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Chemical Reactions & Equations. Chemistry SOLs 1.a; 3.b-c; 3.e-g; 4.f. The Nature of Chemical Reactions. A chemical reaction is a process in which one or more substances are converted into new substances with different physical and chemical properties.
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Chemical Reactions & Equations Chemistry SOLs 1.a; 3.b-c; 3.e-g; 4.f
The Nature of Chemical Reactions A chemical reaction is a process in which one or more substances are converted into new substances with different physical and chemical properties. (1.) (a.) Name an example of a physical reaction (b.) Name an example of a chemical reaction. (c.) What’s the difference?
Chemical reactions involve two types of substances: 1. Reactant 2. Product
Chemical Equations Chemical reactions are represented by chemical equations. Word Equations Calcium + Oxygen → Calcium Oxide Formula Equations Ca + O2→ CaO (2.) (a.) What are the reactants in each equation? You may use the words or formulas. (b.) What are the products in each equation?
Balancing Equations Since matter is neither created nor destroyed, the total mass of the reactants must equal the total mass of the products. This is known as the conservation of mass. In other words, everything on the right must equal everything on the left!
Writing Complete Chemical Equations Chemical equations not only describe how a chemical reaction actually occurs, but it also provides the physical state of the reactants and products. (s) – solid (g) – gas (l) – liquid (aq.) – solid in an aqueous solution
Classifying Chemical Reactions There are four general types of chemical reactions: 1. Direct Combination 2. Decomposition 3. Single-Replacement 4. Double-Replacement
Direct Combination (synthesis) A + B → AB Ex. 2Na + Cl2 → 2NaCl • A reaction in which two or more simple reactants join to form a single, more complex product. (3.) (a.) How many Sodium atoms are on the reactants side? (b.) How many Chlorines are on the reactants side? (c.) How many Sodium atoms are on the products side? (d.) How many Chlorines on the products side? (e.) Are they the same?
Decomposition AB → A + B Ex. 2H2O → 2H2 + O2 • A reaction in which a single complex compound is broken down into two or more products.
Single-Replacement A + BX→ AX + B Ex. Mg + Cu SO4 → MgSO4 + Cu • A reaction in which an uncombined element replaces an element that is part of a compound. • Replacement based on activity series. • Metals usually replace metals or hydrogen. • Nonmetals usually replace nonmetals.
Double-Replacement AX + BY→ AY + BX Ex. CaCO3 + 2HCl → CaCl2 + H2CO3 • A reaction in which atoms or ions from two different compounds replace each other. • Most will not occur unless the reactants are dissolved in H2O. • Will proceed if one product is a molecular compound, precipitate, or gas that cannot be dissolved in H2O.
Other Types of Reactions Combustion Reactions A combustion reaction is one in which an element or compound reacts with oxygen, producing energy in the form of heat or light as well as carbon dioxide and water. Below is the combustion reaction for benzene. 2 C6H6 + 15 O2→ 12 CO2 + 6 H2O (4.) How does this information help to explain why you can put out most fires by smothering them?
Oxidation-Reduction Reactions A reaction that involves the transfer of electrons between reactants during a chemical change. Mg + S → MgS We will go over these later!
Neutralization Reactions A reaction in which an acid and a base react in an aqueous solution to produce a salt and water. HCl + NaOH → NaCl + H2O (5.) This is a specific kind of one of the four reaction types we already covered. Which one?
