# 4: Chemical Calculations 1


• 4.1: Prelude to Introduction to Chemical Reactions
Although yeast has been used for thousands of years, its true nature has been known only for the last two centuries. Yeasts are single-celled fungi. About 1,000 species are recognized, but the most common species is Saccharomyces cerevisiae, which is used in bread making. Other species are used for the fermentation of alcoholic beverages. Some species can cause infections in humans.
• 4.2: The Law of Conservation of Matter
One scientific law that provides the foundation for understanding in chemistry is the law of conservation of matter. It states that in any given system that is closed to the transfer of matter (in and out), the amount of matter in the system stays constant. A concise way of expressing this law is to say that the amount of matter in a system is conserved. The amount of matter in a closed system is conserved.
• 4.3: Chemical Equations
Chemical reactions are represented by chemical equations that list reactants and products. Proper chemical equations are balanced; the same number of each element’s atoms appears on each side of the equation.
• 4.4: Some Types of Chemical Reactions
Although there are untold millions of possible chemical reactions, most can be classified into a small number of general reaction types. Classifying reactions has two purposes: it helps us to recognize similarities among them, and it enables us to predict the products of certain reactions. A particular reaction may fall into more than one of the categories that we will define in this book.
• 4.5: Single Replacement Reactions
• 4.6: Activity Series
• 4.7: Double Replacement Reactions
A double-replacement reaction is a reaction in which the positive and negative ions of two ionic compounds exchange places to form two new compounds.
• 4.9: The Mole
A mole is $$6.022 \times 10^{23}$$ things.
• 4.10: Molar Mass
• 4.11: Atomic and Molar Masses
The mass of moles of atoms and molecules is expressed in units of grams.
• 4.12: Mole-Mass Conversions
It is possible to convert between moles of material and mass of material.
• 4.13: Percent Composition
• 4.14: Percent of Water in a Hydrate

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