Le Chatelier's Principle
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Transcript of Le Chatelier's Principle
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Le Chatelier'sPrinciple
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What if the conditions of the equilibrium changed?
Le Chatelier’s principle states that if a closed system at equilibrium is subjected to a change(stress), things will happen to counteract that change (regain back balance).
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The effect of Temperature changes
Temperature affects heat terms in a reaction.If you increase temperature, you are increasing the heat term(energy). Therefore, the reaction will shift to use up this “extra” heat/energy and go back to original state.
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The Effect of Temperature Changes
A + B ⇌ C + Energy
Change: increase Temp reaction- shifts left
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The Effect of Temperature Changes
A + B + Energy ⇌ C
Change: increase Temp reaction- shifts right
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The Effect of Temperature Changes
A + B + Energy ⇌ C
Change: decrease Temp reaction- shifts left
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The Effect of Concentration Changes
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Adding a reactant or product shifts the reaction in the direction that removes them/uses them up.
A + B ⇌ C + Energy
reaction- shifts rightchange- increase [A]
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Adding a reactant or product shifts in the direction that removes them.
A + B ⇌ C + Energy
stress- increase [C] reaction- shifts left
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Removing a reactant or product shifts reaction to make MORE.
A + B ⇌ C + Energy
change- decrease [A] reaction- shifts left
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Removing a reactant or product shifts reaction to make more.
A + B ⇌ C + Energy
change- decrease [C] reaction- shifts right
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Effect of pressure changes
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A(g)
+ B(g)
⇄
AB(g)
2 mols 1 mol
more pressure less pressure
Usually we refer only to gases(g) when we talk about pressure changes.
Those pressure changes we control by changing the volume.
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As you know…• If you decrease the volume, you increase the pressure.
• If you increase the volume, you decrease the pressure.
• Also, increasing pressure increases the concentrations of ALL gaseous species found.
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Where to start?
• First identify where there is more pressure or where there is less pressure by counting up the molecules of gas you have on each side.
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4HCl(g)
+ 2O2(g)
⇄ 2H2
O(l)
+ 2Cl2(g)
If we decreased the volume, pressure will ________ and so the reaction will go to low pressure side.
less pressure
6 mols 2 mols
more pressure
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2SO3(g)
⇄ 2SO2(g)
+ O2(g)
more pressureless pressure
2 gas 3 gas
If we increased the volume, pressure will _________, so the reaction responds by…
increasing pressure again and goes to more pressure side
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We decrease the volume, we increase pressure!
Increasing the pressure by decreasing the volume shifts to the eqlm fewest gas molecules. Only (g) count for gas particles.
4HCl (g)
+ 2O2 (g)
⇄
2H2
O (l)
+ 2Cl2
(g)
+ 98kJ
The reaction responds by shifting to right to decrease the pressure!
6 2
All concentrations go up!
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5A(g) + 2B(g) 4C⇌ (g) + 5D(g)
We ⇑ P
The Reaction opposes and goes to low pressure side⇓ P
7 9
We ⇓ V
Shifts left
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4A(g) + 2B(g) 3C⇌ (g) + 2D(g)
6 5
We ⇓ V
We ⇑ P
What volume change shifts right?
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2A(g) + 2B(g) 3C⇌ (g) + 4D(g)
We ⇓ P
4 7
We ⇑ V
What volume change shifts right?
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4HCl (g)
+ 2O2 (g)
⇄
2H2
O (l)
+ 2Cl2
(g)
+ 98kJ
Describe the shift in the above equilibrium system for each stress indicated.
Stress Shift [HCl] [O2
] [Cl2
]
↓←↑ V
↑↑ ↑ ←↑ [Cl2
]
――――Add water
↓↓↑←
↑↑ ↓→↑ [HCl]
↓ [O2
]
↓ ↓
When the volume increases, pressure decreases and all concentration go down
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reactants
Adding a catalyst does not shift the equilibrium
Equilibrium is attained faster
Forward and reverse rates are increased by the same amount
products
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Adding an inert (non-reactive) gas does not shift the equilibrium.
Adding Ne(g)
2NH3(g) ⇌ N2(g) + 3H2(g)
No shift!
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Homework
Need this to be done by next classExercises 17-23 on page 54.
Exercises 24-26, do NOT graph, only state what each change/stress would do to the equilibrium (ie; where it shifts it)
Have a fan-ta-bulous weekend!