Chemical Formulas and Equations

Physical or Chemical Changes: Matter can undergo two kinds of changes Physical changes in a substance only affect physical properties such as size, shape or whether a solid, liquid or a gas Chemical changes Produce new substances that have properties different form those of the original substances

Chemical Changes The rust on a bike’s handlebars, for example, has properties different from those of the metal around it. A process that produces chemical change is a Chemical Reaction. Folding a newspaper in half- C or P Lighting a fire- C or P

Chemical Equations: To describe a chemical reaction you must know which substances react and which are produced The substances that react are called REACTANTS The substances that are produced are called PRODUCTS Baking Soda + Vinegar= Chemical or Physical

Chemical Rxn cont…. The bubbles that form produces a gas and something else. What goes on in a chemical rxn is more than what you can see with your eyes. Chemists are interested in which reactants are used and the products that are produced. To do this, a shorthand way of indicating what happens is called a chemical equation. C12H22O11 H2O CO2

Chemical Equations The Law of Conservation of Matter: states that nothing is created or destroyed. Therefore, the mass of the chemical reactants must be the same mass as the products Ex: Nacl -------- NaCl2 is are the elements =? When you write the chemical equation you must observe the law of conservation of matter, sometimes this easy Count the # of atoms of each type in the reactants and the products

Balancing Chemical Equations Ag + H2S -------- Ag2 S + H2 = 2 Ag + H2S ------- Ag2 + H2 Any Questions? What do you think? Complete the following exercise…

Energy in Chemicals Often, energy is released or absorbed during a chemical rxn. The energy for the welding torch is released when H and O combine to form water = 2H2 + O2 ---- 2H2O + energy. This energy comes from chemical bonds that break to form when atoms gain, lose or share electrons in the reactants and new bonds form in the product

Energy in chemical rxn… In rxns that release energy, the products are more stable and their bonds have less energy than those of the reactants. The extra energy is released in other forms such as light, sound and heat When energy is absorbed, the reactants are more stable and their bonds have less energy than those of the products 2H2 O2 + energy--- 2H2 + O2.

Energy of Rxns… Endothermic rxns occur when there is an absorption of heat energy Ex: Heating a home, cold pack (AlNO3 +H20) Exothermic rxns occur when there is a release of heat energy Ex: Burning materials, skid marks from an accident

Activation Energy…. Before a rxn can start, molecules of the reactant must bump into each other or collide This means that there must be a strong collision that will cause the molecules to speed up The amount of energy needed to speed up a chemical rxn is called the “Activation Energy” Ex: Burning of gasoline.. That’s why signs are posted at gas stations with warnings!!

Reaction Rate The rate of Rxn tells how fast a rxn occurs. To find the rate of a rxn, you can measure either how quickly one of the reactants is disappearing or how quickly one of the products is appearing Factors that affect Reaction rate are: Temperature changes, Raising Temp, Concentration of molecules and particle size

Energy in Chemicals Factors that slow down chemical rxns: Substances that slow down rxn are called inhibitors. Inhibitors do not completely stop a rxn, they simply slow down its progression of the product. Substances that speed up a rxn are called catalyst. It is used to produce the same amount of product faster

Enzymes… Enzymes are substances that can speed a rxn or slow down a rxn. Enzymes make it possible for your body to function. All enzymes are proteins, but not all proteins are enzymes. An enzyme exists to carry out each type or rxn in your body. Other uses: they contain proteases found in meat tenderizers, and contact lens

Homework: Complete section assessment 1, pg#46 (1-6). Complete Physical/chemical Changes activity handout in 6.1 pH packet All packets are due 9/23/2010