11/30/10http://teachers.yourhomework.com/blowe/1 Today's Agenda.t 11/30/10 Recall – Names Intro to Unit 5 Reactions Balancing Chemical Equations

Recall! Write out the compounds for the following: 1.Sodium Chloride 2.Sodium Sulphide 3.Calcium Bromide 4.Lithium Oxide 5.Dihydrogen Monoxide 6.Nitrogen Trioxide 11/30/10http://teachers.yourhomework.com/blowe/2 NaCl Na 2 S CaBr 2 Li 2 O H2OH2O NO 3

Unit 5 Intro Describing Chemical Reactions: In a chemical reaction, atoms rearrange to form new substances A Chemical analysis is the only way to prove that a reaction has occurred. Symbols are used in chemical equations to identify the physical states of substances and the physical conditions during a chemical reaction 11/30/10http://teachers.yourhomework.com/blowe/3

Evidence of Change Changes in Energy: Release of energy, Heat or Light Production of Sound Reduction of temperature Absorption or release of electrical energy Formation of new substances: Formation of Gas or Precipitate (liquid or solid) Change in Odor Change in Color 11/30/10http://teachers.yourhomework.com/blowe/4

Key Terms Chemical Reaction – The process by which one or more substances changes to produce one or more different substances. Chemical Equation – A representation of a chemical reaction that uses symbols to show the relationship between the reactants and the products. 11/30/10http://teachers.yourhomework.com/blowe/5

Writing a word equation or a formula Equation Ex. methane + oxygen  carbon dioxide + water Convert this word equation into a formula equation: Look up what Methane is in the book (CH 4 ). Oxygen is a gas so you must use (O 2 ). From the name carbon dioxide we write (CO 2 ). And we know what water is, (H 2 O) 11/30/10http://teachers.yourhomework.com/blowe/6 Halfway

Writing a word equation or a formula Equation continued Ex. CH 4 + O 2  CO 2 + H 2 O But there is an imbalance! See how there is 4 H’s on the left side and 2 H’s on the right? 11/30/10http://teachers.yourhomework.com/blowe/7 4 H’s2 H’s Because of the law of conservation of matter, there must be an equal amount of atoms of each element on each side of the equation. So we really have ?CH 4 + ?O 2  ?CO 2 + ?H 2 O

Writing a word equation or a formula Equation continued Ex. ?CH 4 + ?O 2  ?CO 2 + ?H 2 O Where to start? Take a look at each compound. (C) is good for now, one on each side. There is 2 oxygen on the left and 3 on the right. That might be hard to balance first. Lets start with Hydrogen 11/30/10http://teachers.yourhomework.com/blowe/8 ?CH 4 + ?O 2  ?CO 2 + ?H 2 O ?CH 4 + ?O 2  ?CO 2 + 2H 2 O Now we got 4 H’s on both sides

Writing a word equation or a formula Equation continued Ex. ?CH 4 + ?O 2  ?CO 2 + 2H 2 O We have 4 H’s but now we have 4 O’s on the Right side. 11/30/10http://teachers.yourhomework.com/blowe/9 Now we must make the left side have 4 O’s By multiplying O 2 by 2 to get 4 O’s 4 O’s ?CH 4 + 2O 2  ?CO 2 + 2H 2 O 4 O’s

Writing a word equation or a formula Equation continued Ex. ?CH 4 + 2O 2  ?CO 2 + 2H 2 O Now Carbon is good so the final ?’s can be changed to 1 and you leave them out. 1CH 4 + 2O 2  1CO 2 + 2H 2 O CH 4 + 2O 2  CO 2 + 2H 2 O 11/30/10http://teachers.yourhomework.com/blowe/10

Final tips Remember distributive properties! (When the number is in front). They are a little wired in Chemistry. 2H 2 O means 4 H’s and 2 O’s Using parentheses is also the same thing but avoid writing equations like this: (H 2 O) 2 means 4 H’s and 2 O’s as well. With these problems, you go back and forth on both sides of the equal sign. That’s why it’s called balancing! 11/30/10http://teachers.yourhomework.com/blowe/11

Homework Half–worksheet copied into your composition book. 5 problems, and I also wrote the chemical symbols for you. This can be really quick. All done for a Stamp tomorrow I’ll stamp MythBusters facts/chemical reactions now. 11/30/10http://teachers.yourhomework.com/blowe/12