Slide 1. Equilibrium. Slide 2. Equilibrium Constant Kp. Because gas pressures are easily measured, equilibrium equations for gas-phase reactions are often written as partial pressures rather than molarity concentrations.
Equilibrium Constant Kp
** Just a little note with the last slide…The equilibrium equations for Kp and Kc
have the same form except that the expression for Kp contains partial pressures instead of molar concentrations.
** For Kp as with Kc the units are omitted.
It can be shown that the values of Kp and Kc for a general gas-phase reaction are related by the equation:
For the reaction aA + bB cC + dD
Kp = Kc(RT)∆n
R = the gas constant 0.0821 L∙atm/K∙mol
T = absolute temperature in kelvin
∆n = is the sum of the coefficients of the gaseous reactions : for the above reaction (c+d) –(a+b)
For the decomposition of 1 mol of N2O4 to 2 mol NO2, ∆n = 2-1=1 and Kp=Kc(RT)1
H2(g) + I2(g) 2HI
For the reaction of 1 mol of hydrogen with 1 mol of iodine to give 2 mol of hydrogen iodine. ∆n= 2-(1+1) = 0 and
Kp=Kc(RT)0 or Kp = Kc
The Reaction Quotient
What Q tells us