Presentation on theme: "Chemical Reactions. Atoms Interact in Chemical Reactions Chemical reaction - Produces new substances by changing the arrangement of atoms."— Presentation transcript:
Atoms Interact in Chemical Reactions Chemical reaction - Produces new substances by changing the arrangement of atoms
Atoms and the Periodic Table Periodic Table shows many different things: –Symbols –Names –Other stuff too Number of protons Number of neutrons Atomic Weight 17 Cl Chlorine 35.45
Reactants and Products Reactants - the substances present at the beginning of the reaction Products - the substances formed by the chemical reaction
Evidence of Chemical Reactions Color change Formation of a precipitate Formation of gas Temperature change
Classification of Chemical Reactions Synthesis –A new compound is formed
Classification of Chemical Reactions Decomposition –A reactant is broken down to simpler products
Classification of Chemical Reactions Combustion –One reactant is oxygen and the other often contains hydrogen and carbon –The products are always carbon dioxide and water
Rates of Reaction Rates depend on several factors –Concentration –Surface Area –Temperature
Rates of Reaction Rates depend on several factors –Presence of a catalyst Substance that increases the rate of the reaction without changing Enzymes - biological catalysts
Chemical Reactions Day 2 Conservation of Mass Balancing Equations
Law of Conservation of Mass Again Matter is neither created nor destroyed –Atom in = atom out
And your very own Periodic Table To tell which things cannot be created or destroyed
Chemical Equations Chemical equations - way to describe a chemical reaction symbolically 2H 2 + O 2 2H 2 O Yield, , shows the direction of the reaction Coefficients tell the number of molecules Subscripts show the number of atoms in the molecule
Balancing Chemical Equations Number of atoms in the reactants must equal the number of atoms in the products Balance equations using coefficients
So there’s a bit more to it… Some chemical reactions have polyatomic ions – a group of two or more atoms that act as a group –Notation for polyatomics… Na(NO 2 ) 3 1 Na atom 3 N atoms 6 O atoms
So how about this one… 2 Na(NO 2 ) 3 2 Na atoms 6 N atoms 12 O atoms
NEVER EVER ***NEVER change the subscripts to balance a chemical equation*** Changing subscripts = Changing the substance
Practice Activity Balancing chemical equations with the Hardware analogy…again
Chemical Reactions Day 3 Energy Transformation Getting hot and Being cool
Chemical reactions involve energy changes Chemical reactions involve breaking and making bonds –Breaking bonds costs energy –Making bonds gives energy The energy contained in these bonds is called the bond energy
Systems and Surroundings System – red liquidSystem – ice cube Surroundings – airSurroundings – tea, glass, cherry, lemon
Exothermic Reactions Products have more bond energy than the reactants Puts the extra energy into the surroundings –Surroundings get hot Thermite reaction videoThermite reaction video – why I can’t demo this type of reaction – and you can’t either!!!
Endothermic Reactions Products have less bond energy than the reactants Takes the extra energy out of the surroundings –Surrounding loses heat DON’T SAY GET COLD!!!
Don’t try this at home! That’s why we show it done on video by other people with the proper training and equipment!!!
Question to consider – Part I Scenario: I light a propane torch, let it run for a bit upside down, then turn it off. Question: Will the tip of the torch be hot or cold?
Question to consider – Part II Is the phase change from a liquid to a gas (evaporation) an endothermic or exothermic process? Propane torch demo