10. When fluorine and solid iodine are heated to high temperatures, the iodine s
ID: 865881 • Letter: 1
Question
10. When fluorine and solid iodine are heated to high temperatures, the iodine sublimes and gaseous iodine heptafluoride forms. If 350.0 torr of fluorine gas and 2.50 g of solid iodine are put into a 2.50 L container at 250.0 K and the container is heated to 550.0 K, what is the final, total pressure? What is the partial pressure of iodine gas? Questions to Consider: (1) Do you have to find a limiting reactant? (2) How will you use the stoichiometric coefficients to find the total number of moles and thus the total pressure after the reaction ends? (3) What is the relationship between the final partial pressure of iodine gas and the final total pressure (or between the final number of moles of iodine and its partial pressure)?Explanation / Answer
7F2(g) + I2(g) ---------------> 2IF7(g)
Given, 350.0 torr of F2 gas.
Pressure of gas = 350.0 / 760.0 = 0.46 atm.
Pressure of gas at 550 K, then we use the equation P1/T1 = P2 / T2 => 0.46 / 250.0 = P2 / 550.0
=> P2 = 1.012 atm.
Pressure of F2(g) at 550.0 K is 1.012 atm
Now, let us find moles of F2(g) at 550.0 K using the equation PV = nRT
1.012 x 2.50 = n x 0.0821 x 550.0
=> n = 0.056 mol
Thus, moles of F2(g) = 0.056 mol
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Given, 2.50 g of I2. Let us find moles of Iodine.
Moles = Mass / Molar mass = 2.50 / 253.8 = 0.0098 mol
In order to find the limiting reactant, the moles of each reactant are to be divided by their respective stoichiometric coefficients. Thus,
F2 = 0.056 / 7 = 0.008 mol
I2 = 0.0098 /1 = 0.0098 mol
As the moles of F2 are less than the moles of I2, the limiting reactant is F2 gas.
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From the chemical equation, 7 mol of F2 gives two moles of IF7.
Thus, 0.056 mol of F2 gives 0.016 mol of IF7.
The final pressure requires total number of moles.
Total number of moles = Moles of product + Moles of reactant remaining.
Moles of product = 0.016 mol IF7
Moles of reactant left over = 0.0098 - 0.008 = 0.0018 mol of I2
Total = 0.0178 mol
Using PV = nRT
P = (0.0178 x 0.0821 x 550) / 2.50 = 0.322 atm
Thus, Final, total pressure = 0.322 atm.
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Partial pressure of Iodine => P = (0.0018 x 0.0821 x 550) / 2.50 = 0.0325 atm
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