What do the terms homogeneous and heterogeneous mean?
Using iron and its compounds as examples, describe the different ways homogeneous and heterogeneous catalysis act. Select one example of each, and for each example state the catalyst, say whether it is homogeneous or heterogeneous, write a balanced equation for the reaction, and outline the way in which the chosen catalyst lowers the activation energy.
The reaction involving $\text{SO}_2$, $\text{NO}_2$ and $\text{O}_2$ takes place in two stages: $\text{NO}_2 + \text{SO}_2 \rightarrow \text{NO} + \text{SO}_3\;\Delta H^\circ_1 = -88\,\text{kJ mol}^{-1}$ and $\text{NO} + \tfrac{1}{2}\text{O}_2 \rightarrow \text{NO}_2\;\Delta H^\circ_2 = -57\,\text{kJ mol}^{-1}$. The activation energy for the first stage, $E_{a1}$, is greater than that for the second stage, $E_{a2}$. Using the axes provided, draw a fully labelled reaction pathway diagram for this reaction, showing $E_{a1}$, $E_{a2}$, $\Delta H^\circ_1$ and $\Delta H^\circ_2$.