Chemical Equations
chemical reaction |
process that neither creates nor destroys atoms, but that rearranges atoms in chemical compounds. involve changes in energy. |
chemical equation |
uses chemical symbols to denote what occurs in a chemical reaction. |
a chemical equation represents a chemical statement. |
reactant |
each chemical species that appears to the left of the arrow. |
substances that are consumed in the course of a chemical reaction. |
product |
each species that appears to the right of the arrow. |
substances that form during the course of a chemical reaction. |
gases, liquids, and solids are labeled with (g), (l), and (s). |
aqueous: chemical species that are dissolved in water; labeled (aq) |
some nonmetals exist as polyatomic molecules: H2, N2, O2, F2, Cl2, Br2, I2, and P4. |
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Balancing Chemical Equations
law of conservation of mass |
atoms can neither be created nor destroyed. |
stoichiometric coefficients |
numeric values written to the left of each species in a chemical equation to balance the equation. |
Calculations
stoichiometric amount |
quantity of reactant in the same relative amount as that represented in the balanced chemical equation. |
limiting reactant |
reactant used up first in a reaction, limits the amount of product that can form. |
excess reactant |
present in quantities greater than necessary to react with the quantity of the limiting reactant. |
theoretical yield |
amount of product that forms when all the limiting reactant reacts to form the desired product; maximum obtainable yield, predicted by the balanced equation (the limiting reactant produces the theoretical yield). |
actual yield |
amount of product actually obtained from a reaction; almost always less than the theoretical yeild. |
percent yield |
determines the efficiency of a chemical reaction |
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% yield = actual yield/theoretical yield (100%) |
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temperature and pressure can affect percent yield. |
atom economy |
theoretical determination of how much of the starting mass of reactants can end up in the final mass of the desired product. |
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atom economy = sum of molar mass of desired product/sum of molar masses of reactants (100%) |
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Types of Reactions
combination reaction |
two or more reactants combine to form a single product - A + B --> AB |
decomposition reaction |
two or more products form a single reactant; opposite of combination reaction - AB --> A + B |
combustion reaction |
substance burns in the presence of oxygen. produces carbon dioxide gas and water. |
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Combustion Analysis
combustion analysis |
experimental determination of an empirical formula by a reaction with oxygen to produce carbon dioxide and water. |
organic compounds |
containing C, H, and O, are carried out using an apparatus in combustion analysis. |
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