Question

At a certain temperature, the equilibrium constant for the following chemical equation is 3.00. At this temperature, calculate the number of moles of NO2(g) that must be added to 2.20 mol of SO2(g) in order to form 1.00 mol of SO3(g) at equilibrium. NO2 + SO2 -----------> SO3 + NO

Answer 1

The equilibrium constant of 3.0 = (moles SO3) * (moles NO) / [(moles SO2) * (moles NO2)]

The final moles of SO3 at equilibrium is to be 1.0 moles per the question. Since the products on the right hand side both have 1 in front of them, if you have 1.0 moles of SO₃, you must have 1.0 moles NO.

If you made 1.0 moles of SO₃ and NO, you needed to use 1.0 moles of SO₂ based on the equation. Since you had 2.20 moles initially, the final number of moles is 2.20 - 1.0 = 1.20 moles

As you add NO₂, 1.0 moles will react (from the reaction and you first need to work out how much additional NO2 is left over. Call that X moles.

3.0 = 1.0 * 1.0 / (X * 1.20). X = 0.2777 moles. So, since 1.0 moles NO₂ reacted with 1.0 moles of SO2 to make the 1.0 moles of the products, you must have added 1.0 + 0.2777 moles = 1.2777 moles.