CHEM1001 Lecture Notes - Lecture 12: Solution, Egg White

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1 Aug 2016
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Lecture 12
Chemical changes are also known as chemical reactions.
The "Ingredients" of a reaction are called the reactants, and the end results are called
the products.
The formation of gas bubbles is often the result of a chemical change.
A chemical change might also result in the formation of a precipitate, such as the
appearance of a cloudy material when dissolved substances are mixed.
Rotting, burning, cooking, and rusting are all further types of chemical changes because
they produce substances that are entirely new chemical compounds.
Burned wood becomes ash, carbon dioxide, and water.
When exposed to water, iron becomes a mixture of several hydrated iron oxides and
hydroxides.
Yeast carries out fermentation to produce alcohol from sugar.
An unexpected color change or release of odor also often indicates a chemical change.
The color of the element chromium is determined by its oxidation state; a single
chromium compound will only change color if it undergoes an oxidation or reduction
reaction.
The heat from cooking an egg changes the interactions and shapes of the proteins in the
egg white, thereby changing its molecular structure and converting the egg white from
translucent to opaque.
The best way to be completely certain whether a change is physical or chemical is to
perform chemical analyses, such as mass spectroscopy, on the substance to determine
its composition before and after a reaction.
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