Chemistry help!!! A-LEVEL
Hello, I know its only 1 mark but I don't get this question. Any help would be much appreciated!
(edited 11 months ago)
Original post by skyeforster15
Hello, I know its only 1 mark but I don't get this question. Any help would be much appreciated!
Did you have convert the unit for the volume from cm³ to m³ or anything else in your calculation forgotten?
@5hyl33n You are an expert for chemistry A levels, maybe you can see what went wrong! please help, if you can.
Original post by skyeforster15
Hello, I know its only 1 mark but I don't get this question. Any help would be much appreciated!
The volume of a sample of gas at 298 K and 100 kPa is (80 + 40 + 100) cm3.
The volume of the same sample of gas at (273 - 50) K and "x" kPa is 50 cm3.
Can you use pV=nRT to find "x"?
Original post by Kallisto
Did you have convert the unit for the volume from cm³ to m³ or anything else in your calculation forgotten?
@5hyl33n You are an expert for chemistry A levels, maybe you can see what went wrong! please help, if you can.
@5hyl33n You are an expert for chemistry A levels, maybe you can see what went wrong! please help, if you can.
Yes, I did all of that.
Original post by thomas.rhett
The volume of a sample of gas at 298 K and 100 kPa is (80 + 40 + 100) cm3.
The volume of the same sample of gas at (273 - 50) K and "x" kPa is 50 cm3.
Can you use pV=nRT to find "x"?
The volume of the same sample of gas at (273 - 50) K and "x" kPa is 50 cm3.
Can you use pV=nRT to find "x"?
I thought it meant -50 degrees Celsius not 273-50. I think this is where I went wrong.
(edited 11 months ago)
Original post by thomas.rhett
The volume of a sample of gas at 298 K and 100 kPa is (80 + 40 + 100) cm3.
The volume of the same sample of gas at (273 - 50) K and "x" kPa is 50 cm3.
Can you use pV=nRT to find "x"?
The volume of the same sample of gas at (273 - 50) K and "x" kPa is 50 cm3.
Can you use pV=nRT to find "x"?
I keep getting 330KPa. But there is no option for 330KPa only 329KPa.
(edited 11 months ago)
if you work out the number of moles in the original volume:
n = pV/RT
n = (100000*(80+40+100)/1,000,000)/(8.31*298) = 8.88393... x 10^-3 [use this exact value in your calculator with the ANS button for the next stage]
the moles doesn't change, so now just plug in your moles into the new volume
p= nRT/V
p = ((8.88x10^-3) * 8.31 * (-50+273)) / (50/1,000,000)
[also, don't round the moles. i'm writing 8.88 here but in my calculator i put the full value]
p = 329261 Pa
p = 329.261 kPa
p = 329 kPa (3sf)
n = pV/RT
n = (100000*(80+40+100)/1,000,000)/(8.31*298) = 8.88393... x 10^-3 [use this exact value in your calculator with the ANS button for the next stage]
the moles doesn't change, so now just plug in your moles into the new volume
p= nRT/V
p = ((8.88x10^-3) * 8.31 * (-50+273)) / (50/1,000,000)
[also, don't round the moles. i'm writing 8.88 here but in my calculator i put the full value]
p = 329261 Pa
p = 329.261 kPa
p = 329 kPa (3sf)
(edited 11 months ago)
Original post by skyeforster15
I keep getting 330KPa. But there is no option for 330KPa only 329KPa.
(100 kPa)(80 + 40 + 100 cm3) / (298 K) = (x kPa)(50 cm3) / (223 K) gives 329.3 kPa for x.
Original post by thomas.rhett
The volume of a sample of gas at 298 K and 100 kPa is (80 + 40 + 100) cm3.
The volume of the same sample of gas at (273 - 50) K and "x" kPa is 50 cm3.
Can you use pV=nRT to find "x"?
The volume of the same sample of gas at (273 - 50) K and "x" kPa is 50 cm3.
Can you use pV=nRT to find "x"?
Good job! I did not realized the conversion from °C to K. That makes the difference.
Original post by GhostHawk
if you work out the number of moles in the original volume:
n = pV/RT
n = (100000*(80+40+100)/1,000,000)/(8.31*298) = 8.88393... x 10^-3 [use this exact value in your calculator with the ANS button for the next stage]
the moles doesn't change, so now just plug in your moles into the new volume
p= nRT/V
p = ((8.88x10^-3) * 8.31 * (-50+273)) / (50/1,000,000)
[also, don't round the moles. i'm writing 8.88 here but in my calculator i put the full value]
p = 329261 Pa
p = 329.261 kPa
p = 329 kPa (3sf)
n = pV/RT
n = (100000*(80+40+100)/1,000,000)/(8.31*298) = 8.88393... x 10^-3 [use this exact value in your calculator with the ANS button for the next stage]
the moles doesn't change, so now just plug in your moles into the new volume
p= nRT/V
p = ((8.88x10^-3) * 8.31 * (-50+273)) / (50/1,000,000)
[also, don't round the moles. i'm writing 8.88 here but in my calculator i put the full value]
p = 329261 Pa
p = 329.261 kPa
p = 329 kPa (3sf)
Yes, that is very strange because I did do all that and got 230KPa but I types it in again and got 329KPa so it may have been due to a rounding error.
Easiest and quickest way uses
Pressure1 * Volume1/Temperature1 = Pressure2 * Volume2/Temperature2
You don’t have to change any units
So
100*220/298 = x * 50/223
So
x = 329
Pressure1 * Volume1/Temperature1 = Pressure2 * Volume2/Temperature2
You don’t have to change any units
So
100*220/298 = x * 50/223
So
x = 329
(edited 11 months ago)
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