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A mixture of hydrogen and iodine in the mole ratio 1.5: 1 is held at 450 deg C. After equilibrium is reached for H2(g) + I2(g) <-> 2HI(g), the mole ratio of I2 to HI is found to be 1: 18. If 127 g of iodine were taken initially (atomic mass I = 127), calculate the equilibrium constant Kc.
- 54
- 18
- 36
- 27
Correct answer: 54
Solution
Working in relative moles (I2 initial = 1, H2 initial = 1.5), the ICE table gives I2 = 0.1, HI = 1.8, H2 = 0.6, so Kc = (1.8)²/(0.6*0.1) = 54; the absolute amount and volume cancel because the number of gas moles is equal on both sides.
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