[laurence (OP)]

greetings everybody!

hope you're all doing alright. i have that question of thermodynamics which i couldn't figure it out how to solve. the text is originally turkish and i tried to translate it into english so, if there's a syntax error or something, please forgive me:) here it is:


a closed system consisted of a cylinder having a piston contains 400 kpa pressure and 0.5m^3 nitrogen gas at 27 c. then an electrical heater is started to work ,which is inside the system, and 2 amphere of current passes in 5 minutes which caused by a 120 v of resource. during the change of state, nitrogen gas expands and gives 2800 j of heat energy to the enviroment. by the ideal gas assuming, find the nitrogen gas' specific entalphy in kj/kmol at final state.

[Origin]

I assume this is a homework assignment so I don't think just giving the answer will help. 
Your first task is to find the moles in the sample:

a closed system consisted of a cylinder having a piston contains 400 kpa pressure and 0.5m^3 nitrogen gas at 27 c

That sentence gives you everything you need to calculate the moles using the ideal gas law.
You then should find the specific enthalpy at the starting temperature.  The only thing missing for that is the specific heat capacity for nitrogen.

then an electrical heater is started to work ,which is inside the system, and 2 amphere of current passes in 5 minutes which caused by a 120 v of resource. during the change of state, nitrogen gas expands and gives 2800 j of heat energy to the enviroment.

There seems to be a translation error.  I assume the 2800 j are added to the 'closed system' and not the environment outside the system.  So that information will allow you to easily calculate the added specific enthalpy added to the system.  So all you need to do is add the initial enthalpy to the added enthalpy to get the final enthalpy.

I believe this is the correct way to do this problem, if it is not, someone will quickly jump in to correct me.

[Eternal Student]

Hi.

   It doesn't look too bad actually @Origin .   The main thing is you've had a good go at trying to make sense out of the information.   I'm not certain what was being asked or how to advise, sorry.

   I think there may very well be some problems with the translation:
1.   

There seems to be a translation error.  I assume the 2800 j are added to the 'closed system' and not the environment outside the system.  So that information will allow you to easily calculate the added specific enthalpy added to the system.

   Maybe.   However, the heater device provided a lot more energy than that  (2 Amp x 120 V x 5 mins x 60 secs/min).     So, maybe in the original version of the question they really were implying that some of that energy,  2800 J to be precise, was passed to the environment.   Why?  - because they talk about expansion of the gas... see below....

2.   There is a description of pressure sustained by a piston.    One tends to imagine the main purpose of having the gas in a cylinder with a piston was just to keep that pressure on it.   There is also this broken sentence fragment....

during the change of state, nitrogen gas expands and gives 2800 j of heat energy to the enviroment. by the ideal gas assuming, find the nitrogen gas' specific entalphy in kj/kmol at final state.

    It seems possible that section was giving information like this.....     
(i)    The gas expands (after the heater device has delivered energy to it).
(ii)   You can assume the piston kept constant pressure.
(iii)   Under that expansion 2800 J  of energy was passed to the environment (it was work  pΔV done by the gas expanding).

     Anyway,  @laurence ,  if you are reading....   there are some problems with the translation of the question.   I can only guess what you were being asked to calculate:

1.      Were you asked just to calculate the  CHANGE in specific enthalpy  after the heater device was used for 5 minutes?
2.      There may be some difference in terminology.   "Specific enthalpy" is usually the enthalpy per unit mass and has units    KJ / Kg.     However, you seem to have been asked to find something in    KJ / mol    which is usually called the "Molar enthalpy"  (if it is per Kilo-Mole then I'm not sure it even has that name).
3.      If you really do need to determine the initial and final enthalpy,   then  were you given a standard reference sheet or told in an earlier part of the question what the  enthalpy of Nitrogen is at some convenient reference pressure and temperature?    If not, we need to  use the formula   H =  U  + PV  (with H = enthalpy;  U = internal energy; P= Pressure; V = Volume) and determine the initial enthalpy starting from U =0 at  0 Kelvin.  This means there could be 3 different specific heat capacities we need and 2  quantities of latent heat we need to include because Nitrogen will change   from  Solid --> Liquid   ---> Gas.   (If we could just start from a reference enthalpy at standard temperature and pressure it would be much quicker to calculate).

Best Wishes.