Chemical Reactions Chapter 4.1–4.2 & Ch 5.1–5.3

Chemical Reactions Chemical Reaction: A process that transforms one set of chemical substances into another When atoms break existing chemical bonds and form new ones Evidence of a chemical reaction: Change in properties (new substance, color) Change in energy (temperature or light)

Chemical Reactions Reactants are the chemicals present BEFORE the reaction Products are the chemicals present AFTER the reaction

Chemical Equations Ex: CaCO3  CaO + CO2 Chemical Equations symbolize what happens during a reaction like a math equation…with  instead of = REACTANTS  PRODUCTS Reactants and products are shown as chemical formulas Ex: CaCO3  CaO + CO2 When limestone is heated, it changes into calcium oxide and carbon dioxide Notice that the elements are the same before and after the reaction. heat

CaCO3  CaO + CO2 Mass is Conserved The same atoms that are present at the start of the reaction (reactants) are also there at the end (products). CaCO3  CaO + CO2 1 calcium, 1 carbon, and 3 oxygen atoms The atoms are simply rearranged

Mass is Conserved Law of Conservation of Mass: The mass of the products will equal the mass of the reactants Matter is neither created nor destroyed. The atoms present in the reactants are the same atoms that form the products…they are just rearranged.

Controlling Reactions Chemists can control the rate of a reaction by adjusting the temperature. Increasing the temperature will speed up the reaction Molecules are moving faster so they collide more frequently Decreasing the temperature will slow down the reaction Molecules are moving slower so they collide less frequently

Controlling Reactions Chemists can also control the rate of a reaction by adjusting the: Concentration –amount of a substance in the reaction Higher concentration  bigger/faster reaction Surface Area – amount of surface exposed to the reaction Greater surface area  faster reaction Catalysts and Inhibitors – chemicals that speed up or slow down the reaction Catalysts – speed up the reaction or cause it to happen Inhibitors – slow down the reaction or cause it to stop