Class Blog 3/31/14

WELCOME BACK!!

TODAY’S NOTES 3/31/14

Le Chatelier’s Principle

Systems at equilibrium

-once something is at equilibrium you can nudge it to get it out of equilibrium

Does not like that

Textbook definition: --When a change/stress (in concentration, temperature, pressure, volume, addition of catalyst…) is applied to a system that is already at equilibrium, the position of equilibrium SHIFTS in a direction that tends to reduce the effect of that change

i.e.: -If a system is at equilibrium and you add reactants, it will shift to make more products until it reaches equilibrium again

i.e.: -If you add more heat, it will shift back to the place when it has less heat

3 Delta’s to think about:

1. Concentration

2. Pressure and volume

3. Temperature

1. Delta (change) in concentration

• When a reactant/product is added to a system that is at equilibrium, the system shifts away from the added component
• If a reactant or product is removed, the system shifts towards the removed component
• i.e. A(aq) + B(aq) → C(aq) + D(aq)
• add more A and the system shifts right to remove extra A

*Aqueous and gas rule applies

2. Delta (change) in pressure/volume

• Gas Laws:
• As volume goes down, pressure goes up (keeping temp constant)
• As volume goes up, pressure goes down (keeping temp constant)
• Systems that involve gases
• i.e.: 2A(g) + B(g) → 3C(g) + D(g)
• (3 moles reactants & 4 moles products)
• pressure increases, system shifts to the side with fewer molecules/moles of gas
• pressure decreases, system shifts to the side with more molecules

*Change of volume is “code” for change in pressure

3. Delta (change) in temperature

• Reminder: The value of k does change with temperature!
• Exothermic reaction: A(g) + B(g) → 3D(g) + heat
• As temp goes up, reaction shifts left (to try to get rid of extra heat energy)
• Endothermic: heat + A(g) + B(g) → 3D(g)
• As temp goes down, reaction shifts right

*Shifts away from thing that is making stress

Look at 4 HANDOUTS

-Intro to LeChatelier’s Principle

-LeChatelier’s Principle 1

-LeChatelier’s Principle 1 (cont)

-LeChatelier’s Principle 2

FINISHED 1st 2 worksheets in class (completed copies in notes folder)

HOMEWORK:

-Webassign due tomorrow at 11:59 pm

Finish worksheets:

-LeChatelier’s Principle 1 (cont)

-LeChatelier’s Principle 2

The next scribe: KATE MAKI