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Balancing Chemical Equations. We’ve done it all – counted atoms, examined trends, bonded atoms…. But now, we’re going to string it all together in a sort.

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Presentation on theme: "Balancing Chemical Equations. We’ve done it all – counted atoms, examined trends, bonded atoms…. But now, we’re going to string it all together in a sort."— Presentation transcript:

1 Balancing Chemical Equations

2 We’ve done it all – counted atoms, examined trends, bonded atoms…. But now, we’re going to string it all together in a sort of equation. – Like math…but not math. Remember the conservation of mass? – Matter cannot be created or destroyed.

3 CHEMICAL EQUATIONS are representations of chemical reactions. – REACTANTS are the chemicals that go into the reaction. These are listed on the left side of the equation. – PRODUCTS are the chemicals that come out of the reaction. These are listed on the right side of the equation.

4 Chemical equations are written much like you would write a math problem. You’re basically adding things together to make a total on the right side. But there are some differences, too. – Instead of a “=“, we use an arrow to show direction (  ). – Sometimes equations aren’t as simple as adding things up.

5 Let’s look at an example. 2H 2 + O 2  2H 2 O This is the reaction to form water from its elements. What kinds of terms or features do you notice in this equation? What are my reactants? What are my products?

6 2H 2 + O 2  2H 2 O In the formation of water (H 2 O), we react, or consume, 2 portions of hydrogen for every 1 portion of oxygen. As a result, we produce 2 portions of water. Let’s look at the atoms themselves. – Is this equation BALANCED? Are all the atoms that start the reaction present at the end? – 4 hydrogen go in, 4 hydrogen come out – 2 oxygen go in, 2 oxygen come out

7 Try another example: CH 4 + 2O 2  CO 2 + 2H 2 O This is the reaction for burning methane. Notice that one of the products is carbon dioxide, a greenhouse gas.

8 CH 4 + 2O 2  CO 2 + 2H 2 O How many carbons do we start with? – How many do we end with? How many hydrogens do we start with? – How many do we end with? How many oxygens do we start with? – How many do we end with? This equation has already been balanced for you. Let’s see if you can balance one on your own.

9 ___Na + ___H 2 O  ___NaOH + ___H 2 This is the reaction for sodium metal with water. How can you balance this reaction?

10 Now I will provide an equation that is balanced, but is missing the product’s formula. Can you predict the product of this reaction? C 6 H 12 O O 2  6 CO _______

11 Predict the product Given the reactants, predict the product in these reactions. 2 Fe + Cl 2  _________ 2 P + 2 O 2  __________ Ca + S  _________ 2 C + 2 H 2  __________ Are these products ionic or covalent? Can you draw out the product on the fourth example?

12 Sodium hydroxide (NaOH) is a potent base that draws water and carbon dioxide out of the air if left in the open. It is also a base used to neutralize certain acids. ___ NaOH + ___ CO 2  ___ Na 2 CO 3 + ___ H 2 O ___ NaOH + ___ HCl  ___ NaCl + ___ H 2 O

13 Indiana is well known for its limestone, harvested around Bloomington. Limestone is a hard deposit (mostly calcium carbonate) that was likely deposited by marine life. Limestone is used in building, but has stopped being used for monuments in densely-populated areas. Humans have a large impact on the environment, with waste producing phenomena like smog and acid rain.

14 A reaction for dissolving calcium carbonate is: ___CaCO 3 + ___HCl  ___H 2 O + ___CO 2 + ___CaCl 2 Why might limestone be a poor building material choice for densely-populated cities like Los Angeles or New York City? Acid rain eats away at the faces of limestone buildings, eroding the strength of the building. FYI - The product, calcium chloride (CaCl 2 ), is used as salt for roads (rock salt) and water hardeners.

15 Individual/Small group Practice Practice with a partner or individually on balancing some chemical equations. For each of the problems, find ALL of the coefficients to balance the equation. – Aim for 10 basic and % – For extra practice, go for the mastery problems – I know they won’t all fit on the worksheet. Just fill in the first 13, then work on scrap paper. – Write down your problems on the worksheet and turn it in at the end of class.

16 Basic problems CH 4 + O 2  CO 2 + H 2 OKClO 3 → KCl + O 2 H 2 + O 2 → H 2 OP 4 + O 2 → P 2 O 5 Al + Br 2 → AlBr 3 CCl 4 +O 2  CO 2 +Cl 2 C 3 H 8 + O 2  CO 2 + H 2 OSnO 2 + H 2 → Sn + H 2 O C 6 H 6 + O 2 → CO 2 + H 2 OAgI + Na 2 S → Ag 2 S + NaI Advanced problems Na + C 2 Cl 6 → NaCl + C 2 Cl 2 C 2 H 6 + O 2  CO 2 + H 2 O C 2 H 3 Br 3 +O 2  CO 2 +HBrP 4 + HCl + O 2 → PCl 3 + H 2 O AlBr 3 + Cl 2 → AlCl 3 + Br 2 C 6 H 5 F+O 2  CO 2 +H 2 O+F 2 CaCN 2 +H 2 O  CaCO 3 +NH 3 TiCl 4 + H 2 O → TiO 2 + HCl C 6 O 6 Cr + Cl 2 → CrCl 3 + CO Mastery problems AlI 3 + HgCl 2 → AlCl 3 + HgI 2 HSiCl 3 + H 2 O  H 10 Si 10 O 15 + HCl KOH + H 3 PO 4 → K 3 PO 4 + H 2 OBa 3 N 2 + H 2 O → Ba(OH) 2 + NH 3 Ca(OH) 2 + H 3 PO 4 → Ca 3 (PO 4 ) 2 + H 2 ONH 3 + CO → CH 4 + N 2 + O 2 AgNO 3 + K 3 PO 4 → Ag 3 PO 4 + KNO 3 C 7 H 9 + HNO 3  C 7 H 6 (NO 2 ) 3 + H 2 O


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