What is the Enthalpy and Internal Energy Change for a Thermochemical Reaction?

[peter444]

N_2_{(g)} + \frac{5}{2}O_2 \longrightarrow N_2O_5 + \mathfrm 533 kJ energy
533kJ energy is released as heat

We are given that 101.7g N2 , 102.97g O2 reacted. And this happens at T= 25C and P = 1atm

what is the delta H and delta U for this process per mol N2(g). And how much work is done by the surrounding?

Thanks
(H<- enthalpy , U<- internal energy of the system )

 

[chem_tr]

First of all, you need to write the coefficients correctly for the reaction.

N_2_{(g)} + \frac{5}{2}O_2 \longrightarrow N_2O_5 + \mathfrm 533 kJ energy

Then find the molar amounts of nitrogen and oxygen gas, by using N=14 and O=16 gram/mol.

If a thermal energy is given to the environment, then it is an exothermic reaction, thus \Delta H must be negative, and must have the dimension \frac {mol}{L}.

I have no idea what \displaystyle \Delta U is, so another friend will help you in the following days, I think.

 

[peter444]

First of all, you need to write the coefficients correctly for the reaction.

N_2_{(g)} + \frac{5}{2}O_2 \longrightarrow N_2O_5 + \mathfrm 533 kJ energy

Then find the molar amounts of nitrogen and oxygen gas, by using N=14 and O=16 gram/mol.

If a thermal energy is given to the environment, then it is an exothermic reaction, thus \Delta H must be negative, and must have the dimension \frac {mol}{L}.

I have no idea what \displaystyle \Delta U is, so another friend will help you in the following days, I think.

i found the number of moles for each gas, but we are not given the volume;As you say \Delta H = \frac {mol}{L}. And how is -533kJ usefull in this problem?
Thanks

 

[so-crates]

H = U + pv, so therefore \Delta H = \Delta U + \Delta (pV). First off, what is \Delta U?

You can't find \Delta (pV) directly. But for an ideal gas, what is pV equal to ?

 

[peter444]

For an ideal gas: PV=nRT
but how do I get U, (H=U+PV ) if i also need H

 

[so-crates]

I just realized something, you say the reaction occurs at 1 atm and 25 C, so it is both a constant temperature and constant pressure reaction ?

 

[wolfson_1123]

1 mole of a gas = 24 L (24dm^3)

So you have your mass, so just change that into number of moles, then multiply by 24 L. That will find your Volume.

 

[so-crates]

OK I don't know how you did on your test but

1) For an isothermal reaction for an ideal gas, \Delta U = C_v\Delta T and since presumably \Delta T = 0, it follows that \Delta U = 0

2) Under constant pressure, \Delta H = q. If you don't know what \Delta H is, go back and look at the thermodynamics section in your first-year chemistry book.

3) Well now since you know q and \Delta U , you can solve for w, right ?