a. Adding more reactant/products
b. Changing Temperature (really means increase Energy).
c. Pressure change (there are more than one way to do this)
d. Add a catalysts
FYI, only substances or attributes that are found in the reversible reaction can stress the equilibrium system (shift the equilibrium).
Here is a link to a Flash Animation on LeChatelier's Principle,[LeChatlier's Principle Flash Animation]
I will use the following chemical reaction (called the Habor process, 1st process to fix nitrogen to ammonia industrially) for examples of LeChatelier's Principle
1 N2 (g) + 3 H2 (g) <==> 2 NH3 (g) + Energy (i.e. exothermic rxn)
I will use the above blank answer form but will also include explanations of why. When you do your homework , you do not have to include explanations (I will italicize the words) and you will circle some answer that I bolded below (can't circle with computer).
Circle: Make more product or more reactant (fill in for pressure changes)__________________
Comment: since I am consuming product, I am making more reactant
Circle: Favoring: Forward rxn or Backward rxn: (fill in for temperature changes) _____________
Comment: Favoring reaction means that overall that reaction is used more than the other reaction. Remember since this is equilibrium, both the forward and backward reaction occurs, but in this case overall the backward reaction was done more than the forward reaction
Circle: Shift Equilibrium to: Left(more reactant) or Right (more product)
Comment: Since the new equilibrium position has more reactant than the original equilibrium position, we say the equilibrium is shifted to the Left (side pointing to the reactant).
Circle: Make more product or more reactant (fill in for pressure changes)__________________
Comment: Since reaction wants to make Energy, Energy should be a "product" so it is the product in the forward reaction which we call the product.
Circle: Favoring: Forward rxn or Backward rxn: (fill in for temperature changes): Forward reaction is the Exothermic reaction
<i>Comment: Since we want to make Energy, the forward reaction (which is Exothermic) will occur (overall) more than the reverse reaction.
Circle: Shift Equilibrium to: Left(more reactant) or Right (more product)
Comment: Since we want to make more Energy in the new equilibrium position than the original equilibrium position, the other products will be in greater amount also.
Comment: In this concept, you can equate pressure of gas (does not work for liquid or solids since they are incompressible) to number of particles per volume. So if you decrease pressure, you are reducing the number of particles per volume (i.e. removing particles).
Reason to Pressure = Number of particles: As you know, only attributes or substance in the reversible reaction shift equilibrium and there is no pressure term in the reaction. However, there are number of particles of each species of reactant and product in the form of coefficients.
Stress: Decreasing Pressure (Decreasing/removing/consuming number of particle
How rxn tries to remove stress: Increase Pressure (Increase/make particle
Circle: Make more product or more reactant (fill in for pressure changes): 2 product particles --> 4 reactant particles
Comment: Remember that the system can only 2 things to get rid of the stress, run the forward reaction or run the backward reaction. (Of course, you know that both reaction will occur before you reach equilibrium but "run" means overall which reaction occurs more). In this reaction, there are 4 reactant particles and 2 product particle (you only consider substances in gas phase). So the forward reaction decreases number of particle since 4 reactant particles become 2 product particles and the backward reaction increases number of particles since 2 product particles become 4 reactant particles. In this case, the system wants to increase particles so you write, "2 product particles --> 4 reactant particles" thereby making more reactants.
Circle: Favoring: Forward rxn or Backward rxn: (fill in for temperature changes) _____________
Circle: Shift Equilibrium to: Left(more reactant) or Right (more product)
Note: What would happen to the above if the number of reactant particles and number of product particles are the same.
Answer: No affect on equilibrium.
So you fill out stress portion and then explain in How rxn tries to remove stress portion that #
d. Add a catalysts
<i>Comment: Two major attributes of a Catalysts are: 1) Changes the rate of reaction (how fast products can be made (by changing the activation energy (Eac) via changing reaction mechanism) and 2) Does not get consumed in overall chemical reaction.
A Major attributes of Equilibrium is that it does not care about time ( it is time independent). So Catalysts DO NOT SHIFT THE EQUILIBRIUM.
Stress: Adding a catalyst
Comment: For Habor process, there have been several and most are iron containing compound
How rxn tries to remove stress:Catalysts do not affect Equilibrium
Circle: Make more product or more reactant (fill in for pressure changes): N/A
Circle: Favoring: Forward rxn or Backward rxn: (fill in for temperature changes): N/A
Circle: Shift Equilibrium to: Left(more reactant) or Right (more product): N/A
Comment: So after stating in the "How rxn tries to remove stress" line that catalysts do not affect equilibrium, the rest of the "answers" you fill in as N/A (even the one you are circling).