From 0925b6222dd0ae05c7dac44e0daeaea388513db6 Mon Sep 17 00:00:00 2001 From: eggy Date: Sun, 5 Dec 2021 12:04:58 -0500 Subject: [PATCH] chem: Add Le Chatelier's principle --- docs/sch4uz.md | 37 +++++++++++++++++++++++++++++++++++++ 1 file changed, 37 insertions(+) diff --git a/docs/sch4uz.md b/docs/sch4uz.md index e4f0260..58c1a4d 100644 --- a/docs/sch4uz.md +++ b/docs/sch4uz.md @@ -495,6 +495,43 @@ It consists of: | Change | $-y$ | $-y$ | $+2y$ | | Equilibrium | 0.11 | 0.50$-y$ | $+2y$ | +### Le Chatelier's principle + +Le Chatelier's principle states that: If there is a change in a system at equilibrium, the position of equilibrium will readjust to minimise the effect of the change. + +The changes that this principle affects — and therefore affect equilibrium — include changes in temperature, concentration, and pressure. These changes are assumed to occur instantaneously, which may result in sudden theoretical spikes in concentration-time graphs. + +The initial rate of the change will start **fast** and then slow down, appearing as a sharp change instead into a curve in a concentration-time/reaction progress graph that **never return to its original value**. + +!!! tip + Drawing horizontal dotted lines that represent the original position of equilibrium and vertical lines to represent the moment of system change makes it clearer to read. + +Increasing the **temperature** of a system causes it to shift in favour of the **endothermic** side, and vice versa. + +Of the three changes, this is the only one that would change $K_c$ as it changes the rate constants, which are temperature-specific ($K_c\propto\frac{r_\text{reverse}}{r_\text{forward}}$). Therefore, as temperature **increases**, $K_c$ also **increases**, and vice versa. + +!!! example + If heat is added to a solution of KCl, more KCl will dissolve to minimise the change in temperature as it is an endothermic process. + +Increasing the **concentration** of a reactant or product will cause the position to shift **away** from the increased side, and vice versa. + +??? example + If there is an **instantaneous** spike of $\ce{N2}$ to a system at equilibrium, it will be consumed along with $\ce{H2}$ to form $\ce{NH3}$, **but not enough to return to its original value**. + + (Source: Kognity) + + The same applies if instead $\ce{NH3}$ is reduced. + + (Source: Kognity) + +Increasing the **pressure** of a gas will cause the position to shift in whatever direction would **decrease** the total moles of gas. + +!!! warning + Inert (uninvolved in a reaction) gases such as catalysts will not affect the position of equilibrium as it does not affect the **partial pressure** of the gas. In a similar vein, adding water to an aqueous solution will not cause any changes in equilibrium position. + +!!! warning + If given a system not at equilibrium, if a change is made that would change the prior equilibrium, it should be assumed that the system reaches equilibrium before the change is made, regardless if it is specified. + ## Organic chemistry !!! definition