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boraxlabnotes - Borax Lab Cliffs Notes The main idea of...

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Borax Lab Cliff’s Notes The main idea of this lab is to determine some thermodynamic parameters of the dissolution of borax in water. What this really means is we’re going to dissolve a chemical called borax (Na 2 [B 4 O 5 (OH) 4 ] 8H 2 O), which is really just a big ionic compound) in water and do some analysis that lets us talk about the energy involved in this reaction. You’ve had some exposure to a few thermodynamic terms, like enthalpy, but you need a little more background before you can do this lab and talk extensively about your results in a formal report. This is an attempt to briefly define these terms you’ll need and talk about the concepts involved to help you get a better grasp on the intricacies of this lab. This is by no means a comprehensive explanation; it’s just enough to help with the borax lab. Thermodynamics: Enthalpy—loosely, this is the energy of a chemical system; a change in enthalpy is associated with the difference in enthalpy (energy) of the reactants and products; a positive change in enthalpy indicates an endothermic process (absorbs heat/energy from surroundings), and a negative change indicates an exothermic process (releases heat/energy to surroundings); can associate enthalpy change to the difference in bond energies of the reactants and the products; a negative enthalpy change is “favorable”—decreases energy of the system, making it more stable Entropy—a measure of the disorder of a system; mathematically, this can be defined based on the number of arrangements your system can make (more arrangements=more disorder=higher entropy); chemically, the side of a chemical reaction with more gaseous species is often higher in entropy; in any process, the entropy of the universe must be increasing; a reaction with a negative change in entropy means the products are more ordered than the reactants (a positive change means the products are more disordered); a positive entropy change is “favorable”—increases entropy of the system Spontenaity—a spontaneous reaction is one that proceeds from reactants to products, as written, without needing added energy from the surroundings Free energy—the energy of a system available to do work You can’t predict the spontaneity of a reaction solely by its enthalpy change or entropy change. Endothermic reactions can spontaneously occur just as exothermic can, and some spontaneous reactions end in more ordered products while others end in more disordered. The combination of entropy and enthalpy, as well as the system temperature, are needed to fully predict if the reaction will proceed forward or not (to predict if it is favorable). Free
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energy (G) is a way to talk about all of these things at once. A negative free energy change indicates a spontaneous reaction (as written, the reaction will move forward). A positive free energy change indicates a reaction that
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