Chapter 6, Section 1 Observing Chemical Change

Matter Chemistry Anything that has mass and takes up space How matter changes Changes in matter can be physical or chemical

Physical Properties Chemical Properties Characteristics that can be observed without changing the substance into another substance – Boiling, melting, freezing points – Color, texture, hardness, flexibility Characteristics that describe the ability to change into another substance – Flammability, rusting, tarnishing

Physical Change Chemical Change Any change that alters the form or appearance of a substance but does not make that substance into another substance. A change in matter that produces one or more substances – Reactants = the substances that undergo change in a chemical reaction – Products = the new substances formed by the reaction Table talk: What are the reactants here? The products?

Chemical changes occur when bonds break and new bonds form Burning magnesium ribbon After: Magnesium oxide

Evidence for Chemical Reactions Possible changes in properties: – Color change – Precipitate forms(a solid that forms from solution) – Gas forms – Texture and hardness might change

(Evidence cont’d.) Changes in energy – Chemical reactions usually absorb or give off heat – Endothermic reaction = the total making and breaking of bonds involves absorbing energy (endo – means “in”) – Exothermic reaction = a net release of energy (“ex” means “out”) link to 3:48 video on chemical reactions (See if you can find examples of UNSAFE lab techniques) end See Math: Analyzing Data, text p. 220; “Energy of a Chemical Reaction”