In the iodine clock reaction governed by the following four equations: IO3-(aq) + 3HSO3-(aq) -> I-(aq) + 3H+(aq) + 3SO42- (aq) 6H+(aq) + I-(aq) + IO3-(aq) -> I2(aq) + 3H2O(l) I2(aq) + HSO3-(aq) + H2O(l) -> 2I-(aq) +SO42- (aq) + 2H+(aq) I2(aq) + starch -> blue/black colored complex What is the rate of reaction equal to, if the time taken for the blue-black complex to appear was measured?

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In the iodine clock reaction, the production of iodine, I-(aq) is the slowest step and therefore rate determining. The following steps are almost instantaneous. This means that a direct relationship can be drawn between the time for the chemical process of the first step and the time it takes for...

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In the iodine clock reaction, the production of iodine, I-(aq) is the slowest step and therefore rate determining. The following steps are almost instantaneous. This means that a direct relationship can be drawn between the time for the chemical process of the first step and the time it takes for the product to form.

Also, properly balanced, the byproduct of these reaction steps is 2IO3-(aq) + 2HSO3-(aq) -> 2SO42- (aq) + 2H2O(l), meaning step 1 is balances as: IO3-(aq) + HSO3-(aq) -> I-(aq) + 3H+(aq) + SO42- (aq)

Therefore, the full equation is:

1. IO3-(aq) + HSO3-(aq) -> I-(aq) + 3H+(aq) + SO42- (aq) (slow)

2. 6H+(aq) + I-(aq) + IO3-(aq) -> I2(aq) + 3H2O(l) (fast)

3. I2(aq) + HSO3-(aq) + H2O(l) -> 2I-(aq) +SO42- (aq) + 2H+(aq) (fast)

byproduct: 2IO3-(aq) + 4HSO3-(aq) -> 4SO42- (aq) + 2H2O(l)

4. I2(aq) + starch -> blue/black coloured complex

The rate of the reaction is determined by the concentrations input to step 1: IO3-(aq) + HSO3-(aq) and can be measured by time for the blue/black complex to form. So, the rate equation directly relates the two to determine the rate constant, k. Because the constant for both IO3-(aq) and HSO3-(aq) is 1, their concentrations are only raised to a power of 1

1/time for the blue/black complex to form (in seconds)= k[IO3-]^1[HSO3-]^1

This is a second order reaction because the exponents 1 + 1 = 2

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