Second and Zero Order Units

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Second and Zero Order Units

Postby VivianaHF2L » Fri Mar 08, 2019 3:00 am

They are written differently with zero order having moles first and second order having Liters first. Therefore, do they have different units so they must be written in this order or do they have the same regardless of the order?

Kevin ODonnell 2B
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Joined: Fri Sep 28, 2018 12:24 am

Re: Second and Zero Order Units

Postby Kevin ODonnell 2B » Fri Mar 08, 2019 3:19 am

The units of kr depend on the overall order of the reaction and ensure that kr x (concentration)a has the same units as the rate, namely, concentration/time. Thus, when the concentration is expressed in moles per liter and the rate is expressed in mol*L-1*s-1, the units of kr are a follows: 1st order = s-1. 2nd order = L*mol-1*s-1. 3rd order L2*mol-2*s-1.

Griffin Carter 2I
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Joined: Wed Nov 14, 2018 12:23 am

Re: Second and Zero Order Units

Postby Griffin Carter 2I » Sat Mar 09, 2019 7:31 pm

Zero and second order k values have different units because of their relationship to the rate which is always mol/L/sec. So because rate = k for 0 order then the units are simply mol/l/s while Rate = k[A]^2 for a second order equation so the units for k will be L/mol/s to cancel out the mol^2/L^2 of the concentration.

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