Midterm Review-ChemicalEqul

Midterm Review-ChemicalEqul - Chemistry 1C Page 1 of 8...

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Chemistry 1C Page 1 of 8 Midterm Review: Chemical Equilibrium Equilibrium is a state in which there are no observable changes as time goes by. Physical Equilibrium is equilibrium between two phases of the same substance. Ex. H 2 O ( ) Ù H 2 O (s) Chemical Equilibrium deals with reactions that maintain constant concentrations of products and reactants when the rate of the forward reaction (r f ) is equal to the rate of the reverse reaction (r r ). Note: The concentrations of both reactants and products are not necessarily equal. The relationship between the concentrations of reactants and products in a reaction at equilibrium is given by the equilibrium expression (K) , also called the law of mass action. K c is a ratio of product and reactant concentrations at a specific temperature. As long as a system is at a constant temperature, the initial concentrations do not affect K c Excludes the following phases: (s)olids and ( )iquids K helps us predict the direction of reaction to reach equilibrium (if we have Q ), and to calculate concentration of reactants and products after equilibrium has been reached.
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Chemistry 1C Page 2 of 8 There is another equilibrium constant for partial pressures, K p , which ONLY applies to gases in a system. It takes the same form as K c . K c and K p are related through the following equations: If the reactants and products have the same number of moles of gas, K c = K p Examples: 14.16 and 14.24 Consider the following equilibrium process at 700 o C: 2H 2(g) + O 2(g) Ù 2H 2 S (g) Analysis shows that there are 2.50 moles of H 2 , 1.35x10 -5 mole of O 2 , and 8.70 moles of H 2 S present in a 12.0-L flask. Calculate the equilibrium constants K c and K p for the reaction. Ammonium carbamate, NH 4 CO 2 NH 2 , decomposes as followings: NH 4 CO 2 NH 2(s) Ù 2NH 3(g) + CO 2(g) Starting with only the solid, it is found that at 40 o C the total gas pressure (NH 3 and CO 2 ) is 0.363 atm. Calculate the equilibrium constants K p and K c .
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Chemistry 1C Page 3 of 8 If a reaction can be expressed as the sum of two or more reactions, its equilibrium constant is given by the product of the individual reactions. I
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Midterm Review-ChemicalEqul - Chemistry 1C Page 1 of 8...

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