Non STP ProblemsDirections
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MASS-Volume Problems
First Step: Balance the equation
2Mg(s) + O2(g) 2MgO(s)
Second Step: Find the grams/mole of the solids (using the periodic table)
2Mg(s) + O2(g) 2MgO(s)
2Mg(s) + O2(g) 2MgO(s)
Mass-volume problems (cont)
Fourth Step: Find moles by dividing the grams by the grams/mole
5g
0.208m
Fifth Step: Use the mole ratio to determine the moles of the other components
5g
0.208m 0.104m 0.208m
Mass-volume problems (cont)
Sixth Step: Multiply the other moles by their grams/mol or liters/mol
5g 2.32L 8.32g
2Mg(s) + O2(g) 2MgO(s)
0.208m 0.104m 0.208m
Why do we use 22.4 l/m?
To achieve the value of 22.4, you take any GAS find its molecular mass and multiply that number by 1 liter divided by the gas’s density. (located in the CRC handbook)
Ideal Gas Law
At STP Temp. = 273 K, Pressure = 101.325 KPA
V/n = (8.31)(273K)/(101.325 KPA)
V/n = 22.4 Liters/mole
Pv=nRT
V/n = (RT)/(P)
Find the Liters/mole if temp = 20 degrees C, and the pressure = 600 torrs
1) convert temp. to kelvin and pressure to KPa
20 C + 273 = 293 K
600torr x (1/760) x (101.325/1) =80 KPa
V/n = (8.31 x 293) / (80)
V/n = 30.4 L/M
Find mass-volume problem at non-stp
Repeat the same steps as in the example shown for STP
Except instead of using 22.4 L/m to find the liters you find the liters/mole (V/n), using the equation on the previous side.
example
Find the volume in Liters of oxygen and hydrogen when the pressure is at 167.97 Kpa and the temperature is 68 degrees C?
18g
V/N = RT/P
V/N = (8.31Kpa/mK)(341K)/(167.97KPa)
18g 16.87l 8.44l
2H2O(L) 2H2(g) + O2(g)
18g/m 16.87l/m 16.87l/m
1m 1m 0.5m
First Question:
If the temperature is in Celsius degrees and the pressure is in torrs. Temperature has to be in Celsius.
FALSE
TRUE
Oops, sorry that’s inncorrect
Because of the constant 8.31 Kpa/MoleKelvin, the temperature has to be in Kelvin and the pressure has to be in Kpa
Back to question 1
Correct, Now Question #2
If the pressure is 952 Torrs, what is the pressure in Kpa?
1.253 Kpa
126.923 Kpa
9.396 Kpa
Oops, sorry that’s inncorrect
To find Kpa from torrs divide by 760 and then multiply by 101.325
Go back to question 2
Correct, now question #3
Find the liters per mole when the temperature in 27 degrees Celsius and the pressure is 2.00 atm.
1.11 L/M
2.21 L/M
448.74 L/M
12.3 L/M
V/n = (RT)/P
Go back to question 3
Correct, Now question #4
Cu(s) + O2(g) CuO
When there is 50g of Cu and the temperature is 200 K and the pressure is 70 Kpa
8.31L
Did you remember to convert everything?
What about balance the equation?
Go Back to Question 4
Correct, now one last question
Find the volume of the oxygen and the nitrogen monoxide in the equation:
NO(g) + O2(g) NO2(g)
When there is 40.4 L of NO2 and the pressure is 800 torrs and the temperature is 50 degrees C
NO = 1.61 L
O2 = 20.2 L
NO = 1.59 L
O2 = 21.7 L
NO = 4.78 L
O2 = 24.4 L
NO = 56.98 L
O2 = 23.75 L
Make sure you convert everything necessary
Use the formula V/n = Rt/P
Go Back to Question 5
Works Cited
All work was provided by the notes taken in Mr. Wolfe’s class this year and in Chem 1.
Congratulations