Untitled - Kelly Walsh High School

Chemical Equilibria 211
Careful!
Don’t Forget!
Even when the same reaction is involved, the K may be different. This is because
the value of K changes with temperature. Always use the specified K even if it is
different from a similar example.
The first step in this, and most equilibria problems, should begin by writing the
equilibrium constant expression. In this case, the expression is:
[NH3 ]
Kc
2
[N2 ][H2 ] 3
The problem gives us: [N2] 2.00 M and [H2] 3.00 M. The next step is to
enter the given values into the equilibrium constant expression and rearrange
the expression to isolate the ammonia. Some people find it easier to reverse
these steps.
Kc 2.42 103 [NH3 ] 2
[2.00] [3.00] 3
[NH3 ] 2
[N2 ][H2 ] 3
[NH3] 2 2.42 103 [2.00] [3.00] 3 0.13068 (unrounded)
[NH3] 20.13068 0.361497 0.361 M NH3 Determine the value of K p for the following equilibrium: C(s) CO 2(g) K
2CO(g). At equilibrium, the carbon monoxide, CO, pressure is 1.22 atm and the
carbon dioxide, CO 2, pressure is 0.780 atm.
The first step in this, and most equilibria problems, should begin by writing the
equilibrium constant expression. In this case, the expression is for a K p so pressures
must be present. The expression is:
K p P2 CO
P CO2
Never include a solid in an equilibrium expression.