Chemical Equilibrium. A. Di Lallo

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Phyllis Taylor
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1 Chemical Equilibrium

2 Reversible vs Irreversible Rxn Irreversible rxn one direction only React prod Examples: combustion rxn, decomposition of food Reversible rxn both directions React prod and Prod react When rates of the two opposing reactions are equal, you get chemical equilibrium!

3 Irreversible reaction Reversible reaction

4 Static Static vs Dynamic Equilibrium Completely immobile, system remains at a given point Dynamic Two opposing processes occurring at same rate so that no visible change takes place Involves reversible reactions Three types Phase Solubility **Chemical** (what we re really concentrating on)

5 Dynamic Equilibrium Phase: single substance found in several phases as a result of physical changes Sealed bottled water Solubility: solute is dissolved in a solvent and an excess of solute is in contact with the saturated solution Sugar in coffee

6 Chemical Equilibrium Def: Dynamic Equilibrium which is a result from two opposing chemical reactions that occur at the same rate, leaving composition of the reaction system unchanged Rxn must be reversible Equilibrium must be the result of chemical change between a reactant and a product r r for rev You are in a state of dynamic equilibrium when the forward rxn rate is equal to the reverse rxn rate

7 Chemical Equilibrium

8 Conditions for Attaining Equilibrium Must have a reversible reaction Change must occur in a closed system **Macroscopic properties are constant** Macroscopic = visible to naked eye Colour, volume, ph, temperature, pressure It by itself it is not proof

10 Le Chatelier s Principle If the conditions of a system in a state of equilibrium change, the system will react to partially oppose this change until it attains a new state of equilibrium

12 Le Chatelier s Principle Factors that affect state of chemical equilibrium Concentration Temperature Pressure The story of Mr. Catalyst

13 Key about Le Chatelier Whatever side you place the stress on, the reaction will shift in the opposite direction to relieve that stress and get back to equilibrium

14 Systems in disequilibrium eutrophication Eutrophication Fertilization of surface water by previous scare nutrients nutrients phytoplankton, benthic and epiplagic algae and bacterial biomass anoxia in deep water mortality of fish and shellfish in water transparency

18 Equilibrium Constant Relationship between [prod.] and [react], (at a given temp) each raised to the power of their stochiometric coefficients

19 Now, equilibrium is defined as r r for rev

20 Equilibrium Constant Given the equation Kc : [C], [D] [A], [B] a,b,c,d K c aa bb cc [ C] [ A] c a [ D] [ B] Equilibrium Constant Conc. of prods (mol/l) Conc. of react (mol/l) Stoich. Coeff of balanced equation b dd Just like in rate law, only consider gases or substances in solution

21 Equilibrium Constant Just like you can get Kc for the forward rxn, can get it for the reverse K c rev K 1 c for

22 Effect of Temperature on K Only temperature can change K; conc. P and V will not alter K Why temp must specified when providing K What s happening? Le Chatelier! When shifting equili, react or prods are being made as a result of temperature New equili won t have conc. proportions that are the same from initial equili

23 How to calculate K R.I.C.E/I.C.E

24 How to calculate K R.I.C.E/I.C.E Stands for Reaction (if you Google it, some have the R, some don t) Initial Change Equilibrium

Acids and Bases:2 key theories Arrhenius theory of acids and bases Acid: sub. when dissociates in water produces H+ Base: sub. when dissociates in water produce OH- Limitations to this theory!

25 Acids and Bases:2 key theories Arrhenius theory of acids and bases Acid: sub. when dissociates in water produces H+ Base: sub. when dissociates in water produce OH- Limitations to this theory! H+ wouldn t exist in water, would form H3O+ Can t explain why solutions with NH3 are basic Cant s explain why some salt solutions without H or O present basic properties Brønsted-Lowry theory of acids and bases Acid: sub. which a proton can be removed Proton donor Base: sub. that can remove proton from acid Proton acceptor

26 Conjugate acid Conjugate base Conjugate acid-base pair Conjugate acid-base pair

28 ph and poh ph: Measure of the acidity of solution Concentration of H3O+ ions per mol/l in a solution ph [ H O 3 log[ H O ] 10 3 ph ] poh: Measure of the bascisty of solution Concentration of OH- ions per mol/l in a solution poh log[ OH ] [ OH ] 10 poh

29 Ionization constant of water ph of water is 7.why? [ H O 3 ] [ OH ] 1.0x10 7 mol / L 2H O 2 ( l ) H O 3 ( aq) OH ( aq) K w [ H O 3 ][ OH ] Kw : [H3O+] [OH-] Ionization constant of water Conc. of hydronioum ion (mol/l) Conc. of hydroxide ion (mol/l

30 Kw always equals 1.0 x 25 C [ H O 3 ] [ OH ] 1.0x10 7 mol / L K K w w [1.0 x10 1.0x ][1.0 x10 7 ] Using this logic, at any given moment, knowing either the ph or poh, you can calculate the number of hydronium or hydroxide ions

31 Acidity and Basicity Constants Indicates the strength of the acid or base at equilibrium Weaker acid/base smaller value of acidity/basicity constants HA K a ( aq) H2O( l) H3O( aq) A( aq) Ka /Kb : [H3O+]/ [OH-] : [HA]/[B]: [A-]/[HB+]: [ 3 H O ][ A [ HA] ] B ( aq) H2O( l) HB( aq) OH( aq) K b [ HB ][ OH [ B] Acidity/Basicity constant Conc. of hydronioum/ hydroxide ion (mol/l) Conc. of un-dissociated acid/base (mol/l) Conc. of conjugate base/acid (mol/l) ]

32 Solubility Product Constant Similar stories to Ionization Constant But talking about salts dissolving now! X n Y m( s) nx ( aq) my ( aq) K sp [ X ] n [ Y ] m Ksp: Solubility product constant [X+], [Y-] : Conc. of ions (mol/l) n, m: Coeff of each ions in balanced equ

Revision Notes on Chemical and Ionic Equilibrium

Revision Notes on Chemical and Ionic Equilibrium Equilibrium Equilibrium is the state of a process in which the properties like temperature, pressure, and concentration etc of the system do not show any