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13.1 Chemical Equilibria
A chemical reaction is usually written in a way that suggests it proceeds in one direction, the direction in which we read, but all chemical reactions are reversed depending on conditions.
If we run a reaction in a closed system so that the products can't escape, we often find the reaction doesn't give a 100% yield.
After the concentrations stop changing, some reactants remain.
When there is no change in concentrations of reactants and products, the reaction is at equilibrium.
There is a mixture of reactants and products.
Both N2O4 and NO2 are present when the system reaches equilibrium.
A mixture of NO2 and N2O4 is moving.
N2O4 forms brown NO2.
The color of the mixture changes as the reaction proceeds toward equilibrium.
All reactions are irreversible, but many of them can be done in one direction until the reactants are exhausted and can be reversed under certain conditions.
A one-way arrow from reactants to products is depicted in such reactions.
The formation of NO2 from N2O4 is one of many reactions that can be reversed under more easily obtainable conditions.
The reactants can combine to form products and the products can react to form the reactants.
The NO2 produced can react to form N2O4.
As soon as the forward reaction produces any NO2, the reverse reaction begins and NO2 starts to form N2O4.
The rate of formation of NO2 is exactly the same as the rate of consumption, so the concentrations of N2O4 and NO2 have not changed.
There is an illustration of dynamic equilibrium provided by these jugglers.
Each throws clubs at the other at the same rate.
juggler clubs are thrown continuously in both directions, and the number of clubs each juggler has at a given time remains constant.
In a chemical equilibrium, the forward and reverse reactions continue to occur at the same rate, leading to constant concentrations of the reactants and products.
Concentrations of reactants and products don't seem to change, so we can detect a state of equilibrium.
We need to verify that the absence of change is due to equilibrium and not to a reaction rate that is very slow.
A double arrow is used when writing an equation.
It is possible that such a reaction is not at equilibrium.
The discovery of a method of making carbonated water was made by Joseph Priestley in 1767, which is when the connection between chemistry and soft drinks began.
It's a great way to describe the dripping oil of sulfuric acid, "oil of vitriol" literally means "liquid nastiness" on chalk.
The resulting CO2 falls into the container of water beneath the vessel in which the initial reaction takes place.
The water has carbon dioxide in it.
As carbon dioxide reacts with water to form carbonic acid, there is an equilibrium reaction.
Carbonic acid is a weak acid and can cause hydrogen carbonate ionization.
A cascade of equilibrium shifts occurs when you open the beverage container.
The equilibrium of gas-phase CO2 and dissolved CO2 to shift is caused by the CO2 gas in the air space on top of the bottle escaping.
Less CO2 dissolved in the liquid leads to carbonic acid decomposing to dissolved CO2 and H2O.
The final equilibrium is shifted by the lowered carbonic acid concentration.
As long as the soft drink is in an open container, the CO2 bubbles up out of the beverage, releasing the gas into the air.
Equilibrium shifts occur when a soft drink is opened.
The second example of a system at equilibrium is the evaporation of bromine.
When we pour liquid bromine into an empty bottle, the amount of liquid decreases and the amount of Vapor increases.
If we cap the bottle so no vapor escapes, the amount of liquid and Vapor will eventually stop changing and an equilibrium between the liquid and the Vapor will be established.
The equilibrium would not be reached if the bottle were not capped.
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