Chemical Reactions Different Types of Reactions

Review/Remember: What’s the difference between a Physical and Chemical Change?

Physical Change: Changes the way something looks Chemical Change: Changes the chemical makeup of the substance (it makes something new!) Can’t be undone or reversed by physical changes Indicators of a chemical change: 1. light 2. Heat 3. Gas (bubbles) 4. Color change 5. Precipitate (formation of a solid from liquids)

Occur when substances undergo chemical changes to form new substances. Chemical Reactions CHEMICAL REACTIONS Occur when substances undergo chemical changes to form new substances. Atoms are rearranged (NOT created or destroyed). Parts of a Reaction Reactants Substance or molecule that participates in a chemical reaction. On left side of arrow in chemical equation Products Substance that forms in a chemical reaction. On right side of arrow in chemical equation 2H2 + O2  2H2O (Reactants) (Products)

CHEMICAL BONDS BETWEEN ATOMS (Ionic and Covalent) Chemical Reactions CHEMICAL BONDS BETWEEN ATOMS (Ionic and Covalent) Sometimes energy must be added to break bonds so atoms can be rearranged. Activation energy = energy required to begin or finish a reaction Many forms of energy can be used to break bonds such as heat, light, electricity, and sound. Often forming bonds releases energy (like explosions).

Activation Energy

CONSERVATION OF ENERGY AND MASS Chemical Reactions CONSERVATION OF ENERGY AND MASS Mass and energy are conserved in chemical reactions. The total energy and mass that exists before the reaction is equal to the total energy and mass of the products and their surroundings. HEAT AND CHEMICAL REACTIONS Exothermic reaction = chemical reaction in which heat is released to the surroundings. Endothermic reaction = chemical reaction that absorbs heat

Chemical Reactions SPEED OF A REACTION CATALYST = substance that changes the rate of a chemical reaction without being consumed or changed significantly. Catalysts are not reactants or products, because they are not used up in the reaction. Catalysts are often used in industry to make reactions go faster (saves money and time). Catalyst in your body are called enzymes

Types of Reactions

#1 Reaction Synthesis Reaction A + B  AB 2Na + Cl22  2NaCl Chemical Reactions Synthesis Reaction Two or more substances combine to form a new compound. Synthesis reactions have the following general form: A + B  AB Example: 2Na + Cl22  2NaCl

Decomposition Reaction Chemical Reactions Decomposition Reaction A single compound breaks down to form two or more simpler substances. Decomposition reactions have the following general form: AB  A + B Example: 2H2O  2H2 + O2

Single-Displacement Reaction Chemical Reactions Single-Displacement Reaction One element or ion takes the place of another element or ion in the compound. Single-displacement reactions have the following general form: AX + B  BX + A Example: 3CuCl2 + 2Al  2AlCl3 + 3Cu

Double-displacement Reaction Chemical Reactions Double-displacement Reaction A gas, a solid precipitate, or a molecular compound forms from the apparent exchange of atoms or ions between two compounds. Double-displacement reactions have the following general form: AX + BY  AY + BX Example: Pb(NO3)2 + K2CrO4  PbCrO4 + 2KNO3

#5 Reaction Combustion Reaction Chemical Reactions Combustion Reaction The reaction of a carbon-containing compound, in which heat is released. Combustion reactions use O2 as a reactant. H2O and CO2 is a common product of combustion reactions. Example: 2CH4 + 4O2  2CO2 + 4H2O + heat