Think about it:1. Whats the difference between cutting and burning a piece of wood?
2. How should the mass of the products (results of each process) compare to the original piece of wood?
And how to tell the difference
Physical and Chemical ChangesAGENDA:Distinguishing and identifying changes
Steel wool demonstration (this will get started early in the lesson, but we will revisit it several times.
Guided practice to distinguish changes.
Physical ChangeSubstance may seem different, but the way the atoms combine is the same.Chemical ChangeChanges the way the atoms combine to form substances(new substances will have different physical properties)
Steel Wool Demonstration We will be taking observations every 5 minutes for this demonstrations
Its a physical change ifIt changes shape or sizeIt dissolves.It changes phase (freezes, boils, evaporates, condenses)
Its a chemical change ifIt burnsTemperature changes without heating/coolingIt bubbles (makes a gas)It changes colorIt forms any new materialsHow are these different?
What kind of change is it if someone...Tears up paper?Physical changeMixes salt and water?Physical change
What kind of change is it if someone...Burns paper?Chemical changeEvaporates salt water?Physical change
What kind of change is it if someone...Mixing vinegar and baking soda?
Guided Practice (Left Side):For each of the following examplesDecide whether the changes is chemical or physicalJustify your answer.
Boiling water is a physical change because the liquid water changes state to become water vapor when enough heat is added.
Physical or Chemical Change?Painting WoodPHYSICAL
Physical or Chemical Change?Burning PaperCHEMICAL
Physical or Chemical Change?Digestion of foodCHEMICAL
Physical or Chemical Change?Sugar dissolving in waterPHYSICAL
Physical or Chemical Change?A pond freezing in winterPHYSICAL
Physical or Chemical Change?Cutting wirePHYSICAL
Law of Conservation of MassMatter can never be created or destroyed.This means:During any physical or chemical change, the total mass of all substances before and after the change remains the same.Sometimes, measuring all the components of a change is difficult.Example: if you boiled water, it would be difficult to measure the mass of all the water vapor.
Temperatures influence on chemical changesThis means:During any physical or chemical change, the total mass of all substances before and after the change remains the same.
Time (min) Mass (g)ColorOther ObservationsRoomtemp.HotRoomtemp.HotRoom temp.Hot0
Teachers: assign a time keeper for the demonstrations and have students assist with recording observations*Students should distinguish boiling (phase change) from creating of a new gas. Boiling water and the bubbles (carbon dioxide) released from mixing vinegar and baking soda can be used as a reference for students.
*The following examples can be used as think-alouds to model how students should justify answer. Use of individual or group whiteboards or another type of response system can be used to check for understanding.*
*This is the only slide from the guided practice that has a modeled justification. All other examples only state whether to the processes is a physical or chemical change.*