Accel. Chem. Blog 4

                As we come to the end of another chapter in Accelerated Chemistry, I can safely say that this class has probably challenged and pushed me more than my other classes this year.  In our latest unit, we have covered: balancing equations, types of reactions, and reactivity.  These all relate to the overall theme of chemical equations, which builds off of the last chapter, which was about charges in atoms and molecules, where we began to look at how elements are bonded together.

            We started the unit with balancing chemical equations.  The reason we do this is to follow the law of conservation of matter.  It is easy enough to write out a reaction, but you may end up with more of an atom on one side of the reaction, and that defies the law, because you either created to destroyed matter.  First, you make sure that you have written the correct formula, paying attention to charges and diatomic particles.  Then, you need coefficients to ensure that there are equal numbers of the same atoms on both sides.  We also learned some tips to help us in balancing: 1) Adjust the coefficient of a single species (ex. O₂) last.      2) Temporary (key word: TEMPORARY!) use of a fraction or decimal is helpful.  3) If there are polyatomic ions on both sides of the reaction arrow, you should balance them as groups.  To help teach idea of balancing equations, we used models of atoms to put them together and learn about the use of coefficients.

            Next, we learned about the types of chemical reactions.  To learn about this, we performed a series of labs.  There are five types of reactions: Synthesis/Combustion, Decomposition, Single Replacement, Double Replacement, and Combustion.  A synthesis reaction will produce one product. (ex. 2Na + S à Na₂S)  A decomposition reaction will begin with one reactant, but will end with two products, so it’s basically the opposite of a synthesis reaction.  Single replacement begins with an element and a compound, and ends with an element and a compound, but the elements are switched. (ex. 2Li + MgCl₂ à 2LiCl + Mg)  The metal has to react with the compound.  Double replacement basically switches around the elements.  It begins and ends with two compounds.  (ex. 2AgNO₃ + CaCl₂ à 2AgCl + Ca(NO₃)₂)  The last reaction is combustion which is just to burn.  You are always going to end up with Carbon Dioxide and Water, and all you have to do is make sure that the reactant side has O₂ and that the equation is balanced in the end.

            Lastly, we learned about reactivity, because not all elements can react.  There are a few rules when it comes to reactivity.  The main rule is that if an element is above another on the list, it will react with it, but not the other way around.  For example, Barium will react with Tin, but Chromium will not react with Calcium.  (ex. Zn + CuSO₄ à ZnSO₄ +Cu)  Another rule is that all metals about Hydrogen displace Hydrogen from HCl or H₂SO₄.  (ex. Mg + H₂SO₄ à MgSO₄ + H₂)  Another is that metals above Magnesium displace Hydrogen from water.  (ex. Fe + H₂O à no reaction)  Finally, metals above Silver on the list combine directly with Oxygen in a synthesis reaction.  (ex. Pt + O₂ à no reaction)

            A “real life example” of balancing equations is in cooking.  If you have a recipe that calls for two eggs for every three cups of flour, if you put in four eggs, you need to put in six cups of flour.  Another real life application is in a combustion reaction, the fact that you need O₂ in the equation.  I knew that you need oxygen to have a fire, but it is interesting to see that shown in what we are doing with chemical equations. 

            Our work with chemical equations originally proved to be difficult for me, but over the course of the unit I have gained deeper understanding and appreciation for the process.  Balancing equations, knowing the type of reaction, and using the activity series to solve these scientific puzzles is a vital part of chemistry and I am glad for what I have learned in this unit.