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Chemical Reactions

Chemical Reactions. BELLWORK. BRIEFLY WRITE ABOUT A SCIENTIFIC OBSERVATION YOU MADE RECENTLY. Chemical equations. WE USE CHEMICAL EQUATIONS TO DESCRIBE CHEMICAL REACTIONS. Burning Coal. This is a chemical reaction

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Chemical Reactions

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  1. Chemical Reactions

  2. BELLWORK • BRIEFLY WRITE ABOUT A SCIENTIFIC OBSERVATION YOU MADE RECENTLY

  3. Chemical equations • WE USE CHEMICAL EQUATIONS TO DESCRIBE CHEMICAL REACTIONS

  4. Burning Coal

  5. This is a chemical reaction • The purpose of the equation is to show what was present before the reaction (carbon and oxygen) and afterwards (carbon dioxide)

  6. The substances that undergo change are reactants (carbon and oxygen) • New substances formed as a result of that change are called products • REACTANTS PRODUCTS

  7. CARBON + OXYGEN CARBON DIOXIDE • SIMPLIFY: C+O2 CO2

  8. CHEMICAL EQUATION • A CHEMICAL EQUATION IS A REPRESENTATION OF A CHEMICAL REACTION IN WHICH THE REACTANTS AND PRODUCTS ARE EXPRESSED AS FORMULAS.

  9. CONSERVATION OF MASS • THE LAW OF THE CONSERVATION OF MASS: MASS IS NEITHER CREATED NOR DESTROYED IN A CHEMICAL REACTION • ALTHOUGH THE MASS OF THE COAL WAS REDUCED DURING THE REACTION, IT WAS NOT LOST • THE MASS OF THE CARBON DIOXIDE CREATED WAS EQUAL TO THE MASS OF THE COAL THAT WAS LOST

  10. BALANCING EQUATIONS • ACCORDING TO THE LAW OF CONSERVATION OF MASS, EACH SIDE OF AN EQUATION MUST BE EQUAL • H2 + O2 H2O • WHAT IS WRONG WITH THIS EQUATION?

  11. TO BALANCE WE SIMPLY ADD COEFFICIENTS: • THE NUMBERS THAT APPEAR BEFORE THE EQUATION H2 + O2 H2O = H2 + O2 2H2O • WHAT IS WRONG WITH THIS EQUATION? • HOW CAN WE FIX IT?

  12. ANSWER • 2H2 + O2 2H2O • WHICH MEANS: • TWO MOLECULES OF HYDROGEN REACT WITH ONE MOLECULE OF OXYGEN TO YIELD TWO MOLECULES OF WATER

  13. http://PHSchool.com/webcodes10/index.cfm?wcprefix=ccp&wcsuffix=1071&area=view&x=13&y=7http://PHSchool.com/webcodes10/index.cfm?wcprefix=ccp&wcsuffix=1071&area=view&x=13&y=7

  14. MATH SKILLS • READ OVER THE MATH SKILLS EXAMPLES AND STEPS FOR BALANCING EQUATIONS ON PAGE 195 • THEN, TRY THE MATH PRACTICE 1-3

  15. Balancing equations tutorials • http://www.youtube.com/watch?v=RnGu3xO2h74 • http://www.youtube.com/watch?v=gskm-dfKv5g

  16. BELLWORK • BALANCE THE FOLLOWING CHEMICAL EQUATION: • H2+O2 H2O

  17. WHAT ARE SOME UNITS OF MEASURE THAT YOU KNOW OF?

  18. VERY A large amount!!!! A. What is the Mole? • A counting number (like a dozen) • Avogadro’s number (NA) • 1 mol = 6.02  1023 items

  19. Counting with Moles • MOLE: (MOL) AN AMOUNT OF A SUBSTANCE THAT CONTAINS APPROXIMATELY 6.02 X 1023 PARTICLES OF THAT SUBSTANCE. • KNOWN AS AVOGADRO’S NUMBER • A MOLE OF A SUBSTANCE GENERALLY CONTAINS 6.02 X 1023 ATOMS, MOLECULES, OR IONS OF THAT SUBSTANCE

  20. A. What is the Mole? HOW LARGE IS IT??? • 1 mole of pennies would cover the Earth 1/4 mile deep! • 1 mole of hockey pucks would equal the mass of the moon! • 1 mole of basketballs would fill a bag the size of the earth!

  21. Molar Mass • THE MASS OF DIFFERENT ELEMENTS ARE DIFFERENT, AS IS THEIR MOLAR MASS • THE MOLAR MASS OF AN ELEMENT IN THE SAME AS ITS ATOMIC MASS EXPRESSED IN GRAMS

  22. MASS OF COMPOUNDS • YOU CAN FIND THE MASS OF COMPOUNDS BY ADDING THE MASS OF THEIR COMPONENTS • A CARBON DIOXIDE MOLECULE: • CARBON= 12 GRAMS • OXYGEN = 16 GRAMS X 2 = 32 GRAMS • 12 + 32 = 44 GRAMS • CARBON DIOXIDE HAS A MOLAR MASS OF 44 GRAMS

  23. LETS TRY • MOLAR MASS OF C • MOLAR MASS OF Fe • MOLAR MASS OF H2O

  24. MOLE-MASS CONVERSIONS • TO FIND HOW MANY MOLES ARE IN A CERTAIN # OF GRAMS OF AN ELEMENT OR MOLECULE: • Y GRAMS x 1/z grams= x moles

  25. Example • WE HAVE 55 GRAMS OF CO2 • HOW DO WE FIND HOW MANY MOLES WE HAVE? • 55 X 1 mol/44 g • 1 mol/44 g=.02272727 mol • .02272727mol X 55 g = 1.25 mol CO2

  26. BELLWORK WHAT IS A MOLE? WHY DO WE USE MOLES? HOW MUCH IS ONE MOLE OF BARIUM IN GRAMS? CARBON DIOXIDE? WATER?

  27. REVIEW: • A mole is just a number, nothing else • That number is 6.02 x 1023 • We use this number to make otherwise incredibly small numbers (such as the mass of an atom) easy to use in chemical formulas

  28. Review • There are two conversions we will do with moles: • Find how many moles there are in a certain number of grams (mass) an element or molecule • Find the the number of grams (mass) there are in a certain number of moles of an element or molecule

  29. Two conversion factors a) Grams b) 1 Mol 1 Mol or Grams How many grams, use conversion factor a How many moles, use conversion factor b

  30. Practice • Suppose we have 55 grams of CO2 • How do we find how many moles of CO2 there are in 55 grams of CO2? • Step 1: find the molar mass of CO2 44 grams/mole • Step 2: set up the equation 55 grams CO2 x 1 mol CO2 = ? mol CO2 44 grams CO2

  31. Step 3: Solve the equation 55 grams CO2 x 1 mol CO2 = ? molCO2 44 grams CO2 1/44= .0227 55 x .0227 = 1.25 There are 1.25 moles of CO2 in 55 grams of CO2

  32. Flip it! • Now, suppose we have 2.4 moles of sulfur. • How do we find how many grams there are in 2.4 moles of sulfur? • Step 1: Find the molar mass of sulfur. 32.07 grams/mole • Step 2: Set up the equation: 2.4 moles x 32.07 grams S = ? Grams S 1 mol S

  33. Step 3: solve the equation: 2.4 x 32.07 = 77 grams sulfer There are 77 grams of sulfur in 2.4 moles of sulfur

  34. Get into the groups I assigned the other day. • Work on the worksheet together. • Do as many problems as you can.

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