From owner-chemistry[ AT ]ccl.net Tue Nov 4 18:24:01 2008 From: "Carlos Abraham Diaz cancerbero_85%%hotmail.com" To: CCL Subject: CCL: Question: arrhenius parameters with MOPAC Message-Id: <-38026-081104161952-31315-c/bQH1w0iisW/OAe3pgUlQ{:}server.ccl.net> X-Original-From: "Carlos Abraham Diaz" Date: Tue, 4 Nov 2008 16:19:48 -0500 Sent to CCL by: "Carlos Abraham Diaz" [cancerbero_85|hotmail.com] Hello. I need some help in the determination of the activation energy of this reaction: NH3 + H3PO4 ------> NH4H2PO4 + H2O ammonia phosphoric acid ammonium phosphate water It's a neutralization and exothermic reaction. And however a fast raction rate (i can't measure with standard equipment) I assume that is a elementary reaction. My questions are: IT'S POSSIBLE CALCULATE THE Ea WITH MOPAC IN A NORMAL PC? THERE IS NOT EXPERIMENTAL DATA ABOUT THIS REACTION? I have the heats of formation of reagents and products and i tried the bell-evans-polanyi correlation: Ea = E* + BHf And i found for a exothermic reaction that Ea = 40 + 0.25Hf But the result is a negative Ea. I don't have so much knowledge in computational chemistry and i only need the numeric valor of the Ea and/or the reference. Thank you. Carlos Abraham Diaz cancerbero_85===hotmail.com Ciudad Obregon, Sonora, Mexico.