Practice Problem 4
Calculate the rate at which HI disappears in the following reaction at the moment when I2 is being formed at a rate of 1.8 x 10-6 moles per liter per second:
2 HI(g) H2(g) + I2(g)
The balanced equation for the reaction shows that 2 moles of HI disappear for every mole of I2 formed. Thus, HI is consumed in this reaction twice as fast as I2 is formed:
Students sometimes get the wrong answer to this exercise because they become confused about whether the equation for the calculation should be written as:
You can avoid mistakes by checking to see whether your answer makes sense. The balanced equation states that 2 moles of HI are consumed for every mole of I2 produced. HI should therefore disappear (3.6 x 10-6 M/s) twice as fast as I2 is formed (1.8 x 10-6 M/s).