4C.3

[Ami_Pant_4G]

Calculate the final temperature and the change in enthalpy when 765 J of energy is transferred as heat to 0.820 mol Kr(g) at 298 K and 1.00 atm (a) at constant pressure; (b) at constant volume. Treat the gas as ideal.

Can someone please explain how to find the final temperature for both parts? Also how would I find enthalpy for part b? Thanks in advance.

[Bella Townsend]

Some equations you need to know for this equation is when you are calculating the Cpm for a molecule of one type of atom like an ideal gas you use q=n*5/2R*deltaT
when you are calculating the Cvm for a molecule of one type of atom like an ideal gas you use q=n*3/2R*deltaT

The rest is given to you

765=0.820 (5/2 * 8.314) (Tf - 298)
Tf=343 K

At constant pressure the enthalpy is equal to the heat so delta h= 765J

765=0.820 (3/2 * 8.314) (Tf - 298)
Tf=373 K

[MAC 4G]

The above post is correct in how you find delta T, I found that it was easier to delta T = q/nCv,m and then use the equation Tf = delta T + Ti. Then to find enthalpy of part b, you would use the equation delta H = q + nRdeltaT and plug in all the values you were given and the delta T value you found in part a (assuming you did it the way that I did solving for delta T before Tf)

[Matthew ILG 1L]

Is the change in enthalpy supposed to be much larger for part b than it is for part a?

[MAC 4G]

Is the change in enthalpy supposed to be much larger for part b than it is for part a?

Depends on what you define as much larger, assuming I calculated both correctly, part b is 510 J more than part a's enthalpy.

[DHavo_1E]

Hello,

Can I ask why for constant volume we do not get an answer for the change in enthalpy? Thank you

[Matthew Chan 1B]

Hello,

Can I ask why for constant volume we do not get an answer for the change in enthalpy? Thank you

This is because at a constant volume, q_v = of the system.

[DHavo_1E]

Hello,

Can I ask why for constant volume we do not get an answer for the change in enthalpy? Thank you

This is because at a constant volume, q_v = of the system.

Hello,

Can I ask that when you found qv=deltaV whether you used the equation q=U-w? Is the enthalpy equation: DeltaH=DeltaU+pDeltaV used only for constant pressure but not constant volume? Thank you!!