Section 2: Types of chemical reactions  There are 4 different types of chemical reactions: 1. Synthesis 2. Decomposition 3. Single replacement 4. Double.

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Creating compounds Two or more reactants combine together to produce one type of compound A + B AB Examples *Rust *Haber Process

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  • 1 Section 2: Types of chemical reactions  There are 4 different types of chemical reactions: 1. Synthesis 2. Decomposition 3. Single replacement 4. Double replacement
  • 2 Synthesis  Synthesis= 2 elements combine to form a single compound Example: 2Na + Cl 2 2NaCl
  • 3 Creating compounds Two or more reactants combine together to produce one type of compound A + B AB Examples *Rust *Haber Process
  • 4 “The Haber process is also an example of the complex impact of chemistry upon life. At the start of World War I, Germany was dependent upon the natural nitrate deposits of Chile for the nitrogen compounds required to manufacture explosives. The Allied blockade of South American ports soon cut off this supply. Had it not been for the alternative source of nitrogen compounds provided by the direct synthesis of ammonia, Germany most likely would have been forced to surrender several years before 1918. By prolonging the war, the Haber process indirectly cost thousands of lives. However, over the years, the fertilizer produced by the same process has increased crop yields around the globe and spared millions from starvation.” “Although now modified and improved, the Haber process continues to be the most common method for making ammonia. The nitrogen is obtained from liquefied air, and the hydrogen is usually from natural gas decomposed by heating.”. www.scifun.org Synthesis Reaction
  • 5 Decomposition  Decomposition= a compound breaks down to form 2 or more substances Example: H 2 CO 3 H 2 0 + CO 2
  • 6 B Single compound breaks down into 2 or more products Examples 1) 2 H 2 O 2 H 2 + O 2 2) Carbonic acid in soda
  • 7 Decomposition Reaction
  • 8 Single replacement  Single replacement- a new element takes the place of another element that is already part of a compound * More reactive elements replace less reactive elements Example: Zn + 2HCl ZnCl2 + H2
  • 9 B The reactants are an element and a compound Free element replaces another element that is part of a compound AC B B B C C AB + C AC + B ABC A AA C C C AB + C CB + A C
  • 10 Single Replacement Reaction
  • 11 Double replacement  Double replacement= elements in 2 compounds switch places *One of the products is often a gas or precipitate (solid) Example: NaCl + AgF NaF + AgCl
  • 12 2 elements in different compounds replace each other AB CD A AA A C CC AB + CD --> CB + AD C NaCl (aq) + AgNO 3(aq) NaNO 3(aq) + AgCl (s)
  • 13 Double Replacement Reaction
  • 14 Review!
  • 15 a.2MgO  b.2Li + MgSO 4  c.3KOH + FePO 4  d.2Ca + O 2  Only one compound, so it must be decomposition Mg + O 2 2 Compound and element = single replacement Li 2 SO 4 + Mg Two compounds so it is double replacement K 3 PO 4 + Fe(OH) 3 2 elements, so it is synthesis CaO 2
  • 16 Review Questions! 1. What type of reaction does each of the following equations represent? a) FeS + 2 HCl  FeCl 2 + H 2 S b) NH 4 OH  NH 3 + H 2 O 2. Which type of reaction always has an element and a compound as reactants? 3. What is the difference between synthesis and decomposition?
  • 17 Every Reaction Involves Energy!  REMEMBER, during a chemical bond:  If chemical bonds are broken, energy is absorbed!  If chemical bonds form, energy is released!
  • 18 Energy is released in exothermic reactions!  If the chemical energy of the reactants is greater than the chemical energy of the products, energy is released.  We call this EXOTHERMIC! (exo means exit)  Energy will be written on the product side (right side) of the arrow EXAMPLE: 2 Na + Cl 2 2 NaCl + energy
  • 19 Types of energy that can be released!  3 types of energy can be released:  Light energy  Electrical energy  Light & thermal (heat) energy
  • 20 Exothermic Energy Diagram
  • 21 Energy is absorbed in endothermic reactions!  If the chemical energy of the reactants is less than the chemical energy of the products, energy is absorbed!  We call this ENDOTHERMIC (endo means go in)  Energy will be written on the reactant side (left side) of the arrow EXAMPLE: 2 H 2 O + energy 2 H 2 + O 2
  • 22 Endothermic Energy Diagram
  • 23 Energy is always conserved!  Law of conservation of energy- energy cannot be created nor destroyed
  • 24 Activation energy gets a reaction started!  Activation energy= the minimum amount of energy needed for substances to react
  • 25 Factors affecting rates of reactions: 1. Temperature (increase temp, increase rate) 2. Surface area (increase surface area, increase rate) 3. Concentration (increase concentration, increase rate) 4. Presence of a catalyst or inhibitor catalyst= speeds up a reaction, lowers activation energy Inhibitor= slows down or stops reaction
  • 26 Review Questions! 1. What is activation energy? 2. List 4 ways to increase the rate of a reaction. 3. Compare endothermic and exothermic reactions. 4. Does this energy diagram show an endothermic or exothermic reaction? How do you know?
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