# Chemical Equilibrium of Reaction's constant?

1. Feb 13, 2014

### Matriculator

I'm currently studying for a test and I'm having problem with this concept:

If I have 3 different Equilibrium constants for different reactions like Kc=103, Kc=1 and KC=10-4, which one's forward reaction is most favorable, and which one's reverse reaction is most favorable?

Maybe it's the way the question is stated but I have a good understanding of most of the things in this chapter, this one doesn't make sense at all. Can anyone please help? Thank you very much.

2. Feb 13, 2014

### Staff: Mentor

The equilibrium constant is the ratio of the kinetic rate constant for the forward reaction to the kinetic rate constant for the reverse reaction.

3. Feb 13, 2014

### Matriculator

Thank you for replying. I understand that part, but what I'm having a hard time with is how to determine from different constants which movement(forward or backward) will be favorable(or not so).

4. Feb 13, 2014

### Staff: Mentor

If K is high, then the forward reaction is favored over the reverse reaction. If K is low, then the reverse reaction is favored over the forward reaction.

5. Feb 13, 2014

### Matriculator

But why is this so- perhaps algebraically? My teacher told me something like this but I couldn't make out the reasoning behind it. Thank you.

6. Feb 14, 2014

### Staff: Mentor

Write the equilibrium constant for the reaction

A -> B

If it is higher than 1 - which substance is in the excess? Where does the equilibrium lie, on the left, or on the right?

And if it is lower than 1?

7. Feb 14, 2014

### Staff: Mentor

For the reaction that Borek wrote, the kinetic expression at equilibrium is:

kf[A]-kr=0

Now solve algebraically for the equilibrium constant /[A]. This should be in your textbook.

Chet