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. - PowerPoint PPT Presentation
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. 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). 10 th Grade Chemistry: 2/23/14 Agenda: •Must Do •WWK •Brief Lesson/video
Transcript
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.
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).
10th Grade Chemistry: 2/23/14
Agenda:•Must Do•WWK•Brief Lesson/video
WWK
Combustion1: 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)
Goal for this unitWrite 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?
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
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.
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.
Ideal Combustion ReactionHydrocarbon + O2 CO2 + H2O
Where have we seen this?
Aerobic respirationAerobic respiration may be represented by the
general equation
C6H12O6 + 6O2 6CO2 + 6H2OAbout 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.
Un-Controlled Oxidation of Glucose
Combustion ContinuedThe general form for combustion is really just for
burning some chemical (or elemental) compound in oxygen.
In the real world, combustion is much more complicatedBurning 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”
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
compoundSuperscripts are for chargesCoefficients are for the number of atom or
molecular units in the reactanst or products
Start Working on Balancing Chemical
EquationsThe 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…..
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.
