topic: equilibrium do now:
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Topic: EQUILIBRIUM Do Now:. VIDEO CLIP. Equilibrium = Balance Not 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 - PowerPoint PPT PresentationTRANSCRIPT
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Topic: EQUILIBRIUMDo Now:
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Equilibrium = BalanceNot necessarily equal
1 man and 1 man equal but not balanced
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BALANCED!
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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
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Time
Conc
entra
tion
NH3
H2
N2
N2(g) + 3H2(g) 2NH3(g)EQUILIBRIUM POINT
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Dynamic Equilibrium
• macroscopic level –looks like nothing is happening
• microscopic level –lots going on
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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!
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• 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
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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
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Reversible Rxn vs Reaction that goes to completionNaOH + HCl --> NaCl + H2O
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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
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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
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Increase Concentration• INCREASING the concentration causes the
equilibrium to shift AWAY from the substance that was added.
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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
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N2 + 3H2 2NH3
• Increase NH3
Need more N2 and H2 so reaction shifts to the left
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• DECREASING the concentration causes the equilibrium to shift TOWARD the substance that was removed.
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N2 + 3H2 2NH3
• Decrease NH3
Need more NH3 so reaction shifts to the right
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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
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!! 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)
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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.
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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)
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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