6: Introduction to Chemical Reactions
Chemical change is a central concept in chemistry. The goal of chemists is to know how and why a substance changes in the presence of another substance or even by itself. Because there are tens of millions of known substances, there are a huge number of possible chemical reactions. In this chapter, we will find that many of these reactions can be classified into a small number of categories according to certain shared characteristics.
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- 6.1: 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.
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- 6.2: 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.
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- 6.4: Quantitative Relationships Based on Chemical Equations
- A balanced chemical equation not only describes some of the chemical properties of substances—by showing us what substances react with what other substances to make what products—but also shows numerical relationships between the reactants and the products. The study of these numerical relationships is called stoichiometry. A balanced chemical equation gives the ratios in which molecules of substances react and are produced in a chemical reaction.
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- 6.5: Types of Chemical Reactions
- This page describe "five types of chemical reactions". In reality, there is no simple schema to fit reactions into five types, and even in this class we will use other descriptions of chemical reactions. But these 5 types are very useful at this stage in the class, and they can be useful in setting up strategies for balancing chemical equations. So it is important to recognize these.
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- 6.6: Oxidation-Reduction (Redox) Reactions
- Chemical reactions in which electrons are transferred are called oxidation-reduction, or redox, reactions. Oxidation is the loss of electrons. Reduction is the gain of electrons. Oxidation and reduction always occur together, even though they can be written as separate chemical equations.