List the individual steps used in constructing a Born-Haber cycle for the formation of BaI \(_{2}\) from the elements. Which of the steps would you expect to be exothermic?

Short Answer

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To construct a Born-Haber cycle for the formation of BaI\(_{2}\) from the elements, follow these steps: 1. Sublimation of barium: \(Ba_{(s)} \rightarrow Ba_{(g)}\) (endothermic) 2. Bond dissociation of iodine: \(I_{2 (s)} \rightarrow 2I_{(g)}\) (endothermic) 3. Ionization of barium: \(Ba_{(g)} \rightarrow Ba^{2+}_{(g)} + 2e^{-}\) (endothermic) 4. Electron affinity of iodine: \(I_{(g)} + e^{-} \rightarrow I^{-}_{(g)}\) (exothermic) 5. Formation of BaI\(_{2}\): \(Ba^{2+}_{(g)} + 2I^{-}_{(g)} \rightarrow BaI_{2 (s)}\) (exothermic) The exothermic steps in the Born-Haber cycle are the electron affinity of iodine (Step 4) and the formation of the ionic compound BaI\(_{2}\) (Step 5).

Step by step solution

01

Sublimation of barium

Starting from the solid elements, barium and iodine, we first consider the sublimation of barium. The sublimation process involves converting a solid into a gas. This involves the absorption of heat, making it an endothermic process. \[Ba_{(s)} \rightarrow Ba_{(g)}\]
02

Breaking the iodine molecule

Next, we need to break the diatomic iodine molecule (I2) into individual iodine atoms. This process is called bond dissociation. As the bond between two iodine atoms needs to be broken, this step is also an endothermic process. \[I_{2 (s)} \rightarrow 2I_{(g)}\]
03

Ionization of barium

The third step involves ionizing gaseous barium to form a positively charged ion with the removal of two electrons. In this process, we are providing energy to remove the electrons, making it an endothermic process. \[Ba_{(g)} \rightarrow Ba^{2+}_{(g)} + 2e^{-}\]
04

Electron affinity of iodine

The fourth step involves adding an electron to the gaseous iodine atoms to form negatively charged iodine ions. This process is known as electron affinity. As energy is released during electron addition, this step is exothermic. \[I_{(g)} + e^{-} \rightarrow I^{-}_{(g)}\] Please note that it happens twice because there are two iodine atoms.
05

Formation of the ionic compound BaI\(_{2}\)

Finally, the gaseous ions come together to form the ionic compound BaI2. As the positive and negative ions come together, there will be attractive forces between them. This process leads to a decrease in potential energy, releasing energy, making it an exothermic process. \[Ba^{2+}_{(g)} + 2I^{-}_{(g)} \rightarrow BaI_{2 (s)}\] Now, let's summarize the steps and their characteristics: 1. Sublimation of barium: endothermic 2. Bond dissociation of iodine: endothermic 3. Ionization of barium: endothermic 4. Electron affinity of iodine: exothermic 5. Formation of BaI2: exothermic The exothermic steps in constructing the Born-Haber cycle for BaI2 are the electron affinity of iodine (Step 4) and the formation of the ionic compound BaI2 (Step 5).

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