Question

Answer the following short answer questions.

A) What feature of a reaction would ensure that its rate would respond to a pressure jump?

B) Compare and contrast the pre-equilibrium and steady state approximations.

C) Explain the role of the salt-bridge in an electrochemical cell.

Answer 1

B) Pre-equilibrium as the name implies is prior to any chemical transformations occurring.The assumption of a pre-equilibrium is that the step before the rate determining step (RDS) is fast in both directions compared to the rate of the RDS. This is essentially the simplest way to consider a mechanism, categorizing one step as "slow" and all others as (relatively) "fast."

Steady-state refers to a trick that chemists use to approximate the rate of elementary chemical steps in a reaction. The steady-state approximation (SSA) does not explicitly make this assumption. It allows the possibility that the reverse of the first reaction and the second reaction might have comparable rates. It is a more general approach. If you have discussed the SSA in class, then you have probably also discussed that it can reduce to several other simpler cases. For example, if k2 << k(-1), then you recover the rate law you would get by assuming a pre-equilibrium. A noteworthy feature of the SSA is that the simplification can also be brought about by concentrations being very high or very low.