07_-_Chemical_Equilibrium

07_-_Chemical_Equilibrium - ChE 102: Chemistry for...

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Unformatted text preview: ChE 102: Chemistry for Engineers 15.1-15.7 Chemical Equilibrium 18.1-18.5 Solubility and Complex-Ion Equilibrium 07 - Chemical Equilibrium 2 Dynamic Equilibrium Continuous movement of particles from one phase to another Equilibrium can exist for both physical and chemical processes 07 - Chemical Equilibrium 3 Nature of Chemical Equilibrium Methanol is produced from syngas according to the following reversible reaction: CO ( g ) + 2 H 2 ( g ) CH 3 OH ( g ) CH 3 OH ( g ) CO ( g ) + 2 H 2 ( g ) When chemical equilibrium is reached, the concentrations of all reactants and products remain constant Chemical equilibrium is a dynamic process: Rate of forward reaction = Rate of reverse reaction Reaction does not stop 07 - Chemical Equilibrium 4 CO ( g ) + 2 H 2 ( g ) CH 3 OH ( g ) 07 - Chemical Equilibrium 5 07 - Chemical Equilibrium 6 Equilibrium Constant ( K c ) For the reaction: CO ( g ) + 2 H 2 ( g ) CH 3 OH( g ) the equilibrium constant is defined as: Using the values given in the Table: 2 2 3 ] ][ [ ] [ H CO OH CH K c = 5 . 14 ) 176 . )( 138 . ( ) 062 . ( ) 151 . )( 0753 . ( ) 0247 . ( ) 0822 . )( 0911 . ( ) 00892 . ( 2 2 2 = = = = c K The value of the equilibrium constant is constant at a given temperature 07 - Chemical Equilibrium 7 Chemical Equilibrium: Reversible & Spontaneous CO ( g ) + 2 H 2 ( g ) CH 3 OH ( g ) What happens if we add more CO ( g ) after chemical equilibrium is reached? [CO] > [CO] eq Rate of forward reaction > Rate of reverse reaction More CH 3 OH is formed [CH 3 OH] increases rate of reverse reaction increases CO and H 2 are consumed [CO] and [H 2 ] decrease rate of forward reaction decreases Finally, a new equilibrium is reached when the rate of the forward reaction equals the rate of the reverse reaction 07 - Chemical Equilibrium 8 Equilibrium Constant ( K c ) For the general reversible chemical reaction: a A + b B c C + d D The equilibrium constant is defined by the equation: K c is constant for a given temperature K c is independent of the initial concentration of reactants and products (path independent) K c has units of (concentration) d + c a b Large K c : products are present in higher concentration than reactants Small K c : products are present in lower concentration than reactants b a d c c B A D C K ] [ ] [ ] [ ] [ = 07 - Chemical Equilibrium 9 Equilibrium Constant ( K c) 07 - Chemical Equilibrium 10 2 SO 2 ( g ) + O 2 ( g ) 2 SO 3 ( g ) at 1000K 2 2 2 10 7 . 2 ] 027 . [ ] 054 . [ ] 146 . [ = = c K 2 2 2 10 8 . 2 ] 016 . [ ] 032 . [ ] 068 . [ = = c K ] [ ] [ ] [ 2 2 2 2 3 O SO SO K c = 07 - Chemical Equilibrium 11 Example 1 At a certain temperature, K c = 1.8 10 4 M-2 for the reaction N 2 (g) + 3 H 2 (g) 2 NH 3 (g)....
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This note was uploaded on 09/17/2011 for the course CHE 102 taught by Professor Simon during the Spring '08 term at Waterloo.

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07_-_Chemical_Equilibrium - ChE 102: Chemistry for...

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