Lesson 10 - Chemical Reactions
Student Performance Objectives1. Use simple equations to describe the following types of chemical reactions: synthesis, decomposition, exchange, reversible and redox reactions. 2. Explain the effects of the following factors on the rate of chemical reactions: substrate concentration, presence of catalysts, temperature, pH and presence of inhibitors.Lesson OutlineA. Concepts 1. Making and breaking chemical bonds (i.e., covalent or ionic). 2. Reactants and products. 3. Equations and directional arrows.B. Basic types of reactions See: http://www.wisc-online.com/objects/index.asp?objID=AP13004 1. Syntheses: A + B ? AB. a. Synthesis of cellular proteins from amino acids For a view of the formation of NaCl from its elements, see https://www.youtube.com/watch?v=lhC42qxk5kQ
b. Synthesis of liver glycogen from glucose. c. DEMONSTRATION: synthesize FeS from elemental iron and elemental sulphur. The point is to demonstrate that a chemical change produces a new substance differing in chemical composition and physical characteristics from the reactant substances. One gram of iron powder and one gram of sulfur powder are observed by students for physical qualities such as magnetic attraction, color, and odor. Then 5g S powder is placed in the bottom of a pyrex test tube and 7g of Fe powder is poured in over it. The tube is attached to a ring stand, the tube tilted away from people, everyone has safety goggles, and the tube is heated gently and uniformly with a Bunsen burner. Have the students observe closely what happens as the sulfur (turns red) melts and the Fe falls into the sulfur. As the chemical reaction occurs as evidenced by the glowing of the reaction mixture, stop heating it. When the tube cools break it open with a hammer and observe the physical characteristics of the new substance, FeS. 2. Decomposition: AB ? A + B a. Digestion of starch into glucose. b. Digestion of Triglycerides into fatty acids and glycerol. c. Point out that the electrolysis of water was a decomposition reaction. 3. Exchange: AB + CD ? AD + BC E.g., Buffering of hydrochloric acid by sodium bicarbonate in the duodenum. HCL + NaHCO3 ? H2CO3 + NaCl 4. Reversible: A + B ? C + D a. The operation of the bicarbonate buffer system in the blood. H2O + CO2 ? H2CO3 ? H+ + HCO3- b. Concept of equilibrium 5. Oxidation-reduction (redox): AH + B ® A+ + BH a. Oxidation is the loss of an electron (and often a hydrogen) by a molecule. b. Reduction is the gain of an electron (and often a hydrogen) by a molecule. c. Oxidation and reduction occur at the same time. d. Refer to the transfer of an electron from Na to Cl in the formation of Na+ and Cl- as a redox reaction. e. Also, explain that the formation of useful energy (energy currency) by cells (in mitochondria) involves the transfer of electrons from one molecule (enzyme complex) to another in sequential oxidation-reduction reactions. C. Reaction Rates are influenced by many factors. 1. Concentration of substances (substrates) taking part in the reaction. 2. Presence of enzymes or other types of catalysts (define, if necessary). 3. Temperature: note that the iron-sulfur demonstration required heat to initiate. 4. pH 5. Presence of enzyme inhibitors (e.g., heavy metals, cyanide, organic compounds).