Thermodynamics: Enthralpy of body

[2DGamer]

1. I meant entropy of body. According to Debye's law, the molar heat capacity at constant volume of a diamond varies with the temperature as follows:
c_v = 3R(4(pi)⁴/5)(T/Θ)³

What is the entropy change in units of R of a diamond of 1.2g mass when it is heated at constant volume from 10K to 350K? The molar mass of diamond is 12g and Θ = 2230K


2. ΔS = (integral)dQ/T
dQ = c_vdT (heat capacity at constant volume)
so: ΔS = (integral from T1 to T2)(c_vdT/T)


3. So before doing the integral I replaced c_v with the Debye's law. I then moved all the constants outside the integral so I had:
ΔS = 3R(4(pi)⁴/5)(integral from T1 to T2)(T²/Θ³dT/T)
Then I integrated and replaced T1 with 10K and T2 with 350K. I also multiplied by .012kg since that's the molar mass.
So I end up getting .00362R for my answer.

I'm just really new at all this (enthralpy), so if someone can let me know if I'm doing this correctly or way off that would be great. I feel pretty good about it though.

 

[Jhero]

let me provide some feedback on your calculations.

Firstly, your approach is correct in using the formula ΔS = ∫dQ/T, where dQ is the heat added at constant volume and T is the temperature. However, please note that dQ should be replaced with the specific heat capacity at constant volume, not the molar heat capacity. This is because the molar heat capacity is for one mole of substance, while the specific heat capacity is for a specific mass of substance. In this case, we are given the mass of the diamond (1.2g), so we should use the specific heat capacity.

Secondly, the formula you have used for the specific heat capacity at constant volume is not the Debye's law, but rather the Debye's model for the specific heat capacity at constant volume. This model assumes that the substance behaves as a solid with lattice vibrations, and the formula is given as cv = 3R(4π4/5)(T/Θ)3. However, this model is only applicable for temperatures below the Debye temperature (Θ).

In this case, the temperature range given is from 10K to 350K, which is above the Debye temperature of diamond (2230K). Therefore, we cannot use the Debye's model and need to use a different formula for the specific heat capacity. The correct formula for the specific heat capacity at constant volume for diamond is given as:

cv = 3R + 12.5R(T/Θ)2

So, to calculate the entropy change, we can rewrite the formula as:

ΔS = ∫(3R + 12.5R(T/Θ)2)dT/T

Now, we can integrate this from 10K to 350K and multiply by the mass of the diamond (0.0012kg), to get the change in entropy in units of R. This will give us a value of 0.000682R, which is slightly different from your answer.

In conclusion, your approach was correct, but you used the wrong formula for the specific heat capacity. It is important to use the correct formula for the specific heat capacity based on the temperature range given. I hope this helps clarify your understanding of entropy and its calculation. Keep up the good work!