Physical & Chemical Changes Changing Matter Physical & Chemical Changes

What different ways can we differentiate between my sisters? Properties How we identify something. All substances have properties that we can use to identify them. For example we can identify a person by their face, their voice, height, finger prints, DNA etc.. The more of these properties that we can identify, the better we know the person. In a similar way matter has properties - and there are many of them. There are two basic types of properties that we can associate with matter.

Matter has properties Two basic types of properties that we can associate with matter. Physical properties Chemical properties

Physical Properties Anything that can be observed without changing the identity of the substance. (Tends to be measurable.) melting point density boiling point thermal conductivity electrical conductivity ductility color malleability

Chemical Properties The way a substance may change or react to form other substances heat of combustion Reactivity to other chemicals reactivity with water PH Oxidation Flammability Chemical properties of matter describes its "potential" to undergo some chemical change or reaction by virtue of its composition. What elements, electrons, and bonding are present to give the potential for chemical change. It is quite difficult to define a chemical property without using the word "change". Eventually you should be able to look at the formula of a compound and state some chemical property. At this time this is very difficult to do and you are not expected to be able to do it. For example hydrogen has the potential to ignite and explode given the right conditions. This is a chemical property. Metals in general have they chemical property of reacting with an acid. Zinc reacts with hydrochloric acid to produce hydrogen gas. This is a chemical property.

Matter can be changed two ways Physically Physical reaction Physical change Chemically Chemical reaction Chemical change

Physical Changes Do NOT CHANGE THE TYPE OF MATTER Nothing new or different is formed Could be a change in: Mass Volume Density Change in state Color Shape Size

Examples of Physical Changes Boiling Freezing Dissolving Breaking Making a mixture 2 or more types of matter (substances) mixed together Not in specific amounts Can be separated physically

Picture from www.chem4kids.com Chemical Changes The composition of the substance changes. The substances present at the beginning of the change are not present at the end; new substances are formed. The change cannot be “undone.” Picture from www.chem4kids.com

Chemical Changes Evidence of a chemical reaction Formation of gas Formation of precipitate Change in color Change in energy Endothermic Absorbs heat energy (gets cold) Exothermic Releases heat energy (gets hot) Alka-Seltzer: (Baking soda or sodium bicarbonate) NaHCO3 + Citric acid ---> CO2 + H2O + Sodium Citrate

Chemical Changes Atoms are re-arranged, NOT created or destroyed

Law of Conservation of Matter Matter is conserved  type of atoms does not change Nothing is created or destroyed

Law of Conservation of Mass Mass is conserved  amount of atoms cannot change Nothing is created or destroyed