1 CHEMICAL EQUILIBRIUM Chapter 16

OBJECTIVE Distinguish between reversible and completion reactions Understand Equilibrium Define/ apply the terms system and stress to reversible reactions Le Chatlier’s Principle

Reversible Reactions H 2 + I 2 ↔ 2HI the products may react back to original reactants. “closed system”: ONLY if all reactant are present If one piece is completely gone it has ”gone to competition” and no longer reversible

TWO REACTIONS only difference is the Direction H 2 + I 2 ↔ 2HI 2HI ↔ H 2 + I 2 reactants products LeftRight

Examples: Reversible Reactions. Unopened Soda Breathing Rechargeable batteries Color changing shirt

Equilibrium The state in which a chemical reaction and its reverse reaction occur at the same rate.

Equilibrium = No change in amount over time

8 Reversible Reactions Product conc. increases and then becomes constant at equilibrium Reactant conc. declines and then becomes constant at equilibrium Equilibrium achieved

“System” Any reversible reaction H 2 + I 2 ↔ 2HI noted by the double arrow; ↔

“stressing a system” Pick reversible reactions that have different colored products. EXAMPLES T –shirt ball Stress: done to change the ratio color change means change ratio of two products

Le Chatelier’s Principle If a system at equilibrium is stressed, it will react to undo the stress.

Le Chatelier’s Principle Anything YOU do (stress) to a reversible reaction, the system reacts in a way to UNDO that change Remember there are TWO reactions going in every reversible reaction.

Shifting Equilibrium Change Temperature Change concentration of Cl- CuCl 4 (aq) ↔ Cu + (aq) + Cl - (aq) + heat Left: GREENRight BLUE Add Temperature or Cl- : Green/ right Remove heat or Cl: Blue / Left

Temperature ADD energy or REMOVE energy Will cause opposite results Science is fun bleaching

Concentration: Amount ADD reactant or REMOVE reactant Will cause opposite results Science is fun Cu and hydrogen

Pressure Used for gases Easiest way to measure the amount of a gas Same affect as changing the concentration

17 Equilibrium Disk 6C32 Equilibrium systems are DYNAMIC (in constant motion) REVERSIBLE can be approached from either direction Equilibrium systems are DYNAMIC (in constant motion) REVERSIBLE can be approached from either direction Pink to blue 2 H 2 O Co(H 2 O) 6 Cl 2 ---> Co(H 2 O) 4 Cl H 2 O Blue to pink Co(H 2 O) 4 Cl H 2 O ---> Co(H 2 O) 6 Cl 2

Le Chatelier’s Principle If you ADD reactants, The system will REMOVE reactants by making more products. If you REMOVE reactants, The system will ADD reactants by USING (reacting) products.

LEFT:RIGHT: ↔

STRESS to SYSTEM Three stress’s are 1.Temperature 2. Concentration 3. Pressure.