Le Chatelier’s Principle Part 1 | Reactions | Chemistry | FuseSchool

Le Chatelier’s Principle Part 1 | Reactions | Chemistry | FuseSchool


In this lesson, you will learn about Le Chatelier’s
Principle, which explains what a system at equilibrium does in response to “stresses”.
Let’s return to our original example of you digging a hole and your friend refilling it
simultaneously. If you start digging at a rate faster than
refilling, the hole gets larger. In order to maintain a constant size of the
hole, your friend must work harder to fill it faster.
Following on the same idea, when a chemical system at equilibrium is stressed, the system
works to restore equilibrium. This is Le Chatelier’s Principle.
The stresses are Changes to the concentration of either the
reactants or products Changes to the pressure, though this is only
applicable to gaseous systems Changes to the temperature
Let’s examine a hypothetical reaction at equilibrium. If we added more A and B, the system becomes
stressed and is no longer at equilibrium. To counteract the stress, the system forms
more C and D, in order to remove the excess A and B.
The equilibrium, therefore, “shifts” to the right.
As you can see, equilibrium has now been restored. If we added more C and D, the system becomes
stressed and is also no longer at equilibrium. To counteract the stress, the system forms
more A and B. Therefore, equilibrium shifts to the left.
What happens if we remove C and D as they are being produced, or in other words, if
the concentration of C and D is decreased? Please pause the lesson to think about this,
and resume when you are done. The system is now stressed and no longer at
equilibrium. To counteract the stress, more C and D are
produced, so equilibrium shifts to the right. When concentration increases, equilibrium
shifts to the opposite side of the reaction. When concentration decreases, equilibrium
shifts to the same side of the reaction. This stress to a system at equilibrium is
only applicable to gaseous systems. For this stress, we will examine another hypothetical
reaction at equilibrium: An increase in pressure means that there is
a decrease in volume, so there is less space. Equilibrium will shift to the side of the
reaction with fewer moles. In our example, an increase in pressure will
cause equilibrium to shift to the right, since there are fewer moles — 2 moles compared
to 3 moles on the left. A decrease in pressure means that there is
an increase in volume, so there is more space. Equilibrium shifts to the side with more moles,
so in our example, equilibrium shifts to the left.
So an increase in pressure favours the side with fewer moles, and a decrease in pressure
favours the side with more moles. In our next lesson, you will learn about how
a system works to restore equilibrium in response to changes in temperature.
In summary, LeChatelier’s principle states that when a system at equilibrium is stressed,
the system works to restore equilibrium.

Comments

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    FuseSchool - Global Education

    will be out very soon – we are currently producing many videos per week – and 300 till September. We ll let you know here once it's out πŸ˜‰

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    Ahmad Badawy

    I can understand how pressure & temperature change & how they effect the reaction & force it back to the opposite direction to maintain equilibrium, but i don't really get it when it comes to concentration change!

    a certain amount of A & B will react to produce a certain amount of C & D, how would the concentration of C & D increase! do we just add more of them ?

    ( Thank you in advance for any help you might be able to provide )

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    Ahmad Badawy

    I also think ( plz correct me if I am wrong ) that reversible reaction ( backward reaction ) due to temperature change is more likely to occur right after the forward reaction is done, without any interference.

    while on the other hand the backward reaction due to ( pressure & concentration ) would require something that causes the pressure change ( I dunno like doing the experiment on a top of a mountain – i know this sounds silly – ) or adding more substance to increase concentration!

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    Ahmad Badawy

    the reason why i have this feeling is that in reversible reactions due to temperature change the reaction produces its own heat in one direction & then uses it to go backwards

    ( Thank you for the awesome video )

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    Amanda Edward

    Hi Ahmad,
    Sorry for the delayed response – basically, adding C and D is a hypothetical situation – a stress that we are putting on to the system, and then seeing how it would respond according to Le Chatelier's principle πŸ™‚
    I hope this helps a bit, please let me know if you want to know more :)))

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    Amanda Edward

    When it comes to changes in temperature, it is depends on whether it is an exothermic (heat-releasing) or endothermic (heat-absorbing) reaction. Please do check out our video on part two πŸ™‚

    In terms of changes in pressure, yes, there is something that causes the change -usually mechanically (such as, a lid being pushed down, so there is less space available) – I hope this helps!

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    Swapnil Nath

    possibly the best explaiantion on le chatalier principle!
    just want to know which idiot disliked this?

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    sugbarnis

    Let's say i have N2 + 3H2 –> 2NH3. I've got 43 mole N2, 152 mole H2 and 335 mole NH3. When I add 15 mole N2 to the system and await equilibrium, what will then happen to the ammount of mole of H2? Will it be more, less or the same?

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    Isis Perez

    OMG THANK YOU SO MUCH! I NEED TO PASS CHEM DURING SUMMER SCHOOL AND I HAVE A SERIOUS TEST TOMORROW AND NOBODY WOULD EXPLAIN(even the teacher) you helped me SOOOO much THANK YOU

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    Pashwa Shah

    I also don't understand why when volume increases equilibrium shifts to the side with more moles. They already are occupying more space as there are more moles. This means they have less volume. So why would equilibrium shift towards them? To further decrease the space?

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    Patricia N'Khani B.

    Life saver! Best explanation of Le Chatelier's principle… thank you, I hope I won't fail my test this Thursday!

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    belikeadbi

    Really GOOD!!! Thanks! It was such a hard thing for me to understand from the book, but this video made it so attractive and arresting that i feel I donot have to look back to my books. Thank you once again. πŸ™‚

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    Mousehead2000

    If A + B are reacting to produce C + D, why there would there be a decrease in C + D in the first place?

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    stargazer JB

    I was having problem in understanding the effect of pressure thing bt dis video explained it impressively…
    Thanxxx

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    vrishaali vyas

    Well initially in school I couldn ' t decipher this concept…but after watching this vid , le chatelier' s feels like a breeze . A big thankyou ! πŸ™‚

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    Melon Genie

    these guys explain concepts in chemistry that i've always found confusing in a way that's so easy to follow, even for my dumb ass πŸ™‚

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    Pradeep Singh

    Still confused about the decrease of products. Surely you can't increase the products without decreasing reactants?

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    syam prasad

    Good.
    For full syllabus of cbse chemistry, may also be referred below for value addition:-
    World of chemistry class 11 and 12.

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    Ali Shamlan

    for 2 years i had been trying to understand the shifting of equilibrium
    my teacher explained it to me over ten times and i watched many videos over 20 and 30 minutes then i come to this 4 minutes video and everything got clear
    cant thank you enough

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    dr.paddlesmack

    not a great explanation of WHY equilibrium shifts to the right and left when pressure is increased and decreased, respectively… You just said according to Le Chatelier's ….

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    Lunna325 De MSP

    For pH indicators, is the stress coming from the pH of the solution? Like the liquid pH indicator is being put into a solution of a certain pH and because of that, the equilibrium is changed and then thats what gives the color to the indicator?

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    Blue Rose

    I don’t get it why when the pressure is increased, the equilibrium shift to the side with fewer moles?

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