Counting Atoms & Recognizing Balanced Equations

Counting Atoms in a chemical formula A chemical formula is a description of the number and kind of atoms found in a single molecule of a substance, using the symbol for each element and a subscript number to state the number of atoms of the element to the left of the symbol. When a chemical formula has a coefficient you multiply the coeffiecient by all the atoms of each element on the molecule. 2 4 1 2 1 1 3 1 8 2 3 2 2 4 2 3 6 3 12 4 4 24 8 Introduction to Balancing Chemical Equations Use this video if you need help in answering the next question. B U B B U U Identify the reactants and products in the following chemical equations:1) HCl + NaOH → H2O + NaCl2) KNO3 → KNO2 + O23) 2NH4OH+CuSO4 → (NH4)2SO4 + Cu(OH)2 Reactants HCl NaOH KNO3 2NH4OH CuSO4 Products H2O NaCl KNO2 O2 (NH4)2SO4 Cu(OH)2 Count the Atoms Count the number and types of atoms in the reactants and products 2NH4OH + CuSO4 → (NH4)2SO4 + Cu(OH)3 Element Name Number of atoms in the reactants Number of atoms in the products Nitrogen (N): 2 2 Hydrogen (H): 10 11 Oxygen (O): 6 7 Copper (Cu): 1 1 Sulfur (S): 1 1 Signs of a Chemical Reaction Match the sign with the appropriate example. A blue solid formed with ammonia (liquid) mixed with copper sulfate (liquid). Precipitate A balloon inflated after hydrogen peroxide broke down into water and oxygen. Gas released Copper sulfate and iron where both at room temperature before they were mixed. After, the container became very hot. Unexpected temperature change Your black jeans turned a reddish color after you spilled bleach on them. Unexpected color change. Decide whether or not the example is a physical change or a chemical change. Physical Change An egg shell was cracked open A cookie was broken in half Lemonade powder was dissolved Vinegar evaporated Chemical Change Plants produce sugar and oxygen from carbon dioxide and water during photosynthesis. Eggs were cooked Cookie dough was baked An iron key rusted Looking at the video of the flask on the balance, how do you know a chemical reaction has occurred? Why does the mass stay the same?