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Secondary IV • 2yr.

I have a hard time understanding how why ° C is used in the thermal energy equation Q = m * c * delta T. In many chemistry exercises, we have to use Kelvin. Thank you


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Explanations (1)

  • Explanation from Alloprof

    Explanation from Alloprof

    This Explanation was submitted by a member of the Alloprof team.

    Team Alloprof • 2yr. edited September 2021


    Thank you for your question!

    A temperature variation can be calculated in Kelvin or in degrees Celsius. To convince yourself of this, let's take for example two temperatures \(T_1\) and \(T_2\) given in ° C. To convert them to Kelvin, we must add 273.15. The temperature variation \( \triangle T\) therefore gives:

    $$ \triangle T = T_1-T_2 $$ 

    $$ \triangle T = (T_1+273,15)-(T_2+273,15) $$

    By distributing the negative sign in the second part of the equation, we obtain:

    $$ \triangle T = T_1\color{red} {+273,15} \color{black} {-T_2} \color{red} {-273,15} $$

    We therefore notice that the 273.15 cancel each other out, which amounts to our starting equation.

    When the formula includes  \( \triangle T\) , you can use either temperatures in Kelvin or in degrees Celsius since we have just shown that:

    $$ \triangle T = T_1-T_2 = (T_1+273,15)-(T_2+273,15) $$

    If you have other questions, do not hesitate to ask them on our forums!

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