Laney CollegeCHEM 1BExperiment_17_-_Chem_1B

Document Content and Description Below

17 Thermodynamics of Borax Solubility Introduction In this experiment, you will determine the values of ∆H° and ∆S° for the reaction which occurs when borax (sodium tetraborate octahydrate)... dissolves in water. In previous experiments, you have determined ∆H° values directly, by measuring temperature changes when the reaction occurred. However, in many cases, this technique is not practicable. For example, the reaction may not go to completion, or it may give off such a small amount of heat that the temperature change is too small to measure. In addition, there is no direct method for measuring ∆S° for a reaction. It is therefore useful to be able to determine ∆H° and ∆S° indirectly, by using their relationship to the equilibrium constant of a reaction. The equilibrium constant of any reaction can be related to the free energy change of the reaction: ∆G° = –RT ln K The free energy change is also related to the enthalpy and entropy changes during the reaction: ∆G° = ∆H° – T∆S° Combining these two equations gives the general relationship between K, ∆H°, and ∆S°: –RT ln K = ∆H° – T∆S° Dividing both sides by –RT gives a particularly useful form of this relationship: ln K = – !H° R 1 T "# $% + !S° R This represents a linear equation of the form y = mx + b. In this case, y = ln K and x = 1/T; a plot of ln K against 1/T will therefore be linear. In addition, the slope of this line (m) will equal –(∆H°/R), and its y-intercept (b) will equal (∆S°/R). It is therefor [Show More]

Last updated: 1 year ago

Preview 1 out of 6 pages