# Rate Law

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I am trying to use the rate law attached in GWB react. I tried to define a custom rate law and wrote a script. However, calculated rate is not correct and does not change through time. I would be happy if you could help me with this. The script I wrote is below. Here is the publication I used for rate law https://pubs.usgs.gov/of/2004/1068/ . I would also be happy if you could let me know if there is any way to put three different k and E values without defining a custom rate law.

Thank you! LET kacid = 5.012 * 10^(-1)   * 10^(-4)
LET kneut = 1.549 * 10^(-6)  * 10^(-4)
LET kbase = 3.311 * 10^(-4)  * 10^(-4)
LET Eacid = 14.4    * 10^(3)
LET Eneut = 23.5   * 10^(3)
LET Ebase = 35.4   * 10^(3)
LET nacid = 1
LET nbase = 1
LET m1 = 1
LET m2 = 1
LET m3 = 1

x = kacid * EXP ((-Eacid / 8.314) * ((1/TK)-(1/298.15))) * (activity("H+")^(nacid)) * (1-(QoverK)^(m1))^(m1)
y = kneut * EXP ((-Eneut / 8.314) * ((1/TK)-(1/298.15))) * (1-(QoverK)^(m2))^(m2)
z = kbase * EXP ((-Ebase / 8.314) * ((1/TK)-(1/298.15))) * (activity("H+")^(nbase)) * (1-(QoverK)^(m3))^(m3)
rate = surface * (x + y + z)

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Hello Ozan,

I think the problem with your script is that you don’t have a return statement at the end. Can you try again with the statement

“RETURN rate “

at the bottom? For more examples, please refer to section 5.2 Rate law scripts in the Reaction Modeling Guide. If you would like for someone to take a closer look at the issue, please attach your model input file and the basic script file.

If you want to prescribe different k and E values in the same rate law, then you would need to implement a custom rate law. The built in format will only allow one value of each.

Hope this helps,

Jia Wang

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Thank you! RETURN worked!

Ozan

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