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A Chemist's Shorthand Way of Writing a Chemical Reaction Chemical Equations A Chemist’s Shorthand way of writing a Chemical Reaction. SHS ©2005, Douglas Gilliland Honors Physical Science Sarasota High, Sarasota, FL Chemical Reaction A process in which substances undergo physical and chemical changes that result in the formation of new substances with different physical and chemical Fire is energy released in an properties. exothermic reaction between substances in wood and oxygen in the air. Chemical Equation A chemical equation is a shorthand way of writing a chemical reaction using chemical symbols, formulas and coefficients. Rusting is a chemical reaction in which iron acnode fofcixhcyeiemgneitcna cl omybiienled sto yield iron(IIcIh) eomxiicdael symbol sign formula 4Fe 3O → 2Fe O + 2 diatomic 2 3 REACTANTS elemenPtRODUCT The Law of Conservation of Mass Matter cannot be created or destroyed in a chemical reaction. Atoms are simply rearranged to form new substances. Atoms and ions on Atoms and ions on the reactant side = the product side Coefficients Coefficients are whole numbers placed in front of reactants and products. They are used to balance an equation to show matter is conserved. Hydrogen + Oxygen Yields Water 4 hydrogen atoms 4 hydrogen atoms 2H2 + O2 →2H 2O 2 oxygen atoms 2 oxygen atoms Counting Atoms How many atoms/ions are present? 3 Ba3 (PO4 )2 Ba= 9 P= 6 O=24 4(NH4 )2 SO4 N= 8 H=3 2 S= 4 O=16 Steps in Writing an Equation 1. Write the chemical symbols and or formulas for the reactants and products. 2. Check for diatomic elements. 3. Balance the equation using coefficients. Make sure atoms are equal on both sides. aluminum + oxygen yields aluminum oxide 4Al + 3 O2 → 2Al 2O3 4 atoms of aluminum + 3 diatomic molecules of oxygen yeilds 2 unit cells of aluminum oxide. #1 reason why students get an equation wrong: diatomic elements H N O F When found as elements (not in compounds), always use Cl a subscript 2 to show these that these elements are always Br found in pairs. I Diatomic molecules single covalent bond H H H H H H double covalent bond O O O O O O triple covalent bond N N N N N N Diatomic Elements in Equations. What is wrong with these equations? 2Na + 2✗Cl → 2NaCl 2Na + Cl2 → 2NaCl ✗4N + ✗2O → 2N2 O 2N2 + O2 → 2N2 O Al + ✗3F → AlF3 2Al + 3F2 → 2AlF3 Reducing Coefficients You must simplify coefficients when there is a coefficient in front of EVERY reactant & product and they are ALL divisible by the same number. Can these coefficients be reduced? ✗4K + 2F2 → 4KF 2K + F2 → 2KF ✓2Ba + O2 → 2BaO ✗4Fe2 O3 → 8Fe + 6O2 2Fe2 O3 → 4Fe + 3O2 Equations Review A chemical equation is a shorthand way of writing a chemical reaction using chemical symbols and formulas. SHS Coefficients are used in front of reactants and products to balance the equation to show that matter is conserved. .
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