Physical v. Chemical

Physical Properties vs Chemical Properties Physical Properties – can be observed without changing the identity of the substance Examples: odor, color, taste, volume, state, hardness, density, melting and boiling points

Physical Properties vs Chemical Properties Chemical Properties – its ability to form new substances Examples: flammability, oxidation/corrosion

What is oxidation?? Oxidation is the interaction between oxygen molecules and all the different substances they may contact, from metal to living tissue.  Freshly cut apple turning brown Bicycle fender rusting Penny suddenly turning green https://www.youtube.com/watch?v=p3P0mjeb5UU *Prevent oxidation? Need a layer of protection

Physical or Chemical Properties? Boiling Point of an alcohol Diamonds are hard Sugars ferments to form alcohol A metal wire conducts an electric current Metal wire still a metal wire before and after the current passes thru it

Physical Changes *Usually reversible (not always) Physical Change – a change that does not affect the composition of a substance Change like: Crushing, ripping, breaking or any phase change Most common physical (phase) changes: solid  liquid  gas So our lab yesterday had physical and chemical changes. We are going to define them today. So what that means is there is no change in the main part that makes up the substance. Change in (the physical properties): odor, ect, but the main composition of the substance stays the same. When something changes physical states and nothing else is added to it, then we have a physical change. By the way, states of matter can be classified as solid, liquid or gas. Anyway, water can be a solid as in ice, or a liquid as in water, or a gas as in water vapor. The water still has the same molecules associated with each one and does not have other substances, so it is a physical change. The molecules stay INTACT *Chemical bonds are not broken

Physical Changes: Names of the Phase Changes Solid Gas Liquid SolidAqueous = ___________ Aqueous  Solid = ___________ dissolving crystallizing

Chemical Changes *Irreversible Chemical Change – a change that a substance becomes a new, different substance. Chemical changes are called reactions. Changes like: Burning, rusting, rotting or decomposing, fermenting, cooking, baking and other chemical reactions *Chemical bonds are broken and molecules rearrange to form new bonds Changes in the chemical properties which is the ability to form a new substance. A physical change does not make a new substance, while a chemical change does. So one way, you can tell the difference between chemical and phyiscal changes is: if you can change it back (ice  water) or does it still look the same (a ripped piece of paper)? That is a physical change. Most chemical changes are irrversible, some are like recharging batteries.

Indications of a Chemical Reaction/Changes Temperature Changes Gives off heat (exothermic), absorbs heat (endothermic) Produces a gas Changes color a new color is formed Odor changes Produces a solid (precipitate) How can we tell if a chemical reaction took place. Matter is neither created nor destroyed in a chemical reaction. https://www.youtube.com/watch?v=M8tyjwB42X4

Physical or Chemical Changes? Ice melting to water Burning Paper Baking a cake Putting blue food color in water

2. Salt dissolving in water Exit Slip Label as physical or chemical change: 1. Making ice cubes 2. Salt dissolving in water