PCC - Chemical Changes Lesson

 

Chemical Changes

As mentioned in the previous unit, some minerals in rocks can react with air - or waterborne substances. Chemical reactions change minerals in the rocks in which they are found, which can strengthen or weaken the rocks themselves. There are several general classifications of chemical reactions in rocks: carbonation, oxidation, and hydrolysis reactions.

Complete the surface area to volume activity below:

The chemical reaction between carbonic acid in rainwater and the calcium carbonate in limestone is a good example of how rocks can literally be "dissolved" away. The carbonation reaction actually involves a couple of steps: first, rainwater must dissolve carbon dioxide from the atmosphere to become acidic. Then, the carbonic acid reacts with the calcium carbonate (also known as "calcite") to break down the limestone into two substances that can dissolve in water.

Another example involves the oxidation of iron deposits in rocks. When iron encounters oxygen, the two will combine to form iron oxide (also known as rust). Since iron oxide is not nearly as strong as iron, the oxidation of iron can weaken rocks that contain iron, helping to set the stage for mass wasting events.

The final type of chemical weathering is known as hydrolysis ("hydro-" means "water" and "lysis" means "to cut"). Certain minerals, such as feldspar can be broken down at the molecular level by water molecules; when the feldspar is hydrolyzed, clay minerals and quartz are produced.

 

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