Heat needed to change temperature of hydrogen gas

[Kalie]

A rigid container holds 0.650 of hydrogen gas. How much heat is needed to change the temperature of the gas from 50 K to 100 K?
All right I know this is easy but for some reason I can't get the right answer what i have been doing is using the equation Q=nC_v(T_f-T_i)
Hydrogen gas is 1 g/mol
so n= .65 mol
C_v= 5/2 R= 20.775
because hydrogen gas is diatomic?
(T_f-T_i)= 100-50= 50
so putting it all together I get 675.188
which is wrong I made Hydrogen monotomic for the hay of it and got 405 J which is wrong too.
Please tell me what I am doing wrong...

 

[OlderDan]

A rigid container holds 0.650 of hydrogen gas. How much heat is needed to change the temperature of the gas from 50 K to 100 K?
All right I know this is easy but for some reason I can't get the right answer what i have been doing is using the equation Q=nC_v(T_f-T_i)
Hydrogen gas is 1 g/mol
so n= .65 mol
C_v= 5/2 R= 20.775
because hydrogen gas is diatomic?
(T_f-T_i)= 100-50= 50
so putting it all together I get 675.188
which is wrong I made Hydrogen monotomic for the hay of it and got 405 J which is wrong too.
Please tell me what I am doing wrong...

See the highlights in the quote. A contradiction?

 

[Kalie]

See the highlights in the quote. A contradiction?

But i also calculated it for monotomic too...

 

[OlderDan]

But i also calculated it for monotomic too...

Did you calculate it for diatomic using the correct mass?

 

[Kalie]

Did you calculate it for diatomic using the correct mass?

Oh!
But When I do that I get
.65/2 = .325
.325*20.775*50 = 337.6 which is still wrong

 

[Kalie]

nevermind monatomic at that temp