When to convert into Kelvins by adding 273.15?

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Suk Jin Song 3L
Posts: 11
Joined: Tue Nov 17, 2015 3:00 am

When to convert into Kelvins by adding 273.15?

Postby Suk Jin Song 3L » Sun Feb 21, 2016 11:24 pm

So I am kinda confused on when I need to convert Celsius into Kelvin by adding 273.15.

For example, on Q2 of Midterm, I converted the temperatures listed into Kelvin by adding 273.15 but according to the answer key, the answers could be switched from Celsius to Kelvin without any adding (-70C = -70K).

I remember always adding 273.15 to Celsius to convert them when I solved problems so I wanted to know when I need to add 273.15 and when not so I do not repeat the same mistakes.

I believe this question has a pretty easy answer that only I don't know so I would really appreciate it if I can get an answer.

Monica Hana 2G
Posts: 19
Joined: Fri Sep 25, 2015 3:00 am

Re: When to convert into Kelvins by adding 273.15?

Postby Monica Hana 2G » Mon Feb 22, 2016 12:01 am

In this part of the question, it doesn't matter whether you are using Celsius or Kelvin because you are just taking the difference between the two temperatures. The change in temperature measured is ∆Ta = −45°C − 25°C = −70°C = -70 K on the solutions page. The change in temperature can also be written as (-45+273.15K)-(25+273.15K)=-70K. Because we are taking the change in temperature (final-initial), the 273.15 conversion factor cancels out, leaving you with the same CHANGE in temperature in Celsius and in Kelvin.

To convert from Celsius to Kelvin you always add 273.15. But for changes in temperature, it doesn't really matter, as long as you are using the same units for both the final and initial temperatures.

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