Chapter 13. Chemical Equilibrium

Transcription

1 hater 1. heica Equiibriu

2 Equiibriu Equiibriu: The condition of a syste in which coeting infuences are baanced. (hysica Science Therodynaic equiibriu, when interna rocesses of a syste cause no overa change in teerature or ressure Dynaic equiibriu, when two reversibe rocesses (in therodynaics occur at the sae rate heica equiibriu, when a cheica reaction roceeds at the sae rate as its reverse reaction, with no change in the aount of each coound Mechanica equiibriu, when the su of the forces and oents on each artice of a syste is zero Quasistatic equiibriu, when interna rocesses change graduay fro one equiibriu state to the next (Matheatics n equiibriu oint of a dynaica syste. (ioogica Science unctuated equiibriu, a art of evoutionary theory that states that seciation occurs reativey quicy with ong eriods of itte change in between. (Econoics Econoic equiibriu, a baance of suy and deand Static equiibriu (econoics, an intersection of suy and deand Genera equiibriu, a coex theory of icroeconoics atterson equiibriu, a theory of efficiency and syste disrution (Gae theory Nash equiibriu, an otia coective strategy in a gae invoving two or ore ayers (Ethics Refective equiibriu, a state of baance aong a set of beiefs (fro Wiiedia

3 heica Equiibriu NO + NO (g N O 4 (g in a cosed vesse heica equiibriu: The state where the concentrations of a reactants and roducts reain constant with tie. On the oecuar eve, there is frantic activity. Equiibriu is not static, but is a highy dynaic situation. NO + NO (g N O 4 (g

4 Equiibriu ondition O(g+ O(g (g+o (g Why equiibriu?

5 Equiibriu ondition haracteristics of heica Equiibriu N (g+ (g N (g t 5 o, no concetration changes. ossibiities 1. The syste is at cheica equiibriu.. The forward and reverse reactions are so sow that the syste oves toward equiibriu at a rate that can not be detected. t high T and To reach cheica equiibriu, the reaction rate shoud be big enough to be detected.

6 Equiibriu onstant Law of ass action : ato Maxiiian Gudberg, eter Waage's ostuation ( D t equibriu, Equiibriu exression is D : concentration at equibriu : Equiibriu constant (no unit Ex at eq, N =.1x1 - M N = 8.5x1-1 M =.1x1 - M a.? N (g+ (g N (g (17 o N.81 N N 1 '.61 N 4 5 b. ' for c. " for N (g N (g + (g? 1/ N (g+ / (g N (g? " N 1/ N 1/ 1.91 / N N 1/

7 Equiibriu onstant N (g+ (g N (g o N 4 o.8 1 (5 6.1 N N ( 17 N (5 o Equiibriu osition Equiibriu constant is the sae regardess of the initia concetration at a given teerature.

8 Equiibriu Exressions Invoving ressures (g + (g (g + D(g n D n D D V n n V n n D Ex NO(g + (g NO(g 5 o at eq, NO = 1. at NO = 5.x1 - at =.x1-1 at?? 4 1 ( (98 (.86 1 ( (. 1 (5. 1. n NO NO

9 eterogeneous Equiibria eterogeneous equiibria: equiibria that invove ore than one hase. ao (s ao(s + O (g ' 1 O O ao ao O The osition of a heterogeneous equiibriu does not deend on the aounts of ure soids or iquids resent. O( (g + O (g O(g (g + O (g ( ( O O ( ( ( O O O O

10 ications of the Equiibriu onstant Equiibriu constant to redict tendency of the reaction to occur (not the seed of the reaction Extent of a Reaction + + D D >> 1 : at eq, osty roducts resent << 1: at eq, osty reactants resent owever, the size of and the tie required to reach equiibriu are not directy reated. deends on E. Reaction rate deends on E a. therodynaicay stabe

11 ications of the Equiibriu onstant Reaction Quotient + + D : initia concentration Q = : at equiibriu, no shift Q > : to reach equiibriu, reactants roducts Q < : to reach equiibriu, reactants roducts D Q D : concentration at eq

12 ications of the Equiibriu onstant acuating Equiibriu ressures and oncentrations Ex N O 4 (g NO (g =.1, NO4 =.71 at Equiibriu of NO? ( NO N O 4 NO N O

13 ications of the Equiibriu onstant acuating Equiibriu ressures and oncentrations Ex 5 (g (g + (g 1. L fas n( =.98 o =.98 o/1.l =.98 M n( = o = M n( 5 = 8.7 x 1 - o 5 = 8.7 x 1 - M at eq, at eq, n( =. x 1 - o =. x 1 - M? 5 (g (g + (g. o. o +.o 5 = 8.7 x 1 - M -. x 1 - M = 6.7 x 1 - M =.98 M +. x 1 - M =. M ( -.1 (

14 ications of the Equiibriu onstant acuating Equiibriu ressures and oncentrations Ex O(g + O(g O (g + (g t T = 7, = L fas n(o = 1. o n( O = 1. o n(o = 1. o n( = 1. o Q = 1, = 5.1. equibriu O(g + O(g O (g + (g eq concentrations of a secies? initia 1. M 1. M 1. M 1. M eq (1.-xM (1.-xM (1.+xM (1.+xM (1. x(1. x (1. x(1. x (1. (1. x x x.87m O = O =.61 M, O = = 1.87 M

15 ications of the Equiibriu onstant acuating Equiibriu ressures and oncentrations Ex (g + F (g F(g t a T, =1.15x1. 1.5L fas n( =. o n(f =. o n(f =. o F F Q F F 1..o 1.5L equiibriu.m eq concentrations of a secies? (g + F (g F(g initia. M. M. M eq (.-xm (.-xm (.+xm (. x (. x(. x (. x 115 (. x x 1.5M = F =.47 M, F = 5.6 M

16 Soving Equiibriu robes 1. aance the equation.. Write the equiibriu exression.. List the initia concentrations. 4. acuate Q and deterine the shift to equiibriu. 5. Define equiibriu concentrations. 6. Substitute equiibriu concentrations into equiibriu exression and sove. 7. hec cacuated concentrations by cacuating. Ex (g + F (g F(g t a T, =1.15x1..L fas n( =. o, n(f = 6. o, n(f = o, eq concentrations of a secies? (g + F (g F(g F F 115.o 1.M.L 6.o F.M.L F M F Q 1.15 F 1 equiibriu (g + F (g F(g initia 1. M. M M eq (1.-xM (.-xm (xm (x (1. x(. x x.14m or.1.968m, M, 115 F 1.M, 111x x.968m 45x ( x 1.M F 1.96M F F 11

17 Soving Equiibriu robes Ex (g + I (g I(g t a T, =1.x1..L fas ( = 1.x1 - at, (I = 5.x1 - at, (I = 5.x1-1 at, eq ressure of a secies? (g + I (g I(g ( I Q I I I ( n at at at equiibriu ( I I (g + I (g I(g initia 1. x 1 - at 5. x 1 - at 5. x 1-1 at eq (1. x x (5. x 1 - +x (5. x 1-1 -x x.551 I I 1 (5. 1 x (1. 1 x( at 1 at at at x n( V 1.1 I I 99.9

18 Soving Equiibriu robes Treating Systes That ave Sa Equiibriu onstants Ex NO(g NO(g + (g t T=5 o, =1.6x1-5..L fas n(no = 1. o, eq concentrations of a secies? NO Q 1.o.5M.L equiibriu NO(g NO(g + (g initia.5 M M M eq (.5-xM (xm (xm 1.61 x 1.1 (x ( x (.5 M NO.5 x.5m NO x.1 x M M x ( x (.5 x ( very sa x is exected..5 - x.5 chec 6 (.1 (1. 1 ( M

19 Le hâteier's rincie N (g+ (g N (g in aber-osch rocess aber tried to axiize the roduct. Le hâteier's rincie: if a change is iosed on a syste at equiibriu, the osition of the equiibriu wi shift in a direction that tends to reduce that change. be aware of : therodynaicay ow te is better, but have to consider inetic effect.

20 Effect of a hange in oncentration Le hâteier's rincie N (g + (g N (g eq.99 M M. ( (.99(1.197 add 1. M Q ( (1.99(1.197 equiibriu eq (1.99-xM (1.197-xM (.+xm. x (1.99 x(1.197 x ( x.51m eq 1.48M 1.44M.4M oncentration: The syste wi shift away fro the added coonent

21 Le hâteier's rincie Effect of a hange in ressure (for gases (g + (g (g + D(g D 1. ddition or reoving of a gasesous reactant or roduct: sae thing as concentration change. ddition of an inert gase (one not invoed in the reaction: no effect on the equiibriu osition. 1at, 1at, at, at, at, adding 5at of e at, 4at, D D 4at e tota 5at 1at tota 15at. hanging the voue of the container: Decreasing the voue shifts the equiibriu toward the side with fewer oes. Increasing the voue shifts the equiibriu toward the side with ore oes. If, Q V V, ( ( (D ( n ositive, equiibriu. If n negative, equiibriu., n D D NO (g N O 4 (g brown cooress

22 Effect of a hange in Teerature Le hâteier's rincie Equiibriu constant: function of teerature (not ressure, not concentration N (g+ (g N (g + 9 J T, equiibriu (to reduce the change,. hanging the voue of the container: Decreasing the voue shifts the equiibriu toward the side with fewer oes. Increasing the voue shifts the equiibriu toward the side with ore oes., equiibriu, constant

23 Le hâteier's rincie Ex Shifts in the equiibriu osition for the reaction NO (g N O 4 (g + 58J cooress brown None