How Do You Calculate the Change in Internal Energy for Hydrogen Gas?

[alexithymia916]

Homework Statement

One mole of hydrogen gas is heated from 278 K to 390 K at constant pressure. Hydrogen has a specific heat of 43.6 J/mol*K. The universal gas constant is 8.31451 J/K mol. Calculate the change in the internal energy of the gas. Answer in units of J

Homework Equations

Change in Internal energy = (1.5)nRT
n= number of moles
R= universal gas constant
T= change in temperature

The Attempt at a Solution

(1.5)(1 mol)(8.31451 J/k mol)(112 K)
=
1396.83768

what am i doing wrong??
the website i have to submit my homework to says it's incorrect...

 

[chaoseverlasting]

I think that's right... You may want to look at the significant figures though.

 

[alexithymia916]

noo def not
my teacher HATES significant digits, so we're just supposed to carry it out about 5 decimal places
grr i can't figure this one out :(