Law of Mass Action dates back to the 1850s and is the progenitor to a lot of this, but in a lot of ways it's an empirical approach to this concept. Looking at reversible reactions they could see that adding reactants drives the forward reaction, but there was no good explanation for this. So it would be misleading to say that this it the law of mass action - law of mass action gives this outcome but doesn't provide a framework beyond empirical experiments. The more rigorous definition of the reaction quotient, Q, is the better explanation, with the requirement that Q = Kc (or Keq, which is the more modern take on K) at equilibrium
@@StubbornAlchemist I am sorry you lost me there; are you trying to approve or disapprove my question? Because I thought this is the stepping stone towards the Law of Mass Action because we know the rates are equal and the ratio of of the rate constants is turn out to be Kc.
I believe you just add all the orders up for both the forward and reverse terms, though it's not been my experience that the overall order is meaningful for reversible reactions and honestly it's not a calculation I've ever done.
@@stevelow7900 I think that is correct, but to be honest I don't think there is a physical meaning for overall order for reversible reactions. for irreversible the order sort of makes sense as it can directly translate into pressure dependence, which is directly observable. but for reversible reaction the observed order will depend on the ratio of products and reactants. sorry to give you such a non-committal answer but I just haven't seen much on this topic.
@@StubbornAlchemist Oooooooo I was quite shocked too haha bcoz I saw this qn in my uni assignment but it wasn't covered in lecture and I can't find anything on internet that talks about the overall order for reversible reaction. Anyways, thank you soooo much for the detailed explanation!!
This is called the Principle of Microscopic Reversibility - if a reaction is elementary in one direction, it must also be elementary in the reverse direction.
If it's not elementary, then you can't derive the rate law directly. you've got a few options instead. The first option is to derive it experimentally, and this will fall into two categories; doing mechanistic studies (in order to determine the reaction mechanism) and the other is to do rate studies. For the first, you would ultimately determine the mechanism and use the mechanism to derive the rate law. For the second, you would just assume a form for the rate law and accept that what you're doing is just a correlation (see my videos on Method of Initial Rates and Graphical analysis). The third option is to run computer simulations of the reaction to determine the most likely reaction mechanism, then determine a rate law, then verify the rate law experimentally.
Awesomely explained 👍🏻
thanks!
Isn't it the "Law of mass action" or Kc equation?! Because I feel like it is!
Law of Mass Action dates back to the 1850s and is the progenitor to a lot of this, but in a lot of ways it's an empirical approach to this concept. Looking at reversible reactions they could see that adding reactants drives the forward reaction, but there was no good explanation for this. So it would be misleading to say that this it the law of mass action - law of mass action gives this outcome but doesn't provide a framework beyond empirical experiments. The more rigorous definition of the reaction quotient, Q, is the better explanation, with the requirement that Q = Kc (or Keq, which is the more modern take on K) at equilibrium
@@StubbornAlchemist I am sorry you lost me there; are you trying to approve or disapprove my question? Because I thought this is the stepping stone towards the Law of Mass Action because we know the rates are equal and the ratio of of the rate constants is turn out to be Kc.
Hi may I know how to find the overall reaction order for reversible reaction?
I believe you just add all the orders up for both the forward and reverse terms, though it's not been my experience that the overall order is meaningful for reversible reactions and honestly it's not a calculation I've ever done.
@@StubbornAlchemist so let say if the forward reaction has order 1 and reverse reaction has order 2, the overall order shld be 1 - 2 = -1?
@@stevelow7900 I think that is correct, but to be honest I don't think there is a physical meaning for overall order for reversible reactions. for irreversible the order sort of makes sense as it can directly translate into pressure dependence, which is directly observable. but for reversible reaction the observed order will depend on the ratio of products and reactants. sorry to give you such a non-committal answer but I just haven't seen much on this topic.
@@StubbornAlchemist Oooooooo I was quite shocked too haha bcoz I saw this qn in my uni assignment but it wasn't covered in lecture and I can't find anything on internet that talks about the overall order for reversible reaction. Anyways, thank you soooo much for the detailed explanation!!
@@stevelow7900 glad I could help
Does all reversible reaction are elementary ?
Because my professor said that "as per kinetics, reversible reactions are elementary "
This is called the Principle of Microscopic Reversibility - if a reaction is elementary in one direction, it must also be elementary in the reverse direction.
What if reaction is not elementaty???
If it's not elementary, then you can't derive the rate law directly. you've got a few options instead. The first option is to derive it experimentally, and this will fall into two categories; doing mechanistic studies (in order to determine the reaction mechanism) and the other is to do rate studies. For the first, you would ultimately determine the mechanism and use the mechanism to derive the rate law. For the second, you would just assume a form for the rate law and accept that what you're doing is just a correlation (see my videos on Method of Initial Rates and Graphical analysis). The third option is to run computer simulations of the reaction to determine the most likely reaction mechanism, then determine a rate law, then verify the rate law experimentally.
@StubbornAlchemist You mean experimentally like calculating the concentrations and the rate, and then ferrer out the rate law?
Thank you
You're welcome