[HusamEddin]

Hi there,
How can I calculate the velocity of a gas in terms of the unit:
erg/(mol.deg)
??

there was a question in my exam:
The velocity of 28 grams of N2 gas at 27ْC equals:
1- 0.7300 erg/mol.deg
2- 5160 erg/mol.deg
3- 73000 erg/mol.deg
4- 51600 erg/mol.deg

the correct answer was the fourth one
I tried to calculate it by the equation
v = √(3RT/M) ... and the answer was 516 m/s ...
or it is 51600 cm/s
but does cm/s equals erg/mol.deg ??

another need of help
when I used the equation v = √(3KT/m) ... it didn't give me the same answer as v = √(3RT/M) .. but in fact , it must be likely ... so why it came for me like that


please help 

[HusamEddin]

when I say "erg/mol.deg"
then I surely mean "erg/mol.K"
where K is Kelvin

[Borek]

Question doesn't make sense to me - erg/mol*K is not a unit of speed (or velocity). erg is a unit of energy.

[HusamEddin]

the catastrophe is that the person who made the question is a professor O_o

OK thanks for now ... but may you please answer my last question in the first post:

"when I used the equation v = √(3KT/m) ... it didn't give me the same answer as v = √(3RT/M) .. but in fact , it must be alike ... so why it came for me like that ?"



and thank you very much

[HusamEddin]

still waiting

[sjb]

the catastrophe is that the person who made the question is a professor O_o

OK thanks for now ... but may you please answer my last question in the first post:

"when I used the equation v = √(3KT/m) ... it didn't give me the same answer as v = √(3RT/M) .. but in fact , it must be alike ... so why it came for me like that ?"



and thank you very much

Can you show the figures you used?

[HusamEddin]

the catastrophe is that the person who made the question is a professor O_o

OK thanks for now ... but may you please answer my last question in the first post:

"when I used the equation v = √(3KT/m) ... it didn't give me the same answer as v = √(3RT/M) .. but in fact , it must be alike ... so why it came for me like that ?"



and thank you very much

Can you show the figures you used?

sure ... look:
v = √(3KT/m)
√3*300(K)*1.38*10^-23(Joul/K) / (28/1000)(Kg) = 6.66*10^-10 m/s
v = √(3RT/m)
√3*300(K)*8.314(Joul/mol.K) / (28/1000)(Kg/mol) = 516.948 m/s


!!!

[sjb]

m (little m), is not 28g. It is the mass of one molecule of dinitrogen

[HusamEddin]

28/1000/6.022*10^23

[HusamEddin]

finally it gave me the same result
then molecular mass means the mass of one molecule >>> but why do I see some sites write the unit of molecular mass as (g/mol) but not (g)

[sjb]

finally it gave me the same result
then molecular mass means the mass of one molecule >>> but why do I see some sites write the unit of molecular mass as (g/mol) but not (g)

In the same way as eggs can cost 10p each, or £1.20 per dozen. The /mol bit here means the mass per mole, or per 6.02...x10²³ particles

[HusamEddin]

finally it gave me the same result
then molecular mass means the mass of one molecule >>> but why do I see some sites write the unit of molecular mass as (g/mol) but not (g)

In the same way as eggs can cost 10p each, or £1.20 per dozen. The /mol bit here means the mass per mole, or per 6.02...x10²³ particles

but if the mass per mole and the mass per 6.02...x10²³ particles are the same ...
then the molecular mass equals the molar mass !