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Chemical Equilibrium

AP Chemistry. Chemical Equilibrium. reactants products. these RATES are equal; NOT amt. of R = amt. of P. Chemical equilibrium is reached when the concentrations of reactants and products cease changing with time. -- system must be closed. --. equilibrium is a dynamic process

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Chemical Equilibrium

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  1. AP Chemistry Chemical Equilibrium

  2. reactantsproducts these RATES are equal; NOT amt. of R = amt. of P Chemical equilibrium is reached when the concentrations of reactants and products cease changing with time. -- system must be closed -- equilibrium is a dynamic process (although it might look static)

  3. either A (i.e., A B) or with B (i.e., A B). Eventually, A B is reached. For the reaction A B: -- Eq. can be reached starting with…

  4. ( ) P i.e., K = R law of mass action: expresses the relationship between amounts of R and P in any reaction this is the “muscle” behind an equilibrium-constant expression -- For the equilibrium system aA + bB pP + qQ the law of mass action says that an equilibrium constant K is given by: When amts. are given in terms of concentration (i.e., molarity):

  5. 0.08206 L-atm/mol-K For a gaseous system: where PX is the partial pressure of X at eq., and Kp is the pressure eq. constant PX values must be in atm. (!) The relationship between Kc and Kp is given by... Kp = Kc(RT)Dn Dn = SPcoeff – SRcoeff R = universal gas const. T = absolute temp.

  6. 2 NO + O2 2 NO2 When a flask filled with colorless NO is opened to the air, O2 enters, resulting in brown NO2. For the gaseous reaction (1) write the Kc and Kp expressions (2) find Kp at T = 750oC, if Kc = 2.19 x 10–3. [NO2]2 Kc = [NO]2 [O2] (1) (PNO2)2 Kp = (PNO)2 (PO2) (2) T = 1023 K = 2.19 x 10–3 [0.08206(1023)]–1 Kp = Kc(RT)Dn = 2.61 x 10–5

  7. A few notes about K: -- it depends only on the reaction stoichiometry, not its mechanism -- it is independent of initial concentrations -- it is unaffected by other substances, as long as they don’t react with R or P -- it varies with temperature -- it is written without units -- it NEVER includes pure liquids or pure solids

  8. CO2(g) + H2(g) CO(g) + H2O(l) SnO2(s) + 2 CO(g) Sn(s) + 2 CO2(g) Write expressions for Kc and Kp. In the refining of iron ore, a common way to reduce Fe2+/Fe3+ from the iron ore is to react FeO/Fe2O3w/CO to form Fe and CO2.

  9. N2 + 3 H2 2 NH3 2 SO3 2 SO2 + O2 Fritz Haber (1868–1934) discovered a way to generate ammonia from hydrogen and nitrogen at high pressure. The ammonia was needed for Germany’s munitions industry, which was cut off from the nitrate sources of South America by the British blockade during WWI. Write the Kc expression for each reaction. ** substances w/only 1 or 2 nonmetals: best guess = gases

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