CHEMICAL REACTIONS

Chemical Equations Reactants – substances that undergo changes Products – new substances formed from reaction Reactants Products N2 + 3H2 2NH3

Conservation of Mass *Mass is not created in chem. reaction *Mass in not destroyed in chem. Reaction

Types of Reactions Synthesis Decomposition Single-replacement Double-replacement Combustion

Synthesis Two or more substances react to form a single substance A + B AB Example: 2H2 + O2 H2O

Decomposition A compound breaks down into two or more simpler substances Reactant MUST be a compound! Products may be elements or compounds AB A + B 2H2O 2H2 + O2

Single Replacement One element takes the place of another element in a reaction A + BC B + AC Cu + 2AgNO3 2Ag + Cu(NO3)2

Double Replacement Two different compounds exchange positive ions to form two new compounds AB + CD AD + CB CaCO3 + 2HCl CaCl2 + H2CO3

Combustion Substance reacts with oxygen Often creates heat and light CH4 + 2O2 CO2 + 2H20

Internal Combustion Engine

Reaction Rates Reaction Rate – rate at which reactants change into products over time. TNT vs. Leaves changing

Reaction Rates ~ 200 – 350 calories -A Cal X-Country runner burns calories- energy is released OR -Just burn the bar! -energy released faster! **Same amount**

Factors affecting reaction rates… An increase in TEMPERATURE increases reaction rate. Decrease in temp = decrease in reaction rate.

Surface area Increase in surface area of a reactant increases reaction rate.(and vice versa)

Stirring Stirring reactants increases reaction rate.

Concentration The more reacting particles, the more likely a reaction will occurr. Concentrated detergent Grape juice concentrate

Catalysts Catalyst – substance that affects reaction rate without being used up. Making friends…

Equilibrium When opposing changes take place at the same rate. Physical and Chemical equilibria. Reversible Reaction: A + B C

Reactions… Exothermic – releases energy to its surroundings. Warm test tube??? Endothermic – absorbs energy from surroundings.

MOLES Mole – amount of a substance that contains ~ 6.02 x 1023 particles of that substance Avagadro’s number (don’t worry about it.) Marbles?

Mole vs. Dozen Eggs vs. Donuts A dozen eggs has a different mass than a dozen donuts. *But its still a dozen! **A mole works the same as a dozen**

Molar Mass *The mass of one mole of a substance = molar mass *Molar Mass = same as Atomic Mass but expressed in Grams! ??? What’s the molar mass of Carbon??? ???Sulfur???

Mole - Mass Conversions CO2 = ~ 44 grams C = ~ 12 grams O2 = ~ 32 grams Conversion Factor: 44.0g CO2 OR 1 mol CO2 1 mol CO2 44.0g CO2

Mole Conversions… Say you have… 50g of CO2 How many moles of CO2 do you have??? Use conversion factor: 50g CO2 X 1 mol CO2 = 50.0g CO2 44.0g CO2 44.0g CO2 ANSWER = 1.14 moles of CO2

Converting… Convert 1.25 mol MgCl2 to grams! 1. Find out 1 mole of MgCl2 by adding atomic mass of each element. Mg = ~24 + Cl = ~35 + Cl = ~35 = 94 2. Use correct conversion factor: 1.25 mol MgCl2 X 94g MgCl2 1mol MgCl2 3. Multiply across and cancel like units! ANSWER = ~ 118g MgCl2