Topic: EQUILIBRIUM Do Now:
Post on 16-Feb-2016
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Topic: EQUILIBRIUMDo Now:
Equilibrium = BalanceNot necessarily equal
1 man and 1 man equal but not balanced
BALANCED!
Chemical equilibrium• Rate of forward reaction is EQUAL to the
Rate of the reverse reaction• Concentrations are not necessarily equal but
they are constant, unchanging
Time
Conc
entra
tion
NH3
H2
N2
N2(g) + 3H2(g) 2NH3(g)EQUILIBRIUM POINT
Dynamic Equilibrium
• macroscopic level –looks like nothing is happening
• microscopic level –lots going on
Phase Equilibriumphase changes are reversible processes• H2O(l) H2O(g)
• H2O(l) H2O(s)
same substance on both sides, only its phase is different
Liquid – Vapor Equilibrium
NOTE: anytime a gas is involved, the container must be sealed for
equilibrium to be reached- if not the gas will escape!
• Solution Equilibrium– saturated solution with some solid on
the bottom of the container.• As one molecule dissolves, one
molecule precipitates (forms solid).–Ex: Too much sugar in the
coffee.
- EX: CO2 in water
CO2(g) CO2(aq)
favored by high pressure & low temperature
Reversible Reactions• Most chemical reactions are reversible.
• Reactants react to form Products, then the Products react to form Reactants.
• N2(g) + 3H2 (g) 2NH3(g)
• N2 reacts with H2 to form NH3
• at the same time, NH3 is consumed and forms N2 and H2
Reversible Rxn vs Reaction that goes to completionNaOH + HCl --> NaCl + H2O
equilibrium can be changed or affected
• changes in concentration, pressure, temperature affect forward & reverse reactions differently
• composition of equilibrium mixture will shift to accommodate these changes
Le Chatelier’s Principle• When a system at equilibrium is subjected
to a stress, the equilibrium will shift in the direction which tends to relieve the stress.– stress = change in concentration, volume,
pressure, or temperature
Increase Concentration• INCREASING the concentration causes the
equilibrium to shift AWAY from the substance that was added.
N2 + 3H2 2NH3
• Increase N2
At equilibrium
In order to get back to equilibrium, what has to happen?Need more products!
What happens to the amount of H2?Rxn shift to the RIGHT
N2 + 3H2 2NH3
• Increase NH3
Need more N2 and H2 so reaction shifts to the left
• DECREASING the concentration causes the equilibrium to shift TOWARD the substance that was removed.
N2 + 3H2 2NH3
• Decrease NH3
Need more NH3 so reaction shifts to the right
Changes in Temp
• exothermic reaction: A + B C + D + heat– If ↑ temperature, system shifts to consume heat so
shifts to left – so endothermic rxn favored
• endothermic reaction: A + B + heat C + D– If ↑ temperature, system shifts to consume heat so
shifts to right– so exothermic rxn favored
shift in the direction opposite of the “heat” term
!! PRESSURE !!
• Increase PRESSURE, shift toward the side of the equation that has LESS MOLES of GAS.
• Decrease Pressure, shift toward the side of the equation that has MORE MOLES of GAS.
N2(g) + 3H2(g) 2NH3(g)
VOLUME
• Increasing Volume decreases pressure.• Equilibrium will shift toward greater
number of moles of gas.
• Decreasing Volume increases pressure.• Equilibrium will shift toward smaller
number of moles of gas.
Reactions that go to completion – equilibrium can not exist
Formation of a gas which escapesH2CO3 (aq) CO2(g) + H2O (l)
Formation of waterHCl (aq) + NaOH (aq) NaCl (aq) + H2O (l)
Formation of a precipitate (insoluble compound)NaCl (aq) + AgNO3(aq) AgCl (s) + NaNO3 (aq)
A + B C + D
______[B]
______[C]
______[D]
______[A]
[D][C][B][A]Equil. Shift
Stress
right DEC INC INC
left INC INC DEC
right DEC DEC INC
left INC DEC DEC
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