AP Chemistry Chemical Equilibrium Chemical equilibrium is reached

AP Chemistry Chemical Equilibrium

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

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

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 a. A + b. B the law of mass action says that an equilibrium constant K is given by: ( p. P + q. Q P i. e. , K = R When amts. are given in terms of concentration (i. e. , molarity): )

For a gaseous system: where PX is the partial pressure of X at PX values must eq. , and Kp is the pressure eq. constant be in atm. (!) The relationship between Kc and Kp is given by. . . Kp = Kc(RT)Dn Dn = SPcoeff – SRcoeff R = universal gas const. 0. 08206 L-atm/mol-K T = absolute temp.

For the gaseous reaction 2 NO + O 2 2 NO 2 (1) write the Kc and Kp expressions (2) find Kp at T = 750 o. C, if Kc = 2. 19 x 10– 3. [NO 2]2 (1) Kc = [NO]2 [O 2] (2) Kp = When a flask filled with colorless NO is opened to the air, O 2 enters, resulting in brown NO 2. (PNO 2)2 (PNO)2 (PO 2) T = 1023 K Kp = Kc(RT)Dn = 2. 19 x 10– 3 [0. 08206(1023)]– 1 = 2. 61 x 10– 5

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

Write expressions for Kc and Kp. CO 2(g) + H 2(g) Sn. O 2(s) + 2 CO(g) + H 2 O(l) Sn(s) + 2 CO 2(g) In the refining of iron ore, a common way to r Fe 2+/Fe 3+ from the iron ore is to react Fe. O/Fe 2 to form Fe and CO 2.

Write the Kc expression for each reaction. ** substances w/only 1 or 2 nonmetals: best guess = gases N 2 + 3 H 2 2 SO 3 2 NH 3 2 SO 2 + Fritz Haber (1868– 1934) discovered to generate ammonia from O 2 a way 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.