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| ap_chem:elementary_reactions [2021/01/21 05:50] – created epix | ap_chem:elementary_reactions [2021/01/21 06:30] (current) – Added section on steady state approximation epix |
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| ===== Determining Rate Law ===== | ===== Determining Rate Law ===== |
| The [[ap_chem:rate_of_reaction|rate law]] of an overall reaction can be determined by its elementary steps. The coefficient of a compound in the elementary reaction would be the order of that compound. For the entire equation, put together each compound and its order and cancel out any intermediaries, just like summing for the entire elementary reaction. However, once you reach the Rate Determining Step((it could also be the first, in that case only that elementary step defines the entire reaction's rate)), **disregard the rest** as the rate will be limited by that elementary step as it is the slowest. | The [[ap_chem:rate_of_reaction|rate law]] of an overall reaction can be determined by its elementary steps. The coefficient of a compound in the elementary reaction would be the order of that compound. For the entire equation, put together each compound and its order and cancel out any intermediaries, just like summing for the entire elementary reaction. However, once you reach the Rate Determining Step((this simplified explanation only applies if the rate determining step is **not** first, see the section below if you need that)), **disregard the rest** as the rate will be limited by that elementary step as it is the slowest. |
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| | ==== Steady-State Approximation ==== |
| | If the slowest elementary reaction is not first, you must use steady-state approximation to determine the rate law((this is so we avoid having the intermediary in our final rate law, as it shouldn't be present)). In College Board™ simplified terms, this means equaling two elementary step rate equations, or an equilibrium reaction if present, that share the intermediate and then rearranging for the intermediate. Afterwards, we can plug in the "intermediate" rearranged expression and simplify for our final rate law. Don't be afraid! Disregarding the scientific notation this is pure algebra. |
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| ===== Getting the Rate Determining Step ===== | ===== Getting the Rate Determining Step ===== |
| The rate determining step of an overall reaction is the elementary step with the **slowest rate**. | The rate determining step of an overall reaction is the elementary step with the **slowest rate**. |
