Report Sheet Name Pre-Lab Questions [Ni(H0) ] + + 6 NHỮ[Ni(NH] + + H2O 1. Given the spontaneous chemical reaction shown above and the fact that the bond energy (AH) for one Ni-O bond is approximately ill/mol and one Ni-N bond is 392 kJ/mol, calculate the overall AHon of the reaction. Hint – think about the number of bonds being broken (endothermic) compared to the bonds that are formed (exothermic) 2. Is formation of Ni-N bonds from Ni-O bonds a favored process with respect to enthalpy? Explain your answer in terms of how it contributes to the overall AG 3. Based on the number of moles between the reactants and products, what would you predict for the Arx? 4. Given your answers to #2 and 3, what would you say is the main driving force that is leading to the above reaction being spontaneous? Page 49

5. Below are the structures of the ammonia derivatives ethylenediame (en) and diethylenetriamine (dien). Draw the structure of the octahedral Nia complexes with each of these ligands. (Hint – in both cases the compound will have six Ni-N bonds.] HAN NH2 HAN NH2 ethylenediamine (en) diethylenetriamine (dien) 6. The reaction to form the nickel(II) complex with ethylenediamine (en) is shown below. Would you predict this reaction to be spontaneous? Justify your answer by predicting the signs for the enthalpy and entropy for the reaction. [Hint – walk through the same process you did in pre-lab questions #1-4.] [Ni(NH3).]2+ + 3 en — [Ni(en)]2+ + 6 NH,

Experiment Thermodynamics: Entropy vs. Enthalpy OH, Background The formation of a Lewis Acid-Base complex occurs when you have a lone pair of electrons being donated to an electropositive ion or atom. Common examples are the Lewis Acid-Base complexes that most metal ions form in water, as shown here for nickel(II). In the case shown, the Lewis base (H2O) is donating a lone pair of electrons to the nickel(II) ion to form what is Höös called a “coordinate” covalent bond. These are covalent H, 0TH bonds where the two shared electrons come from the d ate same atom (in this case, the O-atom). INCHI The formation of a variety of Lewis Acid-Base complexes and their stability is very useful for understanding the concepts of spontaneity, enthalpy, and entropy. For example, addition of ammonia, NH3, to the [Ni(H20)6]2+ complex results in the spontaneous displacement of the water molecules and formation of a [Ni(NH).]2+ complex, as shown below. [Ni(H20).]2+ + 6 NH3 — [Ni(NH3).]2+ + 6H2O 0-H bonds weakened As you learned in lecture, the spontaneity of a chemical reaction can be predicted and explained through Gibbs Free Energy (AGrxn) and the equation below. AGran = AHX – TAS A spontaneous reaction can be entropy, enthalpy, or both entropy and enthalpy driven. In this lab, we will conduct a series of reactions, observe their spontaneity, then make predictions about the relative driving forces of the reactions.

Procedure Before beginning this experiment, complete the pre-lab questions on the Report Sheet. After you complete the pre-lab questions, obtain the following equipment. • Spot plate (be sure the wells are clean and numbered) Part A – Establishing Colors of the Compounds 1. Add around 5 drops of the Niso, solution to 4 wells numbered 1-4. This is the [Ni(H2O)** complex. Record the color of the [Ni(H.0).Je on your Report Sheet. 2. Add approximately 3 drops of NH, (in the form of NH OH) to well #2. This is the [Ni(NH3)6]e complex. Record the color on your Report Sheet. 3. Add approximately 3 drops of ethylenediamine (en) to well #3. This is the [Ni(en)]2+ complex. Record the color on your Report Sheet. 4. Add approximately 3 drops of diethyltriamine (dien) to well #4. This is the [Ni(dien)]2+ complex. Record the color on your Report Sheet. 5. You may want to keep these for wells for reference. Feel free to use a second spot plate for the remainder of the experiment if needed. Part B – Determining if Reactions are Spontaneous 6. Conduct the 12 reactions listed on your report sheet, recording the beginning color of the compound in the chemical reaction and ending color you observe. a) Observation of a distinct color change indicates the reaction was spontaneous. The lack of a color change may indicate the reaction is non-spontaneous, but only when a color change was an expected outcome. Indicate in the Data Table if the reaction is spontaneous, non-spontaneous, or if you were unable to determine the spontaneity of the reaction.

Part A – Establishing the Colors of the Compounds Data Table – Color of Compounds [Ni(H01] [Ni(NH3)4] [Ni(en)a} [Ni(dien)? Light Purple Green Blue Purple Part B – Chemical Reactions Reaction Well Chemical Reactions Reactant 1 Reactant 2 Starting Ending Color Color Spontaneous Reaction? byes, no, or unable to determine) Yes INHO) (NICHO) NHS en INI(HO) dien Yes Yes NO [N (NH4)2+ но INI(NH)«J? Yes en dien INI(NH) Green Blue Green | Purple Green Purple Blue Blue Blue Purple Blue Purple Purple Purple Purple / Purple Purple furple Light Light Purple perple [Ni(en)sp HO Yes NO NO Nilens NH Niſenlap dien Yes Na HO [Ni(diena] [Ni(dien op [Ni(dien)] NH Lignt role Purpleht NO en Light Light NO

Part C – Chemical Reaction Predictions Write a balanced chemical reaction for each of the 12 reactions listed above. For each reaction, predict the sign and spontaneity of the AHⓇ and As for each reaction, then predict the sign of the AG” of the reaction and the driving force for the spontaneous reactions. Finally, state if your prediction for the spontaneity of the chemical reaction matched your observations. Give a brief explanation if they didn’t match. Example for Reaction i [Ni(H.0).]. (aq) + 6 NH, (aq)- [Ni(NH3)6]2+ (aq) + 6 H.0 (aq) • AHº will be (-), because bonds are changing from less stable Ni-O to more stable Ni-N. • AS will be be close to zero, , because 7 moles on each side of reaction and no change in states. Overall I predict the reaction to be spontaneous and enthalpy driven. Based on the experimentally observed color change, the reaction was spontaneous, which matches the prediction.