# A over this temperature range what is the standard

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is in K. (a) Over this temperature range, what is the standard enthalpy of formation of GaN? [1 mark] (b) What does the coefficient of T in equation 1 represent? [2 marks] (c) At high temperatures, gallium nitride decomposes into its elements. Predict the temperature above which this would happen when GaN is kept in 1 bar of N 2 . [3 marks] (d) Above what temperature would GaN decompose into its elements if kept in 20 bar of N 2 ? Does the difference between your answers to this and the previous question agree with Le Chatelier’s principle? Explain briefly. [8 marks] Note: Gallium melts at 302.9 K and boils at 2477 K, so it is a liquid over the temperature range for which equation 1 is valid. Useful data k B = 1 . 380 650 3 × 10 - 23 J/K L = 6 . 022 142 0 × 10 23 mol - 1 R = 8 . 314 472 J K - 1 mol - 1 Standard thermodynamic data at 298.15 K Species Δ f H kJ mol - 1 Δ f G kJ mol - 1 C p,m J K - 1 mol - 1 H 2 S (g) - 20 . 50 - 33 . 33 34 . 20 1 K. T. Jacob and G. Rajitha, J. Cryst. Growth 311 , 3806 (2009). 2
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