Types of Chemical Reactions There are 4 common types of chemical reactions and one special type you will soon know by sight and by description.
Types of Chemical Reactions - Synthesis • When you bake a cake, you are creating a single product from more than one ingredient. That is synthesis. • Synthesis also describes a type of reaction in which a single product, a compound, is made from multiple reactants. • The equation A + B AB is a way to represent synthesis.
Types of Chemical Reactions - Synthesis • The way to recognize a synthesis reaction equation is that it always has just a single product. • 2H2 + O2 2H20 is a synthesis reaction. • How can you tell it is synthesis? • Can the product of a synthesis reaction be an element?
Types of Chemical Reactions - Synthesis • Water and dinitrogen pentoxide react to produce aqueous hydrogen nitrate. • Let’s write the chemical equation for that reaction. • Write the formula for water first, followed by a “+” sign. • Dinitrogen pentoxide is a covalent compound, as you can tell by the prefixes. Its formula is… • Come on, how many nitrogens and how many oxygens? • Write it on your paper. Then write the arrow. • Hydrogen nitrate is an ionic compound, as you can tell by the ate suffix. Make sure you balance the charges when you figure out its formula.
Types of Chemical Reactions - Synthesis • Water + dinitrogen pentoxide hydrogen nitrate. • H2O + N2O5 HNO3 • Did you get that? If not, figure out why. If so, you are on the right track! • Now balance the equation. It’s not finished, unless it is balanced, as the law of conservation of matter must be satisfied.
Types of Chemical Reactions - Synthesis H2O + N2O5 2HNO3 In this reaction, two compounds reacted to make a new compound. Because there is only one product, the reaction is • SYNTHESIS!
Types of Chemical Reactions - Decomposition • If you have ever watched CSI or Dr. G, Medical Examiner on television, you have probably heard a lot of talk about decomposition. • Decomposition is the breaking down of a substance into simpler substances. • A compound can break down into elements, simpler compounds, or a combination of those. • Can an element decompose? • No, it can’t, as an element is the simplest kind of substance.
Types of Chemical Reactions - Decomposition • AB A + B is an equation commonly used to represent decomposition. • You can recognize a decomposition reaction because it has only one reactant, which is always a compound. • On which side are reactants? • Reactants are on the left side of a chemical reaction.
Types of Chemical Reactions - Decomposition • By using electrolysis, water can be broken down into hydrogen gas and gaseous oxygen. (Those gas-related terms mean the same thing.) • Write the equation that represents that reaction. • I’m not kidding – write it down. • Don’t think I’m going to give you something that easy. • Did you balance it yet?
Types of Chemical Reactions - Decomposition • 2H2O 2H2 + O2 • We could add the (l) and (g) to show the states of matter, but we’ll keep it simple for now. If you are asked for a complete chemical reaction, the states of matter must be included. • Observe the characteristics of that reaction that identify it as decomposition.
Types of Chemical Reactions - Decomposition • Nickel-II hydroxide decomposes to produce nickel-II oxide and water. • Write the chemical equation. The nickel-II has a charge of… • +2 (The Roman numerals are used with transition metals to tell what charge they have, and metals always make positively charged ions.)Use that information to correctly write the formula for the nickel-II compounds.
Types of Chemical Reactions - Decomposition • Nickel-II hydroxide nickel-II oxide + water • Ni+2 OH- Ni+2 O-2 + H2O • Ni(OH)2 NiO + H2O • Check for balance. Note the characteristics of that reaction that indicate that it is decomposition.
Types of Chemical Reactions – Single Replacement • Single replacement reactions are also known as single displacement reactions, because one member of a pair is displaced/replaced. • An analogy: Al and Betty are dancing and Chad is standing by. When the opportunity arises, Chad cuts in, taking over as Betty’s dance partner and leaving Al out. Chad replaced Al in the compound (dancing couple). • AB + C CB + A represents a single-replacement reaction.
Types of Chemical Reactions – Single-replacement • A single-replacement reaction always starts with an element and a compound, and ends with a different element and compound. • The more active element will replace the less active element in a compound. • When fluorine and sodium chloride come into contact, the fluorine replaces the chlorine from the sodium chloride, making sodium fluoride, because fluorine is a more active halogen than chlorine. • F2 + 2NaCl 2NaF + Cl2 • Element + compound compound + element
Types of Chemical Reactions – Single Replacement • How do we know which elements are more or less active? • We use a tool called an activity series. • An activity series is a list of elements, usually metals, but sometimes halogens, in order from most to least active. • Hydrogen is sometimes included on a activity series, because it forms bonds like a metal, as it forms a 1+ ion.
Copy this activity series onto your paper. Which is more active, copper or magnesium? Would lead replace silver in a compound? Find the 3 most active and the 3 least active metals on your periodic table of elements. Types of Chemical Reactions – Single Replacement
Predict whether a single-replacement reaction will occur: K + ZnCl2 Fe + Na3PO4 Mg + AlCl3 Check your activity series to determine if the single element is more active than the one in the compound. Yes, the potassium will replace the zinc. (A metal can only replace a metal.) No, the iron is less active than the sodium, so no reaction will occur. Yes, the magnesium is more active than aluminum, so it will replace the aluminum. Types of Chemical Reactions – Single Replacement
Now lets complete the chemical equations for the reactions that do happen. K + ZnCl2 Mg + AlCl3 Make sure your metals only change places with metals. KCl + Zn MgCl2 + Al Types of Chemical Reactions – Single Replacement
Types of Chemical Reactions – Single Replacement • Now balance the equations! • 2K + ZnCl2 2KCl + Zn • 3Mg + 2AlCl3 3MgCl2 + 2Al
Types of Chemical Reactions • If you have been having difficulty writing the chemical formulas (for each compound) or balancing the chemical equations, go back and review those concepts. The rest of the chemistry course will be dependent upon you mastering those skills.
Types of Chemical Reactions – Double Replacement • You’ve learned about single-replacement reactions, in which the uncombined element takes the place of its counterpart in the compound. • Double-replacement reactions involve two compounds changing their pairings.
Types of Chemical Reactions – Double Replacement • Here’s a new analogy: Al and Betty are dancing. On the same dance floor are Chad and Diane. The DJ calls out, “Everyone switch!” Al and Chad switch partners, making the couples now Al and Diane, Betty and Chad. • AB + CD AD + CB
Types of Chemical Reactions – Double Replacement • AB + CD AD + CB • You can tell a double-replacement reaction has taken place because two compounds were the reactants, and two different compounds were the products. • The cation from the first compound joins with the anion from the second one. The anion from the first compound joins with the cation from the second one. They switched partners.
Types of Chemical Reactions – Double Replacement • Aluminum chloride and sodium chlorate react to form aluminum chlorate and sodium chloride. • Write the chemical equation. • Aluminum chloride is… • Sodium chlorate is… (Use your table of polyatomic ions for the chlorate.) • Aluminum chlorate is … • Sodium chloride is …
Types of Chemical Reactions – Double Replacement • I’m really not going to give you that answer. • If you are not confident about your ability to do that one, do some review, tutorial, or see me after school on Wednesday.
Types of Chemical Reactions – Combustion • Combustion is a special kind of reaction in which energy is released in the form of light and/or heat. • You know combustion as burning. • Combustion always requires oxygen gas on the reactant side. • Combustion of a hydrocarbon (look it up) always produces water and carbon dioxide. • Your study guide from part 1 of this unit includes at least two examples of combustion.
Types of Chemical Reactions – Combustion • Your body burns glucose to produce the energy your body needs. • The equation for that reaction is • C6H12O6 + O2 CO2 + H2O • How did I know that oxygen was a reactant? • How did I know what the products would be? • Balance the chemical equation.
Types of Chemical Reactions – Combustion • C6H12O6 + 6O2 6CO2 + 6H2O • Can you name all 5 types of chemical reactions without looking through your notes?
Types of Chemical Reactions – Combustion • Propane (C3H8) burns in most gas grills. You can now write the chemical equation for this reaction. • Start with propane and the other reactant. • How do you know that propane is a hydrocarbon? • You know the products. • Did you remember the arrow? • Balance the equation. • I’m not giving you the answer. If you cannot do this, you need to look into some online tutorials or get help.
Types of Chemical Reactions • Wow, this was a long presentation. • One final note: Not all chemical reactions fit these types. Sometimes, the reactants have 2 compounds and an element, or the products include 3 substances, or… • The majority of reactions you will encounter in a basic chemistry course will fit these types, and knowing the patterns will help you to predict chemical behavior.
Types of Chemical Reactions • http://www.youtube.com/watch?v=tE4668aarck • The above link will take you to an excellent little animation of the 5 types of chemical reaction. Enjoy!