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Math Help - taking logs

  1. #1
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    taking logs

    Hi All..

    I'm having some trouble trying take logs of this equation below..

     \frac{S_1}{S_2} = \frac{\exp{(-Q/RT_1)}}{\exp{(-Q/RT_2)}}

    From my solution to the answer when I have plugged in the values I get a minus value..when it should be positive. So I think I have not taken the logs properly..

    I'm trying to find Q Where all the others are known values.
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  2. #2
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    Hi

     \frac{S_1}{S_2} = \frac{e^{-\frac{Q}{RT_1}}}{e^{-\frac{Q}{RT_2}}}  = e^{-\frac{Q}{RT_1}}\,e^{\frac{Q}{RT_2}}   = e^{Q(\frac{1}{RT_2}-\frac{1}{RT_1})}

     Q(\frac{1}{RT_2}-\frac{1}{RT_1}) = ln\frac{S_1}{S_2}

     Q = \frac{1}{\frac{1}{RT_2}-\frac{1}{RT_1}}\,ln\frac{S_1}{S_2}
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  3. #3
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    Thank you for that

    yeah I can see where I went wrong.. what happens to the minus sign on the first line before the Q/RT2 ?
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  4. #4
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    is there a general rule or does it just cancel out ?
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  5. #5
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    a^{-n} is defined to be \frac{1}{a^n}

    If u = a^{-1}, then u^n is defined to be \frac{1}{u^{-n}} and the reverse statement is true.
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