Chapter 2 Section 3: Changes in Matter Key Concepts: Chemical change Law of conservation of mass What is a physical change? What is a chemical change? Energy Temperature How are changes in matter related to changes in energy? Thermal energy Endothermic change Key Terms: Physical change Exothermic change

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Physical Change A physical change is any change that alters the form or appearance of matter but does not make any substance in the matter into a different substance. (remember physical properties ?) A substance that undergoes a physical change is still the same substance after that change. Changes of state (liquid, gas, or solid) Changes in shape or form (example: crushing a can doesn’t change the composition of the can)

Chemical Change A chemical change is a change in matter that produces one or more new substances. Produces new substances with properties different from the original substances Examples: (remember cheeeemmical prrrroperties?) Combustion – produces heat, light, and a new substance Electrolysis – use of electricity Oxidation – combination of oxygen and substance Tarnishing – bright metal becomes dark coating on metal

Law of conservation of mass Law of conservation of mass: Matter is not created or destroyed in any chemical or physical change. No mass is ever lost because atoms are rearranged, NOT LOST. 

Matter and thermal energy Energy is the ability to do work to cause change. Every chemical or physical change in matter includes a change in energy – sometimes it is USED, and sometimes it is RELEASED.

Temperature and thermal energy Temperature is a measure of the average energy of random motion of particles of matter Thermal energy is the total energy of all the particles in an object Question: What has more thermal energy? The ocean or a cup of water? (How do you learn how to answer a question like this?)

Well.. If thermal energy is the total energy of all of the particles, then it would depend on what has more particles. More particles = more total energy. So the ocean has more. For temperature, it is the AVERAGE energy. So the temperature of the water cup and the ocean could be the same. Questions on this?

Thermal Energy changes  Thermal energy and changes in matter Endothermic change – energy taken in Exothermic change – energy released

Forms of energy May include kinetic, potential, chemical, electromagnetic, electrical, and thermal

Review questions: What is the difference between a chemical change and a physical change? What is thermal energy? True or false: during a change, energy is always released.