Reaction between the mineral calcite (CaCO3) and carbonic acid (H2CO3): The reaction continues until a new equilibrium state is reached between the amount of carbon dioxide gas (CO2) in the atmosphere and the water raindrop. That is, the amount of carbon dioxide gas (CO2) in the water raindrop, or beaker of water, increases because more carbon dioxide gas (CO2) is pushed into, or is dissolved into, the water (Photo 3). If we increase the pressure of carbon dioxide gas (CO2) in the atmosphere, then reaction adjusts by pushing the reaction "forward", to the right. Influence of carbon dioxide (CO2) pressure: If we change the temperature or the pressure of the atmosphere or the water, the ratio of CO2 gas dissolved in the water will also change. At equilibrium, the amount of CO2 gas in the water remains the same so long as the temperature and the pressure don’t change. Simultaneously, a small amount of the dissolved CO2 escapes back into the atmosphere. That CO2 exchange continues back and forth between the air and water until a steady state, or equilibrium, is reached. Said differently, a small amount of CO2 gas from the atmosphere gets dissolved in the water. When a water raindrop falls through the atmosphere, CO2 gas distributes itself between the water raindrop and the atmosphere. The symbol means CO2 gas moves back and forth between the atmosphere and the raindrop. That reaction is written:ĬO2 in the air CO2 dissolved in water Let’s apply the reaction notation to describe a relationship between carbon dioxide gas (CO2) and water (H2O). Our atmosphere consists mostly of nitrogen gas (N2) and oxygen gas (O2), but it also contains a small amount of carbon dioxide gas (CO2). Carbon dioxide (CO2) dissolved in water (H2O): Chemists use the word “partition” to describe the distribution of a component, such as CO2, between air and water. One way to understand how the mineral calcite (CaCO3 ) behaves at, or near, the surface of the Earth, is to consider how carbon dioxide gas (CO2 ) distributes itself between the atmosphere, or soil gas, and water (H2O). Chemical equilibrium is the state of a reversible chemical reaction in which there is no net change in the amounts of reactants and products. Chemists also use the term chemical equilibrium. The chemical reaction can go “forward” (left to right) or it can go in the “reverse” direction (right to left), depending if, or how, we change the conditions affecting the reaction or if a steady state. The reaction proceeds in the “forward reaction direction”, from left to right.Īlternatively, we can write the chemical equation such that it shows the reaction moving in the reverse direction, or from right to left: That means reactants A and B react together to produce products C and D. The reaction is written in a way with the arrow pointing to the right, “=>”. For example, using the imaginary chemical reaction: A chemical reaction can move in either direction, depending on the conditions. Reaction directions:Īn important convention used by chemists is the direction that a chemical equation moves. Chemists define A and B as the reactants and C and D as the products. Means components A and B react together to produce products C and D. The reaction equation describes what happens when components on one side of the equation react together to form components on the other side of the equation. Increasing the water temperature decreases the amount of CO2 dissolved in water and causes calcite to precipitate ĭecreasing the water temperature increases the amount of CO2 dissolved in water and causes calcite to dissolve.Ĭhemists describe a chemical reaction using reaction equations. Increasing the pressure of CO2 gas in a system causes calcite to dissolve and go into solution ĭecreasing the pressure of CO2 gas in the system causes calcite to precipitate from solution
In case you don’t want the read about the chemical reactions that describe the stability of calcite (CaCO3), carbon dioxide gas (CO2), and water (H2O), here are the four important “take-aways”: Although my synthesis is very simple, it is a place to start to understand some of the geological, physical, and chemical factors that may have played a role in the formation of some calcareous habitats. The chemistry controlling the formation of calcareous habitats can be very complex. That, in turn, helps us understand the location and physical features of some calcareous habitats and the types and distributions of flora that live in this unusual habitat. Understanding the geological and geochemical processes that lead to precipitation, or dissolution, of calcite help us understand the chemical steps that create calcareous habitats. They are home to some unusual flora, birds, and insects.
Calcareous habitats are unusual and uncommon. Calcite is the main calcium-bearing mineral that occurs in calcareous habitats.
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