750 likes | 1.18k Views
Reminders!!!!!!!!!. As I have said many time over the last few weeks? ASK QUESTIONS? ASK ME TO SLOW DOWN!!!!I know this stuff? You don't? Make sure you tell me when to slow down and go over something again!Do not forget vocabulary will be due on the day of your chapter eight test!!!!!!!9 Terms fo
E N D
1. Chemical Equations andReactions Chemistry
Chapter 8
2/23/09
2. Reminders!!!!!!!!! As I have said many time over the last few weeks… ASK QUESTIONS… ASK ME TO SLOW DOWN!!!!
I know this stuff… You don’t… Make sure you tell me when to slow down and go over something again!
Do not forget vocabulary will be due on the day of your chapter eight test!!!!!!!
9 Terms for 9points
3. What do you know? What are some signs that a chemical change may be taking place?
What are the reactants of a reaction? What are the products of a reaction?
Describe the law of conservation of mass.
What are some types of reactions that we talked about before winter break?
4. Here’s What I Know Formation of a gas or solid, change in color or odor, and release/absorption of energy
Reactants are what you start with and products are what you form
Law of conservation of mass means however much mass you start with you must end with
We talked about synthesis, decomposition, single and double replacement reactions
5. Check This Out! 5g of baking soda
5mL of vinegar
Total mass=_______
Now I will pop the top and we will see what happens
Final Total mass=________
6. Describing Chemical ReactionsSection One Goals List evidence that suggests that a chemical reaction has occurred
Describe a chemical reaction by using a word equation and a formula equation
Interpret notations in formula equations, such as those relating to states of matter or reaction conditions
7. Chemical Change Give me a few examples of CHEMICAL change
Chemical reaction=> the process by which one or more substances change to produce one or more different substances
Atoms do not become other types of atoms nor do they appear or disappear
The bonding patterns among the atoms are merely rearranged
8. Reactants vs. Products Reactants are what you start with or the “original substances”
Products are what you end up with or the “new substances”
Example:
Camp fire- reactants: wood and fire/match… products: carbon dioxide and water
9. Evidence of a Chemical Change Change in energy
Release of heat
Release of light
Production of sound
Change in temperature
Change in electrical energy
Formation of a new substance
Formation of a gas
Formation of a precipitate (solid)
Change in color
Change in odor
10. Chemical Reaction vs. Physical Change Only way to know for sure that an actual chemical reaction has taken place is to do a chemical analysis on the products
These test would show that the new substances’ density, melting point or boiling point are different then the reactants’
11. Examples Even though you have a color change when you mix paints, the final chemical composition is still the same as when you started (physical change)
Copper reacting with nitric acid also has a color change, but it is a chemical change because you end up with two totally different products
12. Reactions and Energy Changes Reactions can gain or lose energy
methane + oxygen -> carbon dioxide + water + energy
Energy is released it is a product (exothermic)
Dinitrogen tetroxide + energy -> nitrogen dioxide
Energy is absorbed it is a reactant (endothermic)
13. More on Energy Changes Exothermic reactions yield stronger bonds
This is because the bonds holding the products together are stronger than those in the reactants
The stronger the bond the more energy released when bond forms and more energy to break more bonds in the reactants
14. One Last Thing On Energy
15. Do You Remember? For a reaction to take place the reactants actually have to…
Come into contact with each other
Example: the potassium chlorate on match heads must contact the phosphorus on the matchbox
16. Chemical Equation A representation of a chemical reaction that uses symbols to show the relationship between the reactants and the products
Must obey the law of conservation of mass
Number of atoms on each side of the arrow must be the same
17. Writing a Word Equation Follow the steps to get it right!
1) Write down the names of the reactants
2) Put a plus sign between any reactants
3) Draw an arrow to the left of the reactants
4) Write down the names of the products after the arrow
5) Place a plus sign between any products
18. Try This! Methane reacts with oxygen to form carbon dioxide and water
Make this a word equation (Follow the steps!)
methane + oxygen -> carbon dioxide + water
19. Writing a Formula Equation Follow these steps
1) Replace the formulas for the names in the word equation
2) Put a question mark (?) in front of each formula
3) Even out the number of atoms of each element on each side by replacing the (?) with numbers
20. Few Tips 1) Delay the balancing of elements (often H and O) that occur in several reactants or products
2) If the same polyatomic ions appear on both sides of the equation, treat them as single units, like monatomic ions
3) After using steps 1&2, balance the elements left to right
4) Remember, balancing one element may unbalance others (So ALWAYS double check at the end!!!)
5) For ionic equations, be sure charges are balanced (If/when we use these)
21. Try This One! methane + oxygen -> carbon dioxide + water
Make this a formula equation
?CH4 + ?O2 -> ?CO2 + ?H2O
CH4 + 2O2 -> CO2 + 2H2O
22. So… What Do All the Number Mean?
23. Important Information Chemical equations tell more than just what is used and made in a reaction
Shows how much of everything is in a reaction
Tells temperature and/or pressure needed for the reaction
24. Check This Out! NaHCO3(s) + HC2H3O2(aq) -> NaC2H3O2(aq) + CO2(g) + H2O(l)
N2(g) + 3H2(g) 350°C, 25,000kPa 2NH3(g)
catalyst
Tells a little bit about each compound in the reaction
25. State Symbols and Reaction Conditions Open your book to page 265
Table 2 is a list of many symbols that you will need to know/use for writing equations
26. How About Now? List evidence that suggests that a chemical reaction has occurred
Describe a chemical reaction by using a word equation and a formula equation
Interpret notations in formula equations, such as those relating to states of matter or reaction conditions
27. “Balancing Chemical Equations”Section Two Goals Relate the conservation of mass to the rearrangement of atoms in a chemical reaction
Write and interpret a balanced chemical equation
28. Conservation of Mass In ordinary chemical or physical changes, mass is neither created nor destroyed
Think back to the demonstration I did with the baking soda and vinegar
The mass of everything I started with was the same as what I ended with
29. Not Making New Atoms Remember we said that all we are doing is rearranging the atoms not making new atoms
For this reason our mass does not change only the compounds we have change
You can also tell this by looking at balanced equations
2Na + 2H2O -> 2NaOH + H2
The types of atoms we start with are the same types we end with
30. Balancing EquationsDo You Remember???? Number on left side of the arrow must equal the number on the right side of the arrow
Hence the balance part of balanced equations
We can only change the coefficients
Coefficient=> a small whole number that appears as a factor in front of a formula in a chemical equation
H20 compared to 2H2O
3Ca(NO3)2
31. One More Time Here’s how to do it:
1) Identify reactants and products
2) Count atoms
3) Insert coefficients
4) Check your final answer
32. Sample Problem APage 269 Balance the equation for the reaction of iron(III)oxide with hydrogen to form iron and water.
1) Identify reactants and products
Fe2O3 + H2 -> Fe + H2O
2) Count atoms
Make a chart
3) Insert coefficients
Fe2O3 + 3H2 -> 2Fe + 3H2O
4) Check final answer
Fix chart to match the coefficients you used in step 3 and make sure everything is even
33. Your Turn Try numbers 2 and 3 on page 269
Make sure to follow the steps!!!
34. Never Ever Ever!!!!! DO NOT CHANGE SUBSCRIPTS
If you change these your are changing the compounds in the reactions!!!
We can only change the coefficients to make the number of atoms balance
When we change these we are just changing the number of moles of the substance needed in the reaction
35. “Odd-Even Technique”Sample Problem BPage 271 The reaction of ammonia with oxygen produces nitrogen monoxide and water vapor. Write the balanced equation for this reaction.
1) NH3 + O2 -> NO + H2O
2)
**When using the odd-even we know that an odd number multiplied by 2 gives us an even number
3) 4NH3 + 5O2 -> 4NO + 6H2O
4) Double Check
36. Your Turn! Try numbers 2&3 of Sample Problem B page 271
37. Polyatomic Ions and Balancing Sometimes a polyatomic ion will stay intact throughout the reaction so when we go to balance the equation we can think of it as its own “atom”
Example:
2Al + 3H2SO4 -> Al2(SO4)3 + 3H2
38. Sample Problem CPage 273 Aluminum reacts with arsenic acid(HAsO3), to form H2 and aluminum arsenate. Write a balanced equation for this reaction.
Al + HAsO3 -> H2 + Al (AsO3)3
2Al + 6HAsO3 -> 3H2 + 2Al (AsO3)3
39. Your Turn! Try number 1&2 on page 273
40. “Classifying Chemical Reactions”Section 3Goals Identify combustion reactions, and write chemical equations that predict the products
Identify synthesis reactions, and write chemical equations that predict the products
Identify decomposition reactions, and write chemical equations that predict the products
Identify displacement reactions and use the activity series to write chemical equations that predict the products
Identify double-replacement reactions, and write chemical equations that predict the products
41. Types of Reactions We classify reactions to make predicting the products easier
Each type of reaction follows a certain pattern which make balancing easier:)
42. As AlwaysThere’s a Catch The 5 reactions we talk about are not the only types
Each reaction does not have to fit into just one type
Maybe more than one maybe none
43. Combustion Reactions Combustion reaction=> reaction of a carbon-based compound with oxygen
Products are carbon dioxide and water vapor
Used to generate energy
Ex: the lighting in here is because of the combustion of coal
Do you have any others?
44. Hydrocarbons Just a fancy way to say the compound only has hydrogen and carbon in it
Example: Propane
C3H8 + 5O2 -> 3CO2 + 4H2O
45. Alcohols Made of carbon, hydrogen, and oxygen
Products are still only carbon dioxide and water vapor
Example: Ethanol
CH3CH2OH + 3O2 -> 2CO2 + 3H2O
46. How Do We Get Soot? Anytime we have combustion reaction that does not have enough oxygen then we end up with soot (unburned carbon) and carbon
We also end up with carbon dioxide and water vapor
47. Synthesis Reactions Synthesis means “to put together” so…
Synthesis Reaction=> a single compound forms from two or more reactants
Indicator: if you only have one product or if you only have two elements or small compounds as reactants
48. Binary Compound Composed of two elements
The left side of the periodic table wants to react with the right side of the table
Isn’t always easy to tell what compound will form at the end
Example: Carbon and Oxygen
49. Ternary Compound Two compounds combine to form a ternary compound
Compound of three elements
Example: CaO + H2O -> Ca(OH)2(s)
50. Decomposition Reactions Decomposition Reaction=> a single compound breaks down into two or more elements or simpler compounds
Opposite of synthesis reactions
Often need an input of energy to make the reaction happen
51. Examples Often when you start with a binary compound you end up with the two elements that made up your reactant
Water
We use the gases from water in hospitals… very expensive because of the energy needed to make the decomposition happen
52. Cool Fact We are now trying to make solar cells that will be able to give the energy needed to break apart water
53. Sample Problem DPage 279 Predicting Products
Let’s try them together!!!
54. Displacement Reactions Metals can replace metals or hydrogen
Nonmetals can replace nonmetals
In these reactions a single element reacts with a compound and displaces another element from the compound
Like they switch places
55. Activity Series Activity series=> a series of elements that have similar properties and that are arranged in descending order of chemical activity
Page 281 Table 4 “Activity Series”
Appendix A has a more complete table!!!
56. More on Activity Series Elements can only “switch” places with elements below it on the activity series
57. How To… (Page 281) 1) Identify the reactants
Determine if element is metal or halogen
Determine the element that might be displaced from compound
2) Check the activity series
Determine which element is more active
3) Write the products and balance the equation
If the more active element is already part of the compound then NO reaction will happen
4) Verify your results
Make sure the equation is balanced (just like always)
58. Sample Problem E Let’s try one together
Your turn!!!!
59. Double- Displacement Reactions Double- Displacement Reaction=> a reaction in which a gas, a solid precipitate, or a molecular compound forms from the apparent exchange of atoms or ions between two compounds
Happens in aqueous solutions
Must end up with a solid precipitate, gas, or molecular compound (like water)
60. Side Note In double- displacement reactions water, as a product, is often written as HOH so you can more easily see the exchange of atoms/compounds
61. Example HCl(aq) + NaOH(aq) -> HOH(l) + NaCl(aq)
Notice how I put HOH
This is a double replacement reaction
The H and the Na changed partners
You formed water (that’s one of the signs!!)
62. Skills Toolkit Page 284 Use this chart to help you identify reactions and predict products
63. “Writing Net Ionic Equations”Section 4 Goals Write total ionic equations for reactions in aqueous solutions
Identify spectator ions and write ionic equations for reactions in aqueous solutions
64. Ionic Equations When ionic compounds dissolve in water, the ions separate form each other and spread throughout the solution
So when you see KI(aq) what it really means is K+(aq) + I-(aq)
Or if you see Pb(NO3)2(aq) it means Pb+2(aq) + 2NO3-(aq)
65. More Correct When we react the two compounds on the last slide we would do this:
KI(aq)+ Pb(NO3)2(aq) -> PbI2(s) + 2KNO3(aq)
But we should put the charges on them and then balance the charges and masses
K+(aq) + I-(aq) + Pb+2(aq) + 2NO3-(aq) -> PbI2(s) + 2K+ (aq) + 2NO3-(aq)
66. Most Correct When you mix two solutions all of the ions are present in the combined solution
But not all of the ions will react with each other
Spectator ions=> ions that are present in a solution in which a reaction is taking place but that do not participate in the reaction
These spectator ions can be taken out of the total ionic equation
67. Example Bottom of page 286
68. Writing Net Ionic Equations These equations only show the compounds that change
69. Displacement Net Ionic Happens in displacement reactions too
Zn(s)+Cu+2(aq)+SO4-2(aq)-> Cu(s)+Zn+2 (aq)+ SO4-2(aq)
Which is the spectator ion?
How would we correctly write this?
70. Skills Toolkit Page 288 1) List what you know
ID each chemical described
ID type of reaction
2) Write a balanced equation
Predict products
Include states (next slide shows how to know!!!)
3) Write total ionic equation
Write separated aqueous ions for each aqueous ionic substance
DO NOT split up anything that is a solid, liquid, or gas
4) Find the net ionic equation
Cancel out spectator ions
Double check numbers and charges
71. Solubility All group 1 compounds and NH4
All nitrates
All halides (but Ag+ and Pb+2)
All sulfates (but Ca+2, Sr+2, Ba+2, Hg+2, and Pb+2)
All carbonates (except group 1 and NH4) are INSOLUBLE!
72. Charges Make sure charges are equal on both sides
SO4-2 (aq) + Ba+2 (aq) -> BaSO4(s)
Notice no charge on reactant side so no charge on product side
73. Practice Br2(l) + NaI(aq) -> NaBr(aq) + I(s)
Br2(l) + 2Na+(aq) + 2I-(aq) -> 2Na+(aq) + 2Br-(aq) + I2(s)