Equilibrium Constant

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# Equilibrium Constant - PowerPoint PPT Presentation

Equilibrium Constant. Example. H 2 + F 2  2HF

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### Equilibrium Constant

Example

H2 + F2 2HF

The equilibrium constant for the reaction above is found to be 2.1 x 103 at a specific temperature. At equilibrium, the concentrations of both hydrogen and fluorine are found to be 0.0045 M. What is the equilibrium concentration of hydrogen fluoride?

Example
• A mixture of 5.00 x 10-3 mole of H2 and 1.00 x 10-2 mole of I2 is placed in a 5.00L container and allowed to come to equilibrium. Analysis of the equilibrium mixture shows the concentration of HI is 1.87 x 10-3 M. Calculate the Kc at 448°C for this reaction.

H2 + I2 2HI

Example
• Sulfur trioxide decomposes at high temperatures in a sealed container as shown: 2SO3 2SO2 + O2 Initially the vessel is charged at 1000K with 6.09 x 10-3 M SO3. At equilibrium the SO3 concentration is 2.44 x 10-3 M. Calculate the Kc at 1000K.
Kc and Kp
• When concentration is expressed in M use Kc as the constant.
• When concentration is expressed in atm use Kp
• aA  cC + dD
• Kp = Pcc PDd / PAa
Example
• The reaction for the formation of nitrosyl chloride

2NO(g) + Cl2(g)  2NOCl(g)

was studied at 25°C. The pressures at equilibrium were found to be PNOCl= 1.2atm, PNO = 5.0x10-2atm, and PCl = .3atm. Calculate the Kp for this reaction.

Kp from Kc
• Kp = Kc (RT)n
• n – total coefficients of gaseous products minus total coefficients of gaseous reactants
• R = .0821 L atm/mol K
Example
• The Kc for the reaction N2 + 3H2 2NH3 is .105. Calculate the Kp at 472°C.
Solids and Liquids
• The concentrations of pure solids and liquids in a reaction does not really change
• They are not included in the equilibrium expression
Example
• Write the equilibrium expression for:

CO2(g) + H2(g)  CO(g) + H2O(l)

SnO2(s) + 2CO(g)  Sn(s) + 2CO2(g)