Aflask is filled with pcl5 to a pressure of 2.00 atm at 300°c and allowed to come to equilibrium according to the reaction: pcl5(g) ⇄ pcl3(g) + cl2(g) analysis shows the total pressure in the flask at equilibrium is 3.96 atm. calculate the equilibrium constant kp for the reaction.

96.04

Explanation:

Kp is defined for any reaction as:

aA(g) +bB(g) ⇌ cC(g) +dD(g)

For the reaction:

Kp is:

P in the equation is the partial pressure for each specie in the equilibrium.

We know the total pressure for the system at the beginning is 2 atm. We can say that at the beginning we have just so the total pressure for the system is also the partial pressure for  

In the equilibrium we have the three species , and so now we need to estimate the partial pressure for each specie.  

We know that the total pressure for the system in the equilibrium is 3.96 atm. The total pressure is equal to the sum of the partial pressure of each component in the mix as:

Until we reach the equilibrium it’s been used to produce and . We can call (x) the among of   that reacted until the system reach the equilibrium so in the equilibrium will be

When reviewing the molar ratio in the reaction we see that it is 1: 1 so the amount of that reacted will be equal to the amount of and produced.

                           PCl5      Cl2                PCl3

Initial             2 atm          0 atm       0 atm  

Equilibrium      (2 atm - x)X atm       X atm

Using the equation for total pressure:

solving we get that x = 1.96 atm.

This is the partial pressure for and in the equilibrium  

For each component we have:

So

it's c. elements are placed in rows based on how may valencies electrons have.