Chemical Reactions

How Do We Know a Reaction Has Taken Place? There are often clues that let us know when a chemical reaction is taking place. Let’s do a lab to find out what some of these clues are. Some clues are: Gets hot (exothermic) Gets cold (endothermic) Releases gas (bubbles) Color change Smell change

Reactions Can Occur at Different Speeds How do the following affect the rate of a reaction? Temperature? Concentration? Surface Area? Let’s do a lab to find out!

As the temperature increases, the reaction occurs faster. This occurs because the molecules are moving faster, and “run” into each other sooner As the concentration decreases, the reaction occurs slower. This occurs because there are less molecules to “run” into As the surface area increases, the reaction occurs faster. This occurs because there are more exposed atoms to react with.

There are 5 Main Types of Reactions Synthesis (Composition) Decomposition Single Replacement (Displacement) Double Replacement (Displacement) Combustion

Synthesis When two or more substances combine to form a single substance A + B  AB 2H2 + O2  2H2O

Decomposition One compound is broken down into two or more substances. AB  A + B 2AgO  Ag2 + O2

Single Replacement One element takes the place of another in a compound. If it is a metal, it will replace the metal, if it is a nonmetal, it will replace the nonmetal A + BC  AC + B Fe + CuSO4  FeSO4 + Cu

Al Na Cl  + + SR Animation The single metal trades places with the metal in the compound. Al Na Cl  + +

Double Replacement The positive portions of two ionic compounds are swapped. AB + CD  AD + BC Pb(NO3)2 + 2KI  PbI2 + 2KNO3

Na Cl + K F  + DR Animation The positive ion of one compound now bonds to the negative ion of the other compound and vice versa Na Cl + K F  +

Combustion A hydrocarbon combines with oxygen to form carbon dioxide and water. CxHy + O2  CO2 + H2O 2C2H2 + 5O2  4CO2 + 2H2O

Practice! Composition 2H2 + O2  2H2O _____________ 6K + B2O3  3K2O + 2B _____________ HCl + NaOH  NaCl + H2O _____________ 4C + S8  4CS2 _____________ CH4 + O2  CO2 + H2O _____________ H2O2  H2 + O2 _____________ 3Li + AlCl3  3LiCl + Al _____________ 3Rb + P  Rb3P _____________ 2NaCl  2Na + Cl2 _____________ 4NH3 + 3O2  2N2 + 6H2O _____________ SR DR Composition Combustion Decomposition SR Composition Decomposition SR

Time for a Lab with Each Reaction!