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CHEMICAL CHEMICAL EQUILIBRIUMEQUILIBRIUM

Chapter 16Chapter 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

H2 + I2 ↔ 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

H2 + I2 ↔ 2HI

2HI ↔ H2 + I2

reactants products

Left Right

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

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Reversible ReactionsReversible 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

H2 + I2 ↔ 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-

CuCl4 (aq) ↔ Cu+ (aq) + Cl- (aq) + heatLeft: GREEN Right 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 fun29778 bleaching

Concentration:Amount

ADD reactant or

REMOVE reactant

Will cause opposite results

Science is fun31918

Cu and hydrogen

PressureUsed for gases Easiest way to measure the amount of a gas

Same affect as changing the concentration

17Equilibrium 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 blueCo(H2O)6Cl2 ---> Co(H2O)4Cl2 + 2 H2 H22OO

Blue to pinkCo(H2O)4Cl2 + 2 H2O ---> Co(H2O)6Cl2

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.Temperature2. Concentration

3. Pressure.