Do Now for Wednesday, January 8 th !. Think! Think! Think!!!! Explain how a simple chemical reaction might save lives. Another Chemical Reaction Saves Lives !. Without Airbag With Airbag. The Chemistry Behind Airbags. Chemical Reactions Are Used to Generate the Gas Inside an Airbag.
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5 Ways to know that a chemical reaction has occurred:1. Color Change2. Heat Produced-Gets Warm (exothermic)3. Heat Absorbed-Gets Cold (endothermic)4. Gas Produced (fizzzzz)5. Solid Produced (precipitate)These are indications of CHEMICAL CHANGES
Physical Changes do not tell you a chemical reaction has occurred!Physical change = phase changes from solidliquidgasChanges in shape
In the last unit you learned how to name compounds and write their formulas. You learned some formula “words” like:
Carbon Monoxide Carbon Dioxide Water Hydrogen Peroxide
CO CO2 H2O H2O2
Chemical Equations are the “sentences” in the language of chemistry. Chemistry students put the “words” (formulas) together to make “sentences” (chemical equations)Every chemical equation has formulas as well as special symbols.
Basic rules for chemical equations1. Chemical equations read from left to right.2. Each equation has two halves divided by an arrow. The half left of the arrow is the REACTANT side and the half rightof the arrow is the PRODUCT side.
We use COEFFICIENTS to balance an equation. Coefficients are numbers placed in front of a chemical formula in an equation and tell you how many atoms or molecules of each reactant and product are involved in the reaction.
RULES OF CHEMICAL EQUATIONS:1. The Law of Conservation of Mass states that chemical equations must start and end with the same number of atoms of each substance on both sides of the arrow. We call this a BALANCEDchemical equation!
All chemical reactions must be balanced. This means that the number of atoms on the reactant side must be equal to the number of atoms on the product side.
2. To balance the equation, you can ONLY change the coefficients, NOT the subscripts!(e.g., changing CO2to 3CO2is OK. Changing CO2to CO4is not.)
3. To calculate the number of atoms for each atom, you MULTIPLY the coefficient times the subscripts (e.g., 3 CO2= 3 Carbons and 6 Oxygens)
2H2 + O2 2H2O
Synthesis of Water
2H2O2 2H2O + O2
Decomposition of Hydrogen Peroxide
2Cu2O + C 4 Cu + CO2
Replacement of Oxygen in Copper Oxide