1. Chemical Equilibrium AP Chemistry

2. 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)

3. 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.

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

5. For a gaseous system: where P X is the partial pressure of X at eq., and K p is the pressure eq. constant The relationship between K c and K p is given by... K p = K c (RT)  n  n =  P coeff –  R coeff R = universal gas const. 0.08206 L-atm/mol-K T = absolute temp. P X values must be in atm. (!)

6. For the gaseous reaction 2 NO + O 2 2 NO 2 (1) write the K c and K p expressions (2) find K p at T = 750 o C, if K c = 2.19 x 10 –3. (2) T = 1023 K K p = K c (RT)  n = 2.19 x 10 –3 [0.08206(1023)] –1 = 2.61 x 10 –5 When a flask filled with colorless NO is opened to the air, O 2 enters, resulting in brown NO 2. (1) K c = [NO 2 ] 2 [NO] 2 [O 2 ] K p = (P NO2 ) 2 (P NO ) 2 (P O2 )

7. -- 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 A few notes about K: -- it NEVER includes pure liquids or pure solids

8. Write expressions for K c and K p. CO 2 (g) + H 2 (g) CO(g) + H 2 O(l) SnO 2 (s) + 2 CO(g) Sn(s) + 2 CO 2 (g) In the refining of iron ore, a common way to reduce Fe 2+ /Fe 3+ from the iron ore is to react FeO/Fe 2 O 3 w /CO to form Fe and CO 2.

9. Write the K c expression for each reaction. N 2 + 3 H 2 2 NH 3 2 SO 3 2 SO 2 + O 2 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. substances w /only 1 or 2 nonmetals: best guess = gases **