Types of Chemical Reactions

First a few concepts to take into consideration… In Unit 4 we learned how bonds are formed from elements, called compounds. In Unit 5 we will learn how those compounds form together through a process called a chemical reaction

a process in which one or more substances change to make one or more new substances. Baking bread, a space shuttle launch, & eating lunch are all examples of this What is a Chemical Reaction?

What Are Some Signs of Chemical Reactions? Cu(s) + 4HNO 3 (aq)  Cu(NO 3 ) 2 (aq) + 2NO 2 (g) + 2H 2 O

What Are Some Signs of Chemical Reactions? 2 AgNO 3(aq) + K 2 CrO 4(aq)  Ag 2 CrO 4(s) + 2 KNO 3(aq)

What Are Some Signs of Chemical Reactions?

How do you know a “Chemical” Reaction has taken place? The MOST important sign The formation of a new substance with different properties Sugar reacting with sulfuric acid The product is neither sugar nor acid

Sulfuric Acid Reacting with Sugar C 12 H 22 O H 2 SO 4 12C + 11H 2 SO H 2 O SolidLiquidSolidGas

Issues To Consider Formulas show chemistry at a standstill Equations show chemistry in action Every chemical compound has a formula which cannot be altered A reaction must account for EVERY atom used –The Law of Conservation of Matter

Types of Chemical Reactions you NEED to know! - 4 Types-

Reaction #1 - Synthesis Two or more elements combine to form a single, more complex compound The Basic Form: A + B  AB The following are examples of synthesis reactions

Synthesis Reactions 2Mg + O 2 → 2MgO C + O 2 → CO 2 2Na + Cl 2 → 2NaCl MgO + H 2 O → Mg(OH) 2

Reaction #2 - Decomposition A single compound breaks down into its component parts The Basic Form: AB  A + B The following are examples of decomposition reactions

Decomposition Reactions CaCO 3 → CaO + CO 2 2KClO 3 → 2KCl + 3O 2 H 2 SO 4 → H 2 O + SO 3 2NaCl → 2Na + Cl 2

Reaction #3 - Single Replacement/Displacement A more active element takes the place of another element in a compound & sets the less active one free. The Basic Form: A + BC  AC + B The following are examples of single replacement/displacement reactions

Single Replacement/displacement Reactions Fe + CuSO 4 → FeSO 4 + Cu 2Mg + 2H 2 O → 2MgO + 2H 2 2Na + 2H 2 O → 2NaOH + H 2 Cl 2 + 2NaBr → 2NaCl + Br 2

Reaction #4 - Double Replacement/Displacement Also called an Ionic Reaction A reaction will occur when a pair of ions come together and change places. –Sometimes called an Ionic Reaction The Basic Form: AB + CD  AD + CB The following are examples of single replacement/displacement reactions

Double Replacement/displacement Reactions BaCl 2 + Na 2 SO 4 → 2NaCl + BaSO 4 2HCl + FeS → FeCl 2 + H 2 S NaCl + AgNO 3 → NaNO 3 + AgCl HCl + NaOH → NaCl + H 2 O

Sec. 4: Energy and Rates of Chemical Reactions Chemical Reactions have energy going in one of two directions Going outward – Exothermic –Using energy –Releasing energy –The amount of energy when finished is less than when you started.

Exothermic Reactions

More Exothermic Reactions… Energy released in an exothermic reaction is often written as a product in the balanced chemical equation. 2Na + Cl 2  2NaCl + energy This reaction continues to emphasize the Law of Conservation of Matter/Mass.

Exothermic Reaction Diagram

Energy and Rates of Chemical Reactions Chemical Reactions have energy going in one of two directions Going inward - Endothermic –Energy taken in –Storing energy –The amount of energy when finished is more than when you started.

An Endothermic Reaction Photosynthesis is a great example of storing energy!

More Endothermic Reactions… Energy that is taken in during an endothermic reaction is often written as a reactant in a chemical reaction. Photosynthesis 6CO 2 + 6H 2 O + energy  C 6 H 12 O 6 + 6O 2 This reaction continues to emphasize the Law of Conservation of Matter/Mass.

Endothermic Reaction Diagram

What is the Law of Conservation of Energy? Energy cannot be created or destroyed. However it can change forms. Energy can be transferred –Conduction, Convection, & Radiation The total energy before a reaction will be the same as the total energy after the reaction.

What is the “Rate” of a Chemical Reaction? A chemical reaction takes place when particles collide with enough force to break bonds. The speed at which new particles form is called the “rate of a reaction”

What is Activation Energy? The smallest amount of energy molecules need to react. For example: –Matches have two chemicals on them that will ignite to create a flame (exothermic reaction) –However, those chemicals require energy to activate them - striking the match with friction.

Sources of Activation Energy? Friction Electricity - spark Light Motion Anything that transfers energy

What Factors Affect the Rate of Reactions? Temperature –High temperatures = increased rate of reaction Concentration –High concentration = increased rate of reaction Surface Area –Greater surface area = increased rate of reaction Inhibitors –A substance that slows down the rate of reaction Catalysts –A substance that speeds up the rate of reaction

What is an Inhibitor? A substance that decreases the rate of a reaction Examples include: –Food preservatives –Some antibiotics –Cement setting inhibitors to prevent cement from drying too quickly

What is a Catalyst? A substance that increases the rate of reaction with LESS energy. Examples include: –Catalytic converter on cars –Some glues use a catalyst to harden the glue