1)A slightly bruised apple will rot extensively in about four days at room tempe

Question

1)A slightly bruised apple will rot extensively in about four days at room temperature (25oC). If it is kept in a refrigerator at 4oC, the same extent of rotting takes about fifteen days. How long would it take for a slightly bruised apple to rot on a hot summer day at 32.0 oC? 2)include a sketch: Magnesium oxide, MgO, has the same type of structure as NaCl (i.e. the anions form a face-centred cubic structure and the cations occupy octahedral sites in the lattice of anions). The density of magnesium oxide is 3.58 g/ cm3. Given that the radius of the O2- ion is about 140 pm in most oxides, calculate the radius of Mg2+, in pm. Your solution should include a sketch one face of the unit cell of MgO to show how the edge length of the unit cell is related to the ionic radii.

Explanation / Answer

1) k2 = 1/4 (rots 1/4 of the way per day) k1 = 1/16 (rots 1/16 of the way per day) R = 8.3144 J mol^-1 K^-1 T2 = 293 K T1 = 273 K ln(0.25/0.0625) = (Ea/R)[(T2-T1)/T1T2] = Ea x (2.5x10^-4/8.3144) 1.386 = Ea x 3x10^-5 Ea = 46098 J/mol Ea = 4.61x10^4 J/mol

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