Physical and Chemical Changes 8th Grade Physical Science Betsy Sanford

Physical Property Observed traits, qualities, attributes Help describe/identify a substance Can be seen or measured without changing a substance Examples: color, shape, smell, taste Measurements - mass, volume, density state (solid, liquid, gas) temperature for change of state – melting point, freezing point, boiling point

Physical Property More examples: ductility (ability to be made into wires) malleability (ability to be shaped without breaking) conductivity (ability to carry electric current or heat) solubility (ability to dissolve)

Physical Change Any change in size, shape, form, or state where the identity of the matter stays the same Example: cutting a watermelon into slices tearing a sheet of paper sharpening a pencil Often easy to reverse with: filtration, magnetism, evaporation, distillation and centrifuge (spinning)

Physical Change More examples: boiling freezing melting condensing evaporating stretching into wire hammer into sheet Dissolving sugar in tea transferring heat or electricity

Physical Change Evidence for a physical change: same substance before and after no new substances a color change a state change (solid, liquid, gas) same smell, taste, texture different volume different density

Chemical Property Traits that allow a substance to change Testing for chemical properties causes a change in the substance Examples: flammability (ability to catch fire) combustibility (ability to explode) reactivity with oxygen reactivity with water acidity (pH, reaction with hydrogen)

Chemical Change chemical change happens when a substance undergoes a change that causes its traits to change new materials are formed that are different from the starting materials Examples: digestion (breakdown of food) photosynthesis (plants making food) burning fuel exploding fireworks rusting formation of different gas

Chemical Change NOT easily reversed Evidence for a chemical change more than one of the following occurs: release of energy (light, heat, sound – change in temperature) formation of new substance (a different gas or solid that is not just a state change) color change, odor change change in conductivity

Chemical Change Chlorine added to swimming pools and drinking water causes acidity (change in pH) prevents reproduction, growth and development of algae, bacteria, protists and insects.

Energy… …is required for both types of changes

Table of Physical and Chemical Changes Physical Changes Chemical Changes Paper cut in half Sour milk Modeling clay Tarnished jewelry Butter melting Burned toast Ice forming Rust on a nail Water evaporating Gas grilling Sweet tea Apple rotting Bowl of cereal Frying an egg Makeup on your face Lit match Crushing a can Cellular respiration

Lab Evidence - Physical vs. Chemical Change Physical Changes Chemical Changes color change substance is the same, but may be a different size or shape new substance changing state fizzing or foaming dissolving heat gain or heat loss bending, crushing production of sound, light, or odor mixing, cutting change cannot be undone