Why Does Charles' Law Give a Different Answer Without Converting to Kelvin?

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SUMMARY

The discussion centers on the application of Charles' Law, specifically the necessity of converting temperature to Kelvin for accurate calculations. Charles' Law states that the ratio of volume to temperature (V_1/T_1 = V_2/T_2) requires absolute temperature for validity. The difference arises because Kelvin and Celsius represent temperature differently; Kelvin is derived from Celsius by adding 273.15. Therefore, using Celsius directly in the formula leads to incorrect results, as the relationship does not allow for simple cancellation of terms.

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  • Understanding of Charles' Law and its formula (V_1/T_1 = V_2/T_2)
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MRCHEM
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why is the answer different if you didnt convert T into kelvin considering that
they have the same temp in actual process
 
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The same temperature? Yes, but Kelvin and celsius use different numbers to represent that temperature! Using different numbers in a formula typically gives different answers.

Oh, I see what you mean! Charles Law says that V_1/T_1= V_2/T_2 so V_1/V_2= T_1/T_2 and you are asking why the differences don't "cancel". They would IF Kelvin temperature were simply a multiple of celsius Temperature. If K= aC, then K_1/K_2= (aC_1)/(aC_2)= C_1/C_2. But they are not: Kelvin temperature is celsius temperature minus 273.15. That is K= C-a. K_1/K_2= (C_1- a)/(C_2-a) and we can't cancel.
 
And keep it then in Celsius, Fahrenheit, Reaumur, Beufort, Mercali, Richter or other scales ? Maybe it's probably Charles law was valid only when both the volume and the temperature are expressed in SI units, with T the absolute thermodynamical temperature measured in Kelvin.

Daniel.
 

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