Coach Dave Edinger J. C. Booth Middle School Physical Science (8A)

Changes in Matter Chemistry is the study of the properties of matter and the ways in which matter changes. Chemistry is the study of the properties of matter and the ways in which matter changes.

Changes in Matter (cont … ) A change that alters the form or appearance of a substance, but does not change the material into a new substance is called a physical change. A change that alters the form or appearance of a substance, but does not change the material into a new substance is called a physical change. A change in matter that produces new substances with new and different properties is called a chemical change. A change in matter that produces new substances with new and different properties is called a chemical change.

Changes in Matter (cont … ) The key characteristic of a chemical reaction is the production of new materials that are chemically different from the starting materials. The key characteristic of a chemical reaction is the production of new materials that are chemically different from the starting materials.

A solid that forms from the combination of 2 liquids is called a “ precipitate. ” It always indicates a chemical reaction has occurred.

A color change almost always indicates a chemical reaction ….

Any time something is burned, a chemical reaction is occurring …

Gas production (in the absence of a heat source) is a key indicator that a chemical reaction is taking place.

New and different properties are the mark of a chemical change …

Can you tell the difference between a chemical and physical change???

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++ = 7

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+ = 10

Describing Chemical Reactions A chemical equation is a quick and easy way to display a chemical reaction using symbols. A chemical equation is a quick and easy way to display a chemical reaction using symbols. H + O 2  H 2 O H 2 + O 2  H 2 O

Describing Chemical Reactions H + O 2  H 2 O H 2 + O 2  H 2 O Reactants- Materials present at the beginning of the reaction Products- New materials formed from the completion of the reaction Reactants Product(s)

Describing Chemical Reactions The law of Conservation of Mass states that the total amount of matter in a chemical reaction does not change! The law of Conservation of Mass states that the total amount of matter in a chemical reaction does not change! ?????

Balancing Chemical Equations H + O 2  H 2 O H 2 + O 2  H 2 O H= 2 atomsH= 2 atoms H= 2 atomsH= 2 atoms O= 2 atomsO= 1 atom O= 2 atomsO= 1 atom THIS VIOLATES THE LAW OF CONSERVATION OF MASS!!! THIS VIOLATES THE LAW OF CONSERVATION OF MASS!!!

Balancing Chemical Equations __ H + __O 2  __H 2 O __ H 2 + __O 2  __H 2 O A Coefficient is the number in front of a chemical formula that tells you how many molecules of each reactant and product are present. 22 H= 4 0= 2 H= 4 0= 2 BALANCED!!

Characterizing Chemical Reactions A synthesis reaction occurs when smaller molecules combine to form larger ones (more reactants than products) A synthesis reaction occurs when smaller molecules combine to form larger ones (more reactants than products) 12H 2 O + 12CO 2 + light  2C 6 H 12 O O 2

Characterizing Chemical Reactions Decomposition reactions occur when chemicals break down into smaller molecules (more products than reactants). Decomposition reactions occur when chemicals break down into smaller molecules (more products than reactants). 2H 2 O  2H 2 + O 2

Characterizing Chemical Reactions A replacement reaction occurs when portions of molecules switch places with one another (the number of products is the same as the number of reactants) A replacement reaction occurs when portions of molecules switch places with one another (the number of products is the same as the number of reactants) CaCl 2 + Na 2 SO 4  CaSO 4 + 2NaCl Precipitate

Energy in Chemical Reactions Every chemical reaction involves a change in energy … some reactions release energy and some absorb energy. Every chemical reaction involves a change in energy … some reactions release energy and some absorb energy.

Energy in Chemical Reactions A reaction that releases energy in the form of heat is called an exothermic reaction. A reaction that releases energy in the form of heat is called an exothermic reaction. 2Na + 2H 2 O  2NaOH + H 2

Energy in Chemical Reactions A kind of reaction that absorbs energy is called an endothermic reaction. A kind of reaction that absorbs energy is called an endothermic reaction.

Getting Reactions Started There is always a minimum amount of energy needed to start a chemical reaction … this is referred to as the “ activation energy. ” There is always a minimum amount of energy needed to start a chemical reaction … this is referred to as the “ activation energy. ”

Rates of Chemical Reactions Rates of chemical reactions are affected by ….

Rates of Chemical Reactions Concentration Concentration

Rates of Chemical Reactions Surface area Surface area + =

Rates of Chemical Reactions temperature temperature

Rates of Chemical Reactions Catalyst- (a material that increases the rate of a chemical reaction by lowering the activation energy) Catalyst- (a material that increases the rate of a chemical reaction by lowering the activation energy)

Rates of Chemical Reactions A catalyst is a substance that increases the rate of a chemical reaction without being consumed. A catalyst is a substance that increases the rate of a chemical reaction without being consumed.

“That’s All Folks!” More to come…