CHEMICAL REACTIONS

Reactions  Chemical Reaction-The combining or breaking apart of matter to form new types of matter.  Take place when 2 or more molecules interact and something happens.  A chemical change must occur.  A reaction can include ions, molecules, or pure atoms.  Single reactions often happen as part of larger ones.  5 indicators of a chemical change: light, heat, gas formation, precipitate formation, change in color

 Reactant: a substance which is in a chemical reaction  Product: substance which is produced by the chemical reaction

4 Types of Reactions 4 Types of Reactions  Synthesis  Decomposition  Single Replacement  Double Replacement

Synthesis Reactions  Reactants combine to form a product  Two or more simple substances combine to form a more complex substance.  reactant + reactant product (simple) (simple) (complex) Example: hydrogen and oxygen combine to yield water 2H 2 + O 2 2H 2 O 2H 2 + O 2 2H 2 O

Decomposition Reactions  A reactant breaks up into products  A more complex substance yields 2 or more simple products  reactant product + product (complex) (simple) (simple) Example: water breaks down to yield hydrogen + oxygen 2H 2 O 2H 2 + O 2 2H 2 O 2H 2 + O 2

Single Replacement Reactions  A single uncombined element replaces another in a compound.  2 reactants yield 2 products reactant + reactant product + product reactant + reactant product + product Example: Zinc + hydrochloric acid zinc replaces hydrogen Zn + 2HCl ZnCl 2 + H 2 Zn + 2HCl ZnCl 2 + H 2

Double Replacement Reaction Parts of two compounds switch places to form two new compounds. reactant + reactant product + product reactant + reactant product + product Example: Silver nitrate combines with sodium chloride to make silver chloride + sodium nitrate AgNO 3 + NaCl AgCl + NaNO 3 AgNO 3 + NaCl AgCl + NaNO 3

Energy of Chemical Reactions  Chemical reactions always involve a change in energy.  Energy is either absorbed or released (it is not created or destroyed)

Endothermic Reactions  Endothermic Reactions: absorb energy  Example: Photosynthesis is an example of an endothermic chemical reaction. In this process, plants use the energy from the sun to convert carbon dioxide and water into glucose and oxygen. sunlight + 6CO 2 (g) + H 2 O(l) C 6 H 12 O 6 (aq) + 6O 2 (g)  This reaction absorbs 15MJ of energy (sunlight) for every kilogram of glucose that is produced

Exothermic Reactions  Release energy when they occur  Example: The reaction of sodium and chlorine yield table salt.  2Na(s) + Cl 2 (s) 2NaCl(s)  This reaction releases 411 kJ of energy for each mole of salt that is produced

Factors Affecting Chemical Reaction Rates  Reactions happen because particles collide.  Temperature: High temperatures increase rate.  Particle Size: Smaller particle size will increases rate.  Concentration: High concentration increases rate.

Name that Reaction  NaOH + KNO 3 NaNO 3 + KOH Double displacement  2Fe + 6NaBr 2FeBr 3 + 6Na Single displacement  Pb + O2 PbO 2 Synthesis  Na2CO3 Na 2 O + CO 2 Decomposition