0:02 this is msjcam in this video i'll be
0:05 looking at the molar volume of a gas
0:08 the molar volume of a gas is the volume
0:11 occupied by one mole of an ideal gas
0:14 the molar volume must be stated at
0:16 specific conditions
0:17 in this video i'll be using the
0:20 conditions of stp
0:24 these are a temperature of 273 kelvin
0:27 and a pressure of 100 000 pascals
0:29 here we can see these values plugged
0:31 into the ideal gas equation
0:33 which has been rearranged to calculate
0:35 for volume
0:38 as we can see this gives us a volume of
0:40 0.0227 meters
0:43 cubed the molar volume can be determined
0:45 by dividing the volume by the amount in moles
0:46 moles
0:49 in this equation we have a volume of
0:51 0.0227 meters
0:54 cubed which is the volume occupied by
0:56 one mole of an ideal gas
0:58 so this gives us the molar volume of an
1:00 ideal gas
1:04 under conditions of stp which is
1:08 0.0227 meters cubed per mole
1:11 or 22.7 decimeters cubed
1:13 per mole in the previous slide we
1:16 defined the molar volume of a gas as the
1:18 volume occupied by one mole of an ideal gas
1:19 gas
1:22 under conditions of stp under these conditions
1:22 conditions
1:25 real gases such as oxygen hydrogen and chlorine
1:26 chlorine
1:29 behave almost the same as ideal gases
1:32 for example one mole of oxygen gas under
1:34 conditions of stp
1:37 will occupy a volume of 22.7 decimeters cubed
1:38 cubed
1:40 the same is true for one mole of
1:41 hydrogen gas
1:44 and one mole of chlorine gas
1:46 so we can now say that under conditions
1:48 of stp one mole of
1:52 any gas be it an ideal gas or a real gas
1:56 occupies a volume of 0.0227 meters cubed
2:00 which is more commonly given as 22.7
2:03 decimeters cubed
2:05 next we'll look at equations that can be
2:07 used to calculate either the volume
2:11 or the amount in moles of a gas
2:13 the first equation we look at is used to
2:15 calculate volume
2:16 to calculate the volume of a gas
2:18 multiply the amount of moles
2:21 by the molar volume an easy way to remember
2:22 remember
2:25 this equation is v equals n multiplied by
2:26 by
2:29 22.7 note that this equation will give
2:30 you the volume
2:33 in decimeters cubed the next equation is
2:36 used to calculate the amount in moles
2:38 to calculate the amount of moles divide
2:39 the volume
2:42 by the molar volume once again an easy
2:43 way to remember this equation
2:48 is n equals v divided by 22.7
2:51 in the first example we'll calculate the
2:53 volume in decimeters cubed
2:57 occupied by 0.250 moles of nitrogen gas
3:00 at stp the equation that we'll use is volume
3:00 volume
3:03 equals amount in moles multiplied by the
3:05 molar volume of a gas
3:08 so the volume is equal to 0.250
3:12 multiplied by 22.7 and this gives a
3:15 volume of 5.68 decimeters cubed
3:17 note that the unit of volume in the
3:19 answer is the same as that in the question
3:20 question
3:23 which is decimeters cubed the next
3:25 example is calculate the volume in
3:28 centimeters cubed occupied by
3:31 0.00619 moles of carbon dioxide
3:34 at stp so first we'll calculate the
3:36 volume in decimeters cubed and then
3:37 convert to
3:40 centimeters cubed to do this we multiply
3:41 the amount in moles
3:44 by the molar volume and this gives us 0.14
3:46 0.14
3:49 decimeters cubed because the question is
3:51 asking for the volume in centimeters cubed
3:51 cubed
3:53 the final step is to convert from
3:55 decimeters cubed to
3:58 centimeters cubed one decimeter cubed
4:01 is equal to 1000 centimeters cubed so we
4:03 multiply this volume in decimeters cubed
4:06 by one thousand and this gives a volume
4:07 of 141
4:11 centimeters cubed of carbon dioxide
4:13 in the next example we'll calculate the
4:16 amount of moles of nitrogen in a 0.742
4:19 decimeter cubed sample so we'll use this
4:20 equation which is
4:24 n equals v divided by 22.7
4:27 the volume of nitrogen is 0.742
4:29 decimeters cubed
4:31 which we then divide by the molar volume
4:33 of a gas at stp
4:35 and this gives us an amount of nitrogen
4:40 of 0.0327 moles
4:42 in the next example we'll calculate the
4:45 amount of moles of ch4 which is methane
4:48 in a 2.36 centimeter cube sample at
4:51 stp the first step in this calculation
4:53 is to convert the volume from
4:54 centimeters cubed to
4:58 decimeters cubed so 2.36 centimeters
5:01 cubed is equal to 2.36 times 10 to the
5:04 negative 3 decimeters cubed
5:06 we can then use the same equation as in
5:07 the previous slide which is
5:11 n equals v divided by 22.7
5:13 so as we just calculated the volume of
5:16 ch4 is 2.36 times 10 to the negative
5:18 three decimeters cubed
5:20 which we then divide by the molar volume
5:23 of a gas at stp
5:25 which gives us an amount of methane of 1.04
5:26 1.04
5:29 times 10 to the negative 4 moles
5:31 in the last example we'll determine the
5:34 volume of hydrogen in centimeters cubed
5:37 produced at stp when 2 grams of
5:39 magnesium is reacted with excess
5:40 hydrochloric acid
5:42 so here we have the balanced equation
5:44 for the reaction
5:46 magnesium reacts with hydrochloric acid
5:47 to produce
5:51 magnesium chloride and hydrogen gas
5:52 the first step is to determine the
5:55 amount in moles of magnesium
5:57 to do this we divide the mass of
5:59 magnesium by the molar mass
6:03 which gives us 0.0823 moles
6:05 we then use the balanced equation to
6:06 determine the ratio
6:10 of magnesium to hydrogen so from the
6:12 balanced equation we can see it's a 1 to
6:13 1 ratio
6:16 so this means that 0.0823 moles of magnesium
6:17 magnesium
6:20 will produce the same amount which is
6:22 0.0823 moles of
6:24 hydrogen so in the previous slide we
6:26 determine the amount of moles of hydrogen
6:27 hydrogen
6:29 that will be produced in the reaction
6:31 next we'll convert the amount in moles
6:33 to volume
6:35 we'll use the equation volume equals
6:36 amount in moles
6:40 multiplied by 22.7 so that's
6:44 0.0823 multiplied by 22.7
6:48 which gives a volume of 1.87 decimeters
6:50 cubed in the final step we'll convert
6:53 from decimeters cubed to centimeters cubed
6:54 cubed
6:57 so 1.87 decimeters cubed is equal to
6:59 1.87 times 10 to the 3
7:02 centimeters cubed so this is the volume
7:03 of hydrogen gas
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