Ch. 11 Chemical Equations Chemical reaction - One or more reactants change into one or more products (atoms rearrange their attachments = new substances) Chemical evidence - (Ch. 2) Bubbles, precipitate, change of temp, change in color Reactants - A substance present at the start of a reaction Products - A substance generated in a chemical reaction Evidence of a Chemical Change Chemical Change the particles in a compound break apart from their current chemical attachments (bonds) and rearrange to form new attachments. Either to new and different elements or in new amounts of attachments. Bubbles - (baking soda in vinegar, or bubbles in electrolysis) Change in temperature - (heat given off in a burning reaction) Formation of a precipitate - (our lab example) Sometimes changes in appearance - color, sound, texture, rot KC 7 = Write the names of the reactants to the left of a yields arrow separated by + signs; then write the names of the products to the right of the arrow also separated by + signs What is cumbersome (difficult) about a word equation? So many words to express what can ver y simple thing when using symbols and formulas (like a shorthand) Chemical equation = A representation of a chemical reaction Not to be confused with a Chemical Reaction KC 8 Skeleton equation = write the reactant and product formulas A chemical equation that doesnt indicate the relative amounts of the reactants and products (no numbers in front) Descriptor (Equation Symbol) Similar to adjectives in English, they are extra symbols to enhance the detail in describing a chemical equation Coefficient - Small whole numbers that are placed in front of formulas in an equation in order to balance it Balanced equation - Each side of the equation has the same number of atoms of each element and mass is conserved Bonds are rearranged Chemical Reactivity 2H 2 (g) + O 2 (g) 2H 2 O(g) Law of Conservation of Mass = the masses have to add up, nothing is created or destroyed, what goes in must come out KC 22Combination (or Synthesis) Decomposition Single replacement Double replacement Combustion