atm, 760 mmHg, kPa

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 kPa and a volume of 1.5 L, what is the pressure if the volume is changed to 2.0 L?

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 kPa and a volume of 5.0 L, what is the volume if the pressure is changed to kPa?

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

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 P 1 V 1 =P 2 V 2

Apply this to P, T relationship and T,V relationships P 1 /T 1 = P 2 /V 2 V 1 /T 1 = V 2 /T 2 Combining them all together: –P 1 V 1 /T 1 =P 2 V 2 /T 2

–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 kPa?

–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 mL, what is the final temperature (in Celsius) if the volume is decreased to 500.0mL?

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

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

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)

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

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

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

Do you feel the pressure?

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.

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