New Unit!:Chemical Equilibrium (Ch.7,8)

Demo:Beaker Water Race!

  • One full/one empty large beaker to start.
  • Each student trying to fill other’s beaker by using small 50 mL beaker to scoop from their own large beaker to other person’s large beaker.

Note:

  • At first, levels in 2 beakers change but then reach an equilibrium point (if 2 students can work at same rate)
  • This is a dynamic system not a static (“nothing happening”) situation, i.e. rxn rate one way equates to rxn rate in opposite direction.
  • At equilibrium, the amounts in each beaker do not need to be the same, just the rate of change of opposing processes.

In dynamic equilibrium:

something is constante.g. temperature, volumes,

concentrations, colour, etc.

something is equal e.g. forward & reverse rxn rate.

Another analogy:

 people at a party  constantly moving between kitchen and family room but if you checked at 8 p.m and 10 p.m. there may be the same number in each room at both times (even though they are not the same individuals you counted before).

Read p.422. Do p.422 #1 – 4

Read p.422 – 428 Define all bold-faced terms.

Do p.428 #1 – 5

Types of Equilibrium

1) Solubility Equilibrium (dissolving process)

e.g. I2(s) I2(aq)

e.g.NaCl(s) Na+(aq) + Cl-(aq)

e.g. CO2 (g) and CO2 (aq) in closed pop bottle

2) Phase Equilibrium (change of state)

e.g. H2O(s) H2O(l)

N.B.: a bit difficult to achieve as ice is also subliming; also, changing air T a big factor.

(ice over lake: at interface of water & thick ice a closer to “perfect” equilibrium could exist)

3) Chemical Reaction Equilibrium (reactants⇆products)

e.g. 2 NH3 (g) ⇆ N2 (g) + 3 H2 (g)

Evidence of dynamic nature of equilibrium

 see Fig.3 p.427

 analogy (tagging people at a party, Disneyland, etc.)

Chemical Reaction Equilibrium

Quantitative Reactions

  • Proceed to completion: reactants  products
  • Occur in an open system: product continually removed

e.g. CaCO3(s)  CaO(s) + CO2(g)

limestonelime

However, if this reaction is performed in a closed vessel, products willaccumulate and eventually force the reverse reaction:

CaCO3(s) CaO(s) + CO2(g)

Note: inside a closed vessel it looks as if the forward rxn has stopped. In reality, the reverse rxn is occurring at the same rate. (equilibrium)

Two Types of Industrial Processes:

“Continuous Processing”:

products continually removed as reactants

used up

“Batch Processing”:

fixed amounts of each reactant placed in

a closed vessel; after rxn completed as far

as it will go,products are then removed

Concentration Time Graph of System Achieving Equilibrium

 see p.430

 Note: Fig. 7 (p.430) and Table 2 (p.431) and

generalization statement above (in blue)

% Reaction at Chemical Equilibrium

 look at Tables 3-5 p.431-433 and description bottom

p.432.

  • Read sample problems p.433-436
  • Hwk. p. 437 Practice #6,7

p.437-438 #1-5, 7-9