Week of Tuesday January 15th 2002
Chapter 24 Notes
Section 1 Chemical Changes
A. Describing chemical reactions--change of one or more substances converted into new substances.
1. Reactants are substacnces that combine or change.
2. New substances that are produced are called products.
B. Conservation of Mass--a law which states that, in a chemical reaction, matter is not created or destroyed; it stays the same.
1. Antoine Lavoisier--experimented with mercury (II) oxide and heat.
2. Found mass of products (liquid mercury and oxygen gas) equaled mass of reactants.
C. Writing equations--a chemical equation uses chemical formulas and symbols to describe a chemical reaction and the product(s) it produces.
1. Chemical formula expresses the relationship between elements in the compounds and molecules they make up.
2. Coefficients--numbers which represent the number of units of each substance in a reaction.
3. Knowing coefficients of chemical reactions allows chemists to use the correct amounts of reactants to predict the amounts of products.
4. Subscripts--numbers which represent the number of atoms in a molecule of a particular element.
5. Symbols used to show state of reactants: (s)solid, (aq)aqueous, (g)gas, (l)liquid.
D. Metals react with atmosphere in different ways.
DISCUSSION QUESTION:
Why are coefficients important?
Section 2 Chemical Equations
A. Checking for balance--law of conservation of mass requirement.
1. A balanced chemical reaction--both sides of equation have same number of atoms of each element.
2. Choosing coefficients--becomes easier with practice; trial and error at first.
B. Writing balanced chemical equations--a four-step process.
1. Describe the reaction in words.
2. Write the equation using formulas and symbols.
3. Check for balance.
4. Add coefficients where needed for balance.
DISCUSSION QUESTION:
Why do chemical equations need to be balance?
Section 3 Classifying Chemical Reactions
A. Synthesis reaction--two or more substance form a new substance; A+B -> C.
B. One substance breaks down into two or more substances in a decomposition reaction; AB -> A+B
C. Single-Displacement reaction--one element replaces another one in a compound; A+BC->AC+B or D+BC->BD+C
D. A double-displacement reaction results if a precipitate, water, or gas forms when two ionic compounds in solution are combined; AB+CD->AD+CB
DISCUSSION QUESTION:
What two chemical reactions are "opposites" of each other and why?
Section 4 Chemical reactions and energy
A. Chemical recations involve energy exchange
1. Breaking chemical bonds requires energy
2. Forming chemical bonds releases energy
B. More energy out
1. Exergenic reactions-energy required to break bonds is less than the energy released from new bonds; energy given off is usually light
2. Exothermic reactions-energy given off in the form of heat.
C. More energy in
1. Endothermic reactions-more energy is required to break bonds than to form new ones; need energy for the reaction to occur
2. If energy is needed is heat the reaction is endothermic
3. A catalyst speeds up a chemical recation without itself being permanently changed.
4. An inhibitor prevents or slows a chemical reaction or interfers with a catalyst's action.
Discussion Question:
How are chemical bonds involved in energy exchanges? (Breaking bonds requires energy; forming bonds releases energy)
Chapter 2: Section 1 Describing motion
A)MOTION-When an object changes it's position realitive to a refrence point.
1)DISTANCE-how far an object has moved.
2)DISPLACEMENT-distance and direction of a objects change of position from a starting point.
B)SPEED-distance an object moved per unit of time.
1)RATE-any change over time.
2)calculation for speed :speed=distance/time.
3)speed that dosent change over time is constant speed.
4)speed is usually not cnstant,usually an object has changing speed.
5)AVERAGE SPEED-speed of motion wen speed is changing:speed=total ditance/total travel time.
6)INSTANTANEOUS SPEED-speed at any given point in time.
C)a distance-time graph displays motion of an object over time.
1)plot distance on a (n)vertical axis.
2)plot time on a(n)horizontal axis.
D)VELOCITY-speed and direction of an objects motion.
E)motion of eraths crust- so slow we dont notice!!
DISCUSSION QUESTION: how do changing speed and constant speed differ?
SECTION 2 ACCLERATION
A) accleration- change in velocity rate.
1)positive accleration- speed incresing
2)negitive accleration- speed decresing
3)when an object changes speed or direction it is accleration.
B)Calculating acceleration
1)accleration= change in velocity/time.
2) change in velocity=final velocity-initial velocity.
3)unit for accleration- meters per second squared
4)positive accleration-positive slope on a velocity time graph.
5)negitive accleration- negitive slope on a velocity time graph.
C)amusment park accleration- roller coster
1)changes in speed cause accleration.
2)changes n direction cause accleration.
DISCUSSION QUESTION: IS A WOODEN ROLLER COSTER SWAYING ACCLERATION. WHY OR WHY NOT?
joke: Science Project
A freshman at Eagle Rock Junior High won first prize at the Greater Idaho Falls Science fair. He was attempting to show how conditioned we have become to alarmists practicing junk science and spreading fear of everything in our environment.
In his project he urged people to sign a petition demanding strict control or total elimination of the chemical “dihydrogen monoxide.” And for plenty of good reasons:
1. It can cause excessive sweating and vomiting
2. It is a major component of acid rain
3. It can cause severe burns in its gaseous state
4. Accidental inhalation can kill you
5. It contributes to erosion
6. It decreases effectiveness of automobile brakes
7. It has been found in tumors of terminal cancer
He asked fifty people if they supported a ban of the chemical.
Forty-three said yes and six were undecided. Only one knew that the chemical, “dihydrogen monoxide” was water. The title of his prize winning project was, “How Gullible are We?” He feels the conclusion is obvious
CHAPTER 25
SECTION 1: ACIDS and BASES
A. Acid-contains at least one hydrogen atom that can be removed when acid is dissolved in water, forming hydronium ions
B. Properties of acids
1. taste sour
2. corrosive and can damage skin or tissue
3. react with an indicator such as litmus paper to produce a predictable color change
C. Common acids
a. Foods contain acids
b. yogurt and buttermilk have lactic acid
c. vinegar, or acetic acid, is in pickled foods
2. the stomach uses hydrochloric acid
3. four acids are vital to industry
a. sulfuric acid is used in car batteries and the manufacturing of fertilizers
b. phosphoric acid is used to manufacture detergents, fertilizers, and soft drinks
c. nitric acid is used to manufacture fertilizers and explosives
d. steel can be cleaned with hydrochloric acid.
D. Base-a substance that forms hydroxide ions in a water solution; also accepts hydronium ions from acids
E. Properties of bases
1. many are crystalline solids in pure undissolved state
2. feel slippery in solution
3. strong bases are corrosive
4. react with indicators to produce predictable color changes; litmus paper turns blue
F. Common bases are used in cleaning products, medications, fabrics, and deodorants
G. Solutions of acids and bases
1. acid describes compounds that can be ionized in water to form hydronium ions
2. base describes compounds that can form hydroxide ions in solution
3. solutions of acids and solutions of bases are electric conductors to some extent
DISCUSSION QUESTION: Why should a person never use a taste test to identify an acid or a base?
SECTION 2: Strength of acids and bases
A. the strength of an acid or base depends on how completely a compound separates into ions when dissolved in water
1. a strong acid ionizes almost completely in solution
2. a weak acid only partly ionizes in solution
3. a strong base dissociates completely in solution
4. a weak base does not ionize completely
5. strong acids and bases conduct more electricity than weak ones
6. equations for stong acids and bases use a single arrow, indicating ions are formed
7. equations for weak acids and bases use double arrows pointing in opposite directions, indicating an imcomplete reaction.
8. dilute and concentrated are terms to describe the amount of acid or base dissolved
B. pH of a solution
1. pH is a measure of the concentration of H+ions in a solution or how acidic or basic it is.
a. pH lower htan 7 means acidic
b. pH greater than 7 means basic
c. pH exactly 7 indicates a neutral solution
2. pH is determined using a universal indicator paper or pH meter
3. blood contains buffers which keep the pH in the blood balanced at about 7.4
DISCUSSION QUESTION: is a strong acid the same thing as a concentrated acid? why or why not?
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