During the previous century, the Haber process was occasionally operated at pressures of $1000\ \text{atm}$ and above. Today, it is usually carried out at pressures below $100\ \text{atm}$. What is the reason for this change?
- AAn iron catalyst is used.
- BMaintaining the higher pressures is more expensive.
- CThe equilibrium yield of ammonia is increased at lower pressures.
- DThe rate of the reaction is increased at lower pressures.