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Atom Inventory & Balancing Equations. Question… What happens to the ice cream you (or I!) eat?? What happens to the gasoline you put into your car? Do.

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Presentation on theme: "Atom Inventory & Balancing Equations. Question… What happens to the ice cream you (or I!) eat?? What happens to the gasoline you put into your car? Do."— Presentation transcript:

1 Atom Inventory & Balancing Equations

2 Question… What happens to the ice cream you (or I!) eat?? What happens to the gasoline you put into your car? Do they just disappear? Ok, so where do their atoms go? They are rearranged into new substances!! So when we say weve used something up…have we?

3 Conservation neither be created nor destroyed –Law of Conservation of Matterin a chemical reaction, matter can neither be created nor destroyed – just rearranged. The numbers & kinds of atoms present in the products are the same as those in the reactants.The numbers & kinds of atoms present in the products are the same as those in the reactants. Balanced equations illustrate this law. Atoms are FOREVER!!

4 Why? (they can only be rearranged), mustChemical reactions cannot create or destroy atoms (they can only be rearranged), chemical equations must be balanced. reactants same number productThe atoms involved as reactants (Left of arrow) must still have the same number as on the product side (right of arrow), but they can be a part of new molecules.

5 2H 2 O =s 2 waters Coefficients(#s in front of compound) show how many of each compound is present. 2H 2 O =s 2 waters Atom Inventory List atoms in reactants and products under the arrow Determine the number of each atom. Subscriptsatoms Subscriptsshow a ratio of atoms to each other in a particular compound. H 2 O =s 2 hydrogens bonded to 1 oxygen NEVER Subscripts are NEVER changed when balancing! HH O HH O HH O

6 Example of Atom Inventory: CH 4 + 2 O 2 CO 2 + 2 H 2 O Reactants Products ____ C____ ____ H____ ____ O____ What does it mean if there is no coefficient in front of the compound? It is an implied 1! 1 1 44 44 Is this equation balanced? Yes!!!

7 Answers to BS 6 2 Methane gas (CH 4 ) reacts with oxygen gas (O 2 ) to produce carbon dioxide gas (CO 2 ) & water vapor (H 2 O) + + 1 C1 4 H4 4 O4 C H O Balanced! 3. HBr + Mg H 2 + MgBr 2 4Ag + 4H 2 S +O 2 2Ag 2 S + 4H 2 O Not Balanced! Close, but not yet Balanced!

8 5.Cellulose reacts with oxygen gas to form carbon dioxide gas & liquid water. C 6 H 10 O 5 + 6O 2 6CO 2 + 5H 2 O 6 C6 10 H10 17 O17 Balanced!!! 6.Nitroglycerin decomposes to form nitrogen gas, oxygen gas, carbon dioxide gas & water vapor 2 C 3 H 5 (NO 3 ) 3 3N 2 + O 2 + 6CO 2 + 5H 2 O 6 C6 10 H10 6 N6 18 O19 Not Balanced!

9 Steps to Balance atom inventory 1.Do an atom inventory. 2.Balanceusing coefficients 2.Balance by using coefficients to show multiple number of elements or compounds. NEVER change subscripts to balance (NEVER change subscripts to balance…is H 2 O the same as H 2 O 2 ? If so, would you like a big cold glass of hydrogen peroxide?!) in front of compound (Coefficients only inserted in front of compound, never split compound or the ratio would ) 3.Recount both sides.

10 Example: H 2 (g) + O 2 (g) H 2 O (l) 1.Atom Inventory: Reactants Products 2H22H2 2O12O1 2Insert coefficients to balance 3. Double check to make sure it is all BALANCED! 22 2 4 4

11 Reactants Products ____ Al____ ____ O____ Balance Al + O 2 Al 2 O 3 Do an atom inventory Use coefficient to multiply COMPOUND with element in it by # that balances it. 1 2 23 Is this equation balanced? No 3 -- 6 24 -- 4

12 Additional Rules Polyatomic ionsPolyatomic ions, (like NO 3 - and CO 3 2 -) that appear on both sides of equation should be balanced as units rather than balancing their atoms individually NO 3 NO 3 AgNO 3 + Cu ---> Cu(NO 3 ) 2 + Ag Balance atoms in pure elements w/ no subscripts last Recount all atoms one last time to be sure you are correct! 2 2

13 Balancing Equations For labs, demos, and whenever possible, indicate the states of each element or compound. –(s) solid (g) gas –(l) liquid (aq) aqueous Diatomic Elements? H O F Br I N ClH O F Br I N Cl Remember these elements need a subscript of 2 if in elemental state. If in compound then criss- cross charges to get subscripts

14 Practice NaCl + H 2 SO 4 Na 2 SO 4 + HCl 2 NaCl + H 2 SO 4 Na 2 SO 4 + 2 HCl 3 BaF 2 + 2 Al(OH) 3 3 Ba(OH) 2 + 2 AlF 3 2C 2 H 6 + 7O 2 4CO 2 + 6H 2 O (had to double everything to balance oxygen) BaF 2 + Al(OH) 3 Ba(OH) 2 + AlF 3 C 2 H 6 + O 2 CO 2 + H 2 O

15 Balanced Equations show Proportions Coefficients show how many of each compound reacts with, or creates another substance. Does that mean ONLY 2 hydrogen molecules will react with only 1 oxygen molecule? NO!! Could be 250 H 2 react with 125 O 2

16 2 H 2 molecules produce 2 H 2 O molecules 1 O 2 molecule produces 2 H 2 O molecules 2 H 2 molecules react with 1 O 2 molecules Example: 2 H 2 (g) + O 2 (g) 2 H 2 O (l)

17 Does that mean ONLY 2 hydrogen molecules will react with only 1 oxygen molecule? NO!! Could be 250 H 2 react with 125 O 2 Example: 2 H 2 (g) + O 2 (g) 2 H 2 O (l)

18 Types of Chemical Reactions SynthesisSynthesis DecompositionDecomposition Single replacement (displacement)Single replacement (displacement) Double replacement (displacement)Double replacement (displacement) CombustionCombustion A + B AB AB A + B ABAB A + BC AC + B ACAC AB + CD AD + CB C x H y + O 2 CO 2 + H 2 O N 2 + 3H 2 2NH 3 H 2 O 2 H 2 + O 2 Zn + 2HCl ZnCl 2 + H 2 NaCl + AgNO 3 NaNO 3 + AgCl CH 4 + 2O 2 CO 2 + 2H 2 O Examples ADAD A + BD BA + D

19 6. C 8 H 18 + O 2 CO 2 + H 2 O 89 16 +9 = 25 Os – to be put in pairs on the other side??? What could we do? Double everything…??? What you do to 1 thing, you have to do to everything… 2 1618 25


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