Chemistry Problems (Balancing Equations)

pg 293 #47

a) Pb(NO3)2(aq) + NaOH(aq) => Pb(OH)2(s) + NaNo3(aq)


This is the balanced equation
Pb(NO3)2(aq) + 2NaOH(aq) => Pb(OH)2(s) + 2NaNo3(aq)

problems worked in class

sorry about it being late, i experienced many technical difficulties but finally got them up so here are the problem that we worked in class

Blabble.

Is there no Blog for tonight? If not, sorry for the un-needed post. If so, hope this reminds someone. Oh, and Dr. B., were you able to find my HW #8? I have HW #9 for you as well, and tried to turn it in at the end of school on Friday, but you had already left. Sorry for the inconvience.

another day in chemistry by chris mathews

today we started the class with some superb singing by michael and joe krebs to the popular tune of the lion king. While most of the audience thought it was great, there are always a few critics. On the matter of chemistry we discussed how to properly solve problems that will be on our test. the test will be either tuesday or hopefully thursday of next week. Remember to do your homework tonight which is the worksheet, and to SHOW YOUR WORK!!!! also support the wrestling team in their closing season as they go for state. good luck all with you homework, call kyle for any questions

chris mathews

1/20/10 Assignment Posting

We did an example problem for Colby and talked about the chart of ways stoichiometry problems can be asked. Two bits of homework tonight: HW7 is p. 321-322 #26-30, and HW8 are these four problems.

15. When heated, sodium bicarbonate, NaHCO₃, decomposes into sodium carbonate, Na₂CO₃, water, and carbon dioxide. If 5.00g of NaHCO₃ decomposes, what is the mass of the carbon dioxide produced?

16. A reaction between hydrazine, N₂H₄, and dinitrogen tetroxide, N₂O₄, has been used to launch rockets into space. The reaction produces nitrogen gas and water vapor.

a. Write a balanced chemical equation for this reaction.

b. What is the mole ratio of N₂O₄ to N₂?

c. How many moles of N₂ will be produced if 20,000 mol of N₂H₄ are used by a rocket?

d. How many grams of H₂O are made when 450. Kg of N₂O₄ are consumed?

17. Joseph Priestly is credited with the discovery of oxygen. He produced O₂ by heating mercury (II) oxide, HgO, to decompose it into its elements. How many moles of oxygen could Priestly have produced if he had decomposed 517.84 g of mercury oxide?

18. Iron (III) chloride, FeCl₃, can be made by the reaction of iron with chlorine gas. How much iron, in grams, will be needed to completely react with 58.0 g of Cl₂?

Have a good night.

Tuesday, January 19, 2010

Today we did a few review problems from the book on using mole-ratio conversions.
We also learned about Actual Yield and Theoretical Yield and how to find the % Yield
There was an equation to how to find the % Yield

Act. Y. - Actual Yield
Th. Y. - Theoretical Yield

(Act. Y./Th. Y.) * 100 = % Yield

We have been asigned to do homework problems 165-175 on pg. 890 so get them things done to turn in before the bell rings on time. Please and Thank You.

Goody Night Get Homework Done!!!!!!

1/19/10

Limiting Reactants: the reactant that limits the amount of the other reactant that can combine and the amount of product that can form in a chemical reaction
Excess Reactant: substance that is not used up completely in a reaction

When solving problems with chemical reactions and converting grams to moles/ moles to grams/ etc., set up a single equation so that you only round once.

I Remembered

Stoichiometry Def.

• Composition stoichiometry deals with the mass relationships of elements in compounds.
• Reactions stoichiometry involves the mass relationship between reactants and products in a chemical reaction.

Know the 4 problem types

Mole Ratios

• A mole ratio is a conversion factor that relates the amounts in moles of any two substances involved in a chemical reaction.

Notes for Thursday, Jan. 14, 2010

Well, I don't know about you, but I could use some more blog credits so here are my notes for the day. They're pretty sparse because I take short notes when I'm not blogging, but it's better than nothing.

• Composition stoichiometry deals with the mass relationships of elements in compounds.
• Reaction stoichiometry involves the mass relationships between reactants and products in a chemical reaction.

There are four types of problems that were discussed in detail.

1. Amount of given substance (mol) --> amount of unknown substance (mol)
2. Amount of given substance (mol) --> amount of unknown substance (mol) --> amount of unknown substance (g)
3. Amount of given substance (g) --> amount of given substance (mol) --> amount of unknown substance (mol)
4. Amount of given substance (g) --> amount of given substance (mol) --> amount of unknown substance (mol) --> amount of unknown substance (g)

There could also be problems involving volume or formula units, but we didn't list those in the big four. There was a chart that's in the book, but I don't want to reproduce it. It could make a nice comment, though. Hint hint wink wink.

• A mole ratio relates the amount of moles of any substance involved in a chemical reaction.

Answers to Problems 5 and 6 on page 320

5. a. 5.0 mol H2

b. 2.5 mol O2

6. a. 15.8 mols O2

b. 9.0 mols CO2, and 13.5 mols H2O

Homework

HW 4: complete activity 3-11 from class.
HW5: complete problems 7-10 on page 320.

As always with a Jim Alrutz blog post, tomorrow's poster will be chosen with the power of random.org. Unless somebody wants to volunteer, with it being a three day weekend and all. By my watch it's past the standard blog post deadline, so I'm posting this. Good night, and have a pleasant tomorrow.

Wednesday, January 13, 2010

Today Dr. B reviewed over the homework that we turned in today. She went over most of the problems we had a hard time understanding, and she explained it to those who needed help with the problems. She showed us a trick in balancing chemical equations.

i.e. if carbon and hydrogen are one compound and a reactant and hydrogen has an even subscript then we should put 2 infront of carbon: 2C2H14

Thank God Dr. B postponed the test. Its not tomorrow so no need to cram tonite!!!!!!!

1/12/10

Today, Mr. Whittington talked to us about his AP Biology class and what to expect. He basically said the same things that Dr. Bautista said yesterday about AP Chemistry. After that, we reviewed some equations and balanced them in class. Ill do my best to illustrate it on this blog...

Unbalanced equation: C12 H22 O11 + O2----->12CO2+H2O
Balanced equation: C12 H22 12O11 +O2-----> 12CO2+11H20

This equation is a combustion because the equation yields CO2 and H2O

We will be having a test on THURSDAY so keep studying now since we also have an algebra test the same day!!!

Tonights HW: Pg. 292 #'s 37-47

January 11, 2010

Today Dr. B did not assign anyone to blog tonight, so I took it upon myself to go ahead and post what we did today in class. First we took a quiz over different types of reactions, then after we went over the quiz we used the remainder of the class time to discuss our choices for science courses next year. Our choices are AP Chemistry, AP Biology, and Physics. Tomorrow Mr. Whittington, a.k.a. The Godfather, a.k.a. The Don, will be coming into to class to tell us about AP Biology. Have a good night everyone.

chapter 8 section 2 continued

DECOMPOSITION REACTIONS
-in a decomp reaction, a single compound becomes two or ore simpler substances
-opposite of synthesis
-represented AX-->A + X
-AX is a compound
- A and X can be elements or compounds
- always smaller than AX

-decomp reactions with electricity are called hydrolysis
-2H2O-electricity-> 2H2 + O2
-Oxides of less reactive metals decompose into their elements when heated

-Decomp of acids
-certain acids decompose into nonmetal oxides and water
-carbonic acid readily dec0mposes at room temperature int CO2 and water

SINGLE-REPLACEMENT REACTIONS
-one element replaces a similar elemen i a compound
-many take place in aqueous solution
-A+BX-->AX+B or Y + BX -->BY + x
-most-active metals, Group 1, react with H2O to produce metal hydroxides and hydrogen
-less-active metals, example Iron, react with stea to form a metal oxide and hydrogen gas
-more-active metals react with certain acidic solutions, replacing hydrogen in acids
-products are a metal compound and hydrogen gas

-displacement of halogens
-fluorine is the most-active halogen
-in Group 17. each element ca replace any element below it, but none above it

DOUBLE-DISPLACEMENT REACTIONS
-ions of two compounds exchange place is an aqueous solution to from two new substances
-one of the compounds formed is usually a precipitate, gas, or a molecular compound
-AX+BY --> AY+BX
-A,X,B, &Y are ions
-AY & BX are ionic or molecular compounds

-formation of a precipitate
-cations of one compound combine anions of another
-form insoluble or slightly soluble compounds

COMBUSTION
-substances combine with oxygen, releasing large amounts of light and heat
-2H2+O2-->2H20
-C3H8+5O2-->3CO2+4H2O

**remember that the homework will be graded on correctness**

1/6/09

Today we took notes and talked about homework. The homework is P. 290 #'s 8, 10, 11, 13, 15, and 17. We also got a new worksheet handout but it is not due until a furthur date.

Notes

Section 2

Synthesis reactions

- In a synthesis reaction, also known as a composition reaction, 2 or more substances combine to form a new compound.

- This type of reaction is represented by the following equation.

- A + X= AX Where A and X can be elements or compounds and AX is a compound.

- Reactions of elements with oxygen and sulfur.

- One simple type of synthesis reaction is the combonation of an element with oxygen to produce an oxide of the element.

- Almost all metals react with oxygen to form oxides.

- Example: 2Mg(s) + O2(g) yeilds 2MgO(s)

- Group 2 elemets react in a similar manner, forming oxides with the formula MO, where M represents the metal.

- Group 1 metals form oxides with the formula M2O.

- Ex: Li2O

- The group 1 and group 2 elements react similarly with sulfur, forming sulfides with the formula M2S and MS, respectively.

16Rb(s) + S8(s) yields 8Rb2S(s)

8Ba(s) + S8(s) yields 8BaS(s)

- Nonmetals also undergo synthesis reactions with oxygen to form oxides.

- Ex: Sulfur reacts to form sulfur dioxide.

S8(s) + 802(g)

- Ex: Hydrogen reacts with oxygen to form digydrogen monoxide (water).

2H2(g) + O2(g) yields 2H2O(g)

- Reactions of metals with Halogens

- Most metals react with Group 17 elements, the halogens, to form either ionic or covalent compounds.

- Group 1 metals react with halogens to form ionic compounds with the formula MX where M is the metal and X is the halogen.

- Ex: 2Na(s) + Cl2(g) yields 2NaCl2

- Group 2 metals react with the halogens to form ionic compounds with the formula MX2.

- Ex: Mg(s) + F2(g) yields MgF2(s)

-Flourine is so reactive that it combines with almost all metals.

- Synthesis reactions with oxides

- Active metals are highley reactive.

- Oxides of active metals react with water to produce metal hydroxides.

- Ex: calcium oxide reacts with water to form calcium hydroxide.

CaO(s) + H2O(L) yields Ca(OH)2(s)

- Many oxides of nonmetals in the upper right of the periodic table react with water to produce oxyacids.

-Ex: SO2(g) + H2)(L) yields H2SO3(aq)

-Certain metals, oxides, and nonmetals oxides react with each other in synthesis reactions to form salts.

-Ex: CaO(s) + SO2(g) yields CaSo3(s).

Happy snow day I hope!!!!!!!!!!

Tuesday January 5

Characteristics of Chemical Equations

• Word and Formula Equations
• To balance an equation, begin by counting atoms of elements that are combined with atoms of other elements and that appear only once on each side of the equation

CH4 (g) + O2 (g) yields CO2 (g) + H2O (g) not balanced

• Begin by counting carbon atoms
• carbon is already balanced in the equation
• 2 additional hydrogen atoms are needed on the right side of the equation

CH4 (g) + O2 (g) yields CO2 (g) + 2H2O (g)

• now consider the number of oxygen atoms
• increase the number of oxygen atoms on the left side to 4 by placing the coefficient 2 in front of the molecular formula for oxygen
• The correct formula is

CH4 (g) +2O2 (g) yields CO2 (g) + 2H2O (g)

• arrow means "yields"
• two arrows means the equation is reversible
• (s) means the reactant or product is in a solid form
• a downward arrow is an alternative to (s, indicates a precipitate
• (l) is reactant or product in liquid form
• (aq) means it is dissolved in water
• (g) means it is a gas
• Arrow with a triangle or the word heat above it means that heat was added to the reactants
• arrow with the word pressure above it means pressure was applied during the reaction
• arrow with a temperature above it tells the temperature that reaction occured (no temperature is understood to be room temp)
• arrow with a chemical or element above it means that a catalyst was used to increase the rate of the reaction
• arrow with e- under it means electrolysis was used

sifnificance of a chemical equation

• some of the quantitative information revealed by a chemical reaction includes:

1. the coefficients of a chemical reaction indicate relative, not absolute, amounts of reactants and products
2. the relative masses of the reactants and products of a chemical reaction can be determined from the reaction's coefficients
3. the reverse for a chemical equation has the same relative amounts of substances as the forward reaction

• an equation does not indicate a reaction will occur
• an equation gives no info. about the speed of the reaction
• an equation does not give info. about changes in atom and ion bonds

Balancing chemical equations

• the following procedure demonstrates how to master balancing equations by inspection using step-by-step approach

1. Dr. B said it wasn't that important (and i never got it written down)
2. Write a formula equation by substituting correct formulas for the names of the reactants and the products
3. balance the formula equation according to the law of conservation of mass

• balance different types of atoms one at a time
• first balance the atoms of elements that are combined and that appear only once on each side of the equation
• balance polyatomic ions that appear on both sides of the equation as single units
• Balance H and O atoms after atoms of all other elements have been balanced

4. count atoms to make sure equation is balanced

• if the coefficients are not the smallest whole-number ratio, divide by the GCF in order to get the smallest whole-number ratio

Notes for Monday, Jan. 4, 2010

• A chemical reaction is the process by which one or more substances are changed into one or more different substances.
• In any chemical reaction, the original substances are known as the reactants and the resulting substances are known as the products.
• According to the law of conservation of mass, the total mass of the reactants must be equal to the total mass of the products for any given chemical reaction.
• A chemical equation represents, with symbols and formulas, the identities and relative molecular or molar amounts of the reactants and products in a chemical reaction.
• Example: The following chemical equation shows that the reactant ammonium dichromate yields the products nitrogen, chromium (II), and water.

(NH₄)₂Cr₂O_7- (s) --> N₂ (g) + Cr₂O₃ (s) + 4 H₂O (g)

• The symbols in parentheses state the form of the substance. q represents an aqueous substance. If a catalyst is needed to produce a reaction, it will be written with the arrow.

Indication of a Chemical Reaction

• Certain easily observed changes usually indicate that a chemical reaction has occurred.

1. Evolution of energy as heat and light.
2. Production of a gas
3. Color change
4. Formation of a precipitate.

• A solid that is produced as a result of a chemical reaction in a solution and that separates from the solution is known as a precipitate.

Characteristics of Chemical Equations

• The following requirements will aid you in writing and reading chemical equations correctly.

1. The equation must represent known facts.
2. The equation must contain the correct formulas for the reactants and products.
3. The law of conservation of mass must be satisfied.

• A coefficient is a small whole number that appears in front of a formula in a chemical equation.

Elements That Normally Exists as Diatomic Numbers

1. Hydrogen
2. Nitrogen
3. Oxygen
4. Fluorine
5. Chlorine
6. Bromine
7. Iodine

• Memory aid: seven elements, and the ones that aren't hydrogen form a seven on the periodic table.

Word and Formula Equations

• The first step in writing a chemical equation is to identify the facts to be represented.
• A word equation is an equation in which the reactants and products in a chemical reaction are represented by words.
• A word equation is qualitative.
• Example: methane + oxygen --> carbon dioxide + water.
• The next step in writing a correct chemical equation is to replace the names of the reactants and products with appropriate symbols and formulas.
• A formula equation represents the reactants and products of a chemical reaction by their symbols or formulas.

Example: CH₄ (g) + O₂ (g) --> CO₂ (g) + H₂O (g)

• To complete the process of writing a correct equation, the law of conservation of mass must be taken into account.
• The relative amounts of reactants and products represented in the equation must be adjusted so that the numbers and types of atoms are the same on both sides of the equation.
• This process is called balancing the equation and is carried out by inserting coefficients.

Once again, I'm going to give people the chance to volunteer to do tomorrow's blog or I'll use a random number generator to pick who gets it. Since lots of people asked me about this, feel free to check it out yourself at http://www.random.org/.

Have a good night,

Your Friendly Neighborhood Jim