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10 th Grade Chemistry: 2/23/14

Learning Target: Construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties. 10 th Grade Chemistry: 2/23/14.

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10 th Grade Chemistry: 2/23/14

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  1. Learning Target: Construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties. 10th Grade Chemistry: 2/23/14 Must Do: Make a list of all the combustion reactions that you might encounter on a regular basis. Shoot for three and write down what the application is (e.g., BBQ). • Agenda: • Must Do • WWK • Brief Lesson/video

  2. WWK

  3. Combustion • 1:  an act or instance of burning • 2:  a usually rapid chemical process (as oxidation) that produces heat and usually light; also:  a slower oxidation (as in the body)

  4. Goal for this unit • Write a complete and balanced chemical equation from a prompt • This time, let’s change it up a little…. • From the short demonstration, what is the reaction taking place when sparks lands on a piece of steel wool (steel wool is 99% iron)? • Or we grind a piece of iron with grinding wheel?

  5. Reaction (generally…there are always some iron oxides present) • Fe (s) + O2 (g) Fe2O3 (s) • This reaction produces a red-hot glow in the steel wool that will eventually convert all the solid iron to iron (III) oxide • The formula for iron (III) oxide is Fe2O3 because we need to balance the charges between the Fe3+ (iron (III)) and O2- (oxide ion). • To equalize the charges and make the compound nuetral, we criss-cross the charges as shown in the arrows below. Two Fe(III) give 6+ charge and three O2- give us 6-. Thus, the charges are equal. Fe3+O2- Fe2O3

  6. Now…what if we were to mix in some Aluminum? • Fe2O3 (s) + Al (s) Fe(s) + Al2O3 (s) • Recall that the reaction took a while to initiate. The iron had to first convert to Fe2O3, once this occurred, the addition of aluminum, plus some heat, initiated the reaction above. • The overall reaction was a Combustion (synthesis) followed by a single replacement reaction.

  7. Combustion Reactions • Combustion reactions always involve molecular oxygen O2. Anytime anything burns (in the usual sense), it is a combustion reaction. Combustion reactions are exothermic (i.e., they give off heat). For example when wood burns, it must do so in the presence of O2 and a lot of heat is produced.

  8. Ideal Combustion Reaction • Hydrocarbon + O2 CO2 + H2O • Where have we seen this? • Aerobic respiration • Aerobic respiration may be represented by the general equation C6H12O6 + 6O2  6CO2 + 6H2O • About 3000 kJ mol-1 of energy is released. Burning glucose in air would release this amount of energy in one go. However, it is not as simple as this in aerobic respiration. Aerobic respiration is a series of enzyme-controlled reactions that release the energy stored up in carbohydrates and lipids during photosynthesis and make it available to living organisms.

  9. Un-Controlled Oxidation of Glucose

  10. Combustion Continued • The general form for combustion is really just for burning some chemical (or elemental) compound in oxygen. • In the real world, combustion is much more complicated • Burning hydrocarbons in air (78% N2) gives products like NO, NO2, N2O, etc. • Incomplete combustion (in an environment where there is not enough O2), yields CO, un-burned fuel and “soot” http://chemwiki.ucdavis.edu/Physical_Chemistry/Kinetics/Case_Studies/Catalytic_Converters

  11. Catalytic Converter

  12. Balancing Equations…. • From my observations of the formative quiz…. • We need to get the nomenclature fixed. • Subscripts are for the number of atoms in a compound • Superscripts are for charges • Coefficients are for the number of atom or molecular units in the reactanst or products

  13. Start Working on Balancing Chemical Equations • The class time today moved into balancing reactions before I wanted! The practice sheets were intended to give you some exercises to work on for Wednesday. • Wednesday’s class, we will back up a bit and start working on equations that already have the chemical formulas written, so we only work on one skill at a time…..

  14. Elements that Exist (primarily) as Diatomic molecules (need to know this to write a correct chemical formula) • One way to remember the seven diatomic elements is to start at element 7 (nitrogen) on the periodic table, and trace a "7" (move right to fluorine and then down to iodine). Counting the elements in the “7” shape, you will find six elements. The seventh is hydrogen—it is way up in the top left-hand corner of the periodic table. • Another way to remember the diatomic elements is that they all end in either -ine (fluorine, chlorine, bromine, iodine) or -gen (hydrogen, nitrogen, oxygen). For the polyatomic elements, you may find it helpful to remember that phosphorus and sulfur are found beneath the top part of the “7” shape.

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