Question 8.31

[Krupa Prajapati]

Hi! I was looking at question 8.31 in the textbook and I was confused because for calculating both Cpm and Cvm the book used the R value 8.31 J/mol*K but uses the temperature change in degrees Celsius. Why is there such a discrepancy? Thanks!

[Kyra LeRoy 1E]

Because getting from Celsius to Kelvin is just adding 273.15, the difference between T2 and T1 in Celsius is going to be just the same as between T2 and T1 in Kelvin.

For example:
If the initial temp is 20 degrees Celsius, that is 293.15 K.
If the final temp is 40 degrees Celsius, that is 313.15 K.
So:
For Celcius, delta T= 40-20 = 20
For Kelvin, delta T= 313.15-293.15 = 20

[Xin He 2L]

Since we're adding 273 to both the initial and final value of temperature, it doesn't matter if we use celsius or kelvin.

[Ashley Macabasco 2K]

The temperature change could be calculated either way using Kelvin or Celsius because regardless of which unit you use, the difference between the two temperatures will be the same.

[Warda Sahib 2J]

You can use either because adding 273 won't make a difference.

[Kayla Tchorz-Dis 1F]

Since you add 273 to both values, it would not interfere with the delta T value.

[404995677]

If you do the caculation, the change of Celcius and the change in Kelvin will be the same.

[204932558]

Kelvin = 273 + Degree Celcius. So it doesn't matter if you use either since the temperature difference is the same for both units.