7 The key to chemical reactions! The Law of Conservation of MassIn a chemical reaction, no atoms are created or destroyed. The atoms in the reacting molecules simply re-arrange to form new molecules.Since atoms aren’t created or destroyed, no mass is created or destroyed either.Mass is “conserved.”
9 In the reaction 2NaCl 2Na + Cl2 In the reaction N2 + 3H2 2NH3If 14 grams of N2 reacted with 3 grams of H2, how many grams of ammonia would be produced?In the reaction 2NaCl 2Na + Cl2If 58.5 grams of NaCl is decomposed, and 23 grams of Na is formed, how many grams of Cl2 must also be formed?
10 What else is conserved?In N H2 2NH3 besides mass (grams), what else is being conserved?Atoms?Molecules?Moles?
11 CoefficientsIn a chemical reaction, if more than 1 molecule of a substance reacts or is produced, the number of molecules is shown with a coefficient.6CO H2O C6H12O O2Coefficients multiply subscripts through the whole molecule that follows, so 6CO2 shows that there are 6 Carbon atoms and 12 Oxygen atoms.
12 How many?How many of each atom are shown by4Al2(SO4)33(NH4)3PO4
13 TerminologyIn a chemical reaction, the materials to the left of the arrow are the reactants. Reactants are consumed in the reaction.The arrow is like an equal sign in math. It can be read “react to produce” or “produces” or “forms”.The materials to the right of the arrow are the products. They form as the reaction proceeds.H2O + SO H2SO4
14 Phase NotationA chemical equation can also show the physical state of the materials in the reaction. This is done with phase notations:(s) solid (l) liquid (g) gas(aq) aqueous or dissolved in water(ppt) or ( ) means “a precipitate forms”( ) means “a gas bubbles off”means “is heated”Phase notations are written to the lower right of each formula. Clues to phase notations are often given in equations written in words.
15 An exampleWhen pellets of sodium hydroxide are dropped into an aqueous solution of iron(III) chloride, iron(III) hydroxide precipitates and sodium chloride stays dissolved.3NaOH(s) + FeCl3(aq) Fe(OH)3 (ppt) + 3NaCl(aq)