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chem: equilibrium

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In which direction does the equilibrium shift for the following reaction?

SO2(g) + NO2 (g) <-> SO3(g0 + NO(g) + 42 KJ


a. temperature increases
b. pressure increases
c. [SO2] increases
d. [NO2] increases
e. temperature decreases
f. [No] increases


Im confused on knowing which way it would shift. thanks!

  • chem: equilibrium -

    Le Chatelier's Principle sounds so great when we spit that out in the classroom. When done really right it sounds so esoteric; so learned. Unfortunately, many students don't understand what is going on. So here is a very common way of saying it. It doesn't sound as nice BUT it tells you how to answer these things. Here it is in a nutshell. When we do something to a system in equilibrium it will undo what we've done. Simple, huh? Here's how it works with the first one.
    The system is exothermic. It gives off heat when it reacts. So if we increase the temperature it will try to undo that. How can it do decrease the temperature? By shifting to the left BECAUSE when it moves to the left it users up some of the heat we added.
    Next, SO2 is increased. So we add SO2 and it tries to decrease SO2. How can it do that? By shifting to the right, it uses up some of the SO2 we've added. That means, of courser, that SO3 is increased, NO is increased, and heat is increased. It also means NO2 is decreased because it uses NO2 when the forward reaction occurs.
    Last one. Pressure is increased. You can go through this the same way but the easy way is a modification that I see used all the time. Pressure increase shifts the equilibrium to the side with the fewer mols OF GAS. In this case there are two mols gas on the left and two mols gas on the right; therefore a change in pressure (up or down) will not change the equilibrium. I'll leave the others for you.

  • chem: equilibrium -

    Thanks, your explanation was a great help!

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