Chemical Reactions


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  • Francium is also suspected to have a melting point of 80 degrees Farenheit, but Francium is a highly radioactive metal that decays into astatine, radium, and radon.
    Bulk francium has never been viewed. Because of the general appearance of the other elements in its periodic table column, it is assumed that francium would appear as a highly reflective metal, if enough could be collected together to be viewed as a bulk solid or liquid. Obtaining such a sample is highly improbable, since the extreme heat of decay (the half-life of its longest-lived isotope is only 22 minutes) would immediately vaporize any viewable quantity of the element.
    As little as 20–30 g (one ounce) exists at any given time throughout the Earth's crust; the other isotopes (except for francium-221) are entirely synthetic. The largest amount produced in the laboratory was a cluster of more than 300,000 atoms.
  • Like the days of the month, the chemical elements can be arranged in a way that shows a repeating, or PERIODIC pattern.
    Patterns: atomic # increases as you move left to right
    Groups share same # of valence electron
    Energy levels increase as you move down a group
  • chalk = calcium carbonite (CaCH3)
    ammonia = NH3
  • Why are most elements found as a combination of several different atoms joined together into compounds?
  • Why are most elements found as a combination of several different atoms joined together into compounds?
  • Remember: a substance is an element or compound. New elements are not FORMED in reactions.
    ***The (g) is for gas and (l) is for liquid
    coefficients tell how many molecules of each substance are involved in each reaction - no coefficient means there is just ONE molecule
  • Beauty salon peroxide to show how difference in concentration affects rate of reaction
  • C6H12O6 + O2 = CO2 + H2O is the reaction in your body's cells that turn sugar and oxygen into usable energy (ATP), with CO2 and water as waste products
    ***reaction is reversed in plants (sugars are created from water and CO2 with sunlight's energy)
  • A catalyst is a substance that speeds up a reaction without being used up itself.
    Here is an example of a reaction with a catalyst. Hydrogen peroxide decomposes (falls apart) to form water and oxygen gas:
    hydrogen peroxide —> water + oxygen
    This reaction only occurs very slowly unless we add the compound manganese oxide that acts as a catalyst for this reaction. When the catalyst is added the reaction speeds up greatly but the manganese oxide never runs out.
    How does a catalyst work?
    1) A catalyst provides a surface on which the reaction can take place. This increases the number of collisions between the particles of the substances that are reacting.
    2) A catalyst lowers the activation energy (the minimum amount of energy needed for a reaction to take place). This means that the particles can react with less energy than they needed before the catalyst was added. If we lower the amount of energy needed for particles to react, then more particles can react.
  • C 3H8 = propane
  • Use Beauty salon peroxide to show how difference in concentration affects rate of reaction
    Have students put on their safety glasses and lab smock.  Each student should have in front of them a cake pan, plastic bottle, Dawn in small cup, food coloring, 1/2 cup peroxide, and the dissolved yeast mixture.
    Stand the bottle up in the center of the cake pan. Put the funnel in the opening. Add 3-4 drops of food coloring to the peroxide and pour the peroxide through the funnel into the bottle. Show a water molecule diagram and a peroxide molecule diagram, pointing to the extra oxygen that will be set free in the reaction.
    Add the Dawn detergent to the peroxide in the bottle.
    Pour the yeast mixture into the bottle and quickly remove the funnel.
    The students can touch the bottle to feel any changes that take place.
    How Does It Work?
    Talk about the addition of the yeast as a catalyst, which makes the peroxide molecule release the oxygen atom faster. The teacher who submitted this experiment claims to have done this with hundreds of students from kindergarten through fifth grade and some adults who all loved the experiment. It is very easy and safe to do again at home using regular hydrogen peroxide from the drugstore.
    The reaction creates foam that shoots up out of the bottle and pools in the pan. After a minute or so, it begins to come out in a moving stream that looks like toothpaste being squeezed out of a tube. The students can play with the foam as it is just soap and water with oxygen bubbles. The bottle will feel warm to the touch as this is an exothermic reaction.
  • Chemical Reactions

    1. 1. Chemical Reactions Basic Chemistry i wonder why Physical Science
    2. 2. In your lab notebook, please answer as best you can: 1. What are the horizontal rows of the Periodic Table called? What do the elements in each row have in common? • Elements in each “period” have the same number of occupied energy levels (and some shared chemical and physical properties). 2. What are the vertical columns of the Periodic Table called? What do the elements in each column have in common? • Each “group” of elements has the same number of valence electrons. 3. Which class of elements contains mostly gasses and elements that are dull and brittle? • Nonmetals 4. What group(s) of elements are most likely to donate electrons (become cations)? • Alkali Metals (group 1) and Alkaline Earth Metals (group 2) 4. What chemical properties to the Noble Gasses (group 18 elements) have? • Full valence electron energy levels, very stable/unreactive (inert) Bonus Question: How many elements are liquid at room temperature (72o F)? Can you name them? Review Quiz 5 Two: Mercury (Hg) & Bromine (Br) * Gallium (Ga) and Caesium (Cs) are liquid at 85 degrees Farenheit
    3. 3. Reading The Periodic Table - Review • What is this and what does it tell you? • the atomic number • # of protons (& electrons) • What is this number and what does tell you? • the atomic mass (in amu's) • Average weight of combined protons & neutrons • Calculate the # of neutrons by subtracting the atomic number from the rounded atomic mass • What is this called? • atomic symbol (abbreviation of element name) • allows easier written chemical formulas • H2O2, CO2, C6H12O6 • Describe an electron. • Carries a negative charge. • Very tiny - has virtually no mass. • Orbits around the nucleus in energy levels. Review
    4. 4. Chemical Bonding - Ionic, Covalent, Metallic Review
    5. 5. Electronegativity - how strong an atom tends to pull on other electrons Advanced Topic
    6. 6. Electronegativity • Electronegativity is a measure of how strong an atom tends to pull on electrons of other nearby atoms. • Highly electronegative elements tend to form anions by stealing electrons from atoms with very low electronegativity. Advanced Topic
    7. 7. Chemical Reactions • A chemical reaction occurs when two or more substances interact to form new substances • reactants: the substances that interact in a chemical reaction • products: the new substances formed due to the chemical reaction reactants products • H2 + Cl2 2HCl 2H2 + O2 2H2O reactants product • a diatomic molecule is a molecule made of two atoms hydrogen (g) + chlorine (g) hydrochloric acid (l) hydrogen (g) + oxygen (g) water (l)
    8. 8. Conservation of Mass & Energy • Matter (made of atoms) cannot be created or destroyed. • Law of Conservation of Mass • During chemical reactions, changes will occur, but • No atoms will ever cease to exist • No atoms can ever come from nothing • Atoms can only be rearranged into different forms or substances •Also true for energy •Energy cannot be created or destroyed. • Change forms (see picture) • Move from one place to another
    9. 9. Evidence of a Chemical Change • A chemical change may be indicated by: • A new color forming • Change in temperature (gets warmer or cooler) • Bubbles or precipitate • (evidence that a substance with a different state of matter is forming) • Release of energy • Sound, light, and/or heat Review Also
    10. 10. Experiment 5.2 Reaction Rates (a.k.a. Kool Colors) Observation: • How do you know a reaction is finished? •Name some fast/slow reactions you know about: • FAST: explosions, fire, vinegar/baking soda • SLOW: rusting, photosynthesis, decomposing food, bread rising (yeast) Conclusion: • Did the color change (reaction) happen faster in cold, room temp, or hot Koo-Aid? Why do you think that is? • What patterns do you notice between different groups (different flavors)? • What differences in color change were there between different flavors of Kool-Aid?
    11. 11. Balancing Chemical Equations • What do you notice about reactants & products in this reaction? • Fe + Cl2 = FeCl3 • total # of iron atoms in the reactants: 1 • total # of chlorine atoms in reactants: 2 • To make it equal on both sides, coefficients are added to balance the equation. • 2 Fe + 3 Cl2 = 2 FeCl3 • Let's try another one: • C6H12O6 + O2 = CO2 + H2O ferric chloride Advanced Topic
    12. 12. Steps to Balancing an Equation Step 1 Identify reactants & products and write their chemical formulas on the appropriate sides of the equation. Step 2 Count the number of atoms of each element on each side of the equation. (use a table to keep track) Step 3 Try coefficients that will balance the equation. - Start with elements that appear only once on each side of the equation. - Never change the subscripts in a chemical formula. Step 4 Check to be sure you have the same number of atoms of each element on both sides of the equation. • Example: Balance the equation that takes place when sodium hydroxide reacts with sulfuric acid to form sodium sulfate and water. Advanced Topic
    13. 13. More Practice • Balance the equation that takes place when methane gas reacts with oxygen to form carbon dioxide and water. Step 1: CH4 + O2 CO2 + H2O Step 2: Step 3: CH4 + 2 O2 CO2 + 2 H2O Step 4: Element Before After C 1 1 H 4 2 O 2 3 Element Before After C 1 1 H 4 4 O 4 4
    14. 14. Reaction Rates • Collision Theory: substances cannot react unless their particles come in contact with one another • The more they collide, the more likely they'll react (faster rate) • The slower the particles move, the less likely they'll collide and thus react (slower rate) Factors affecting the rate of reaction: Concentration • More reactants per volume increases the number of particle collisions Temperature • Heat makes particles move faster Surface Area • A spread-out solid increases the chances for liquid or gas to come in contact with it Catalysts • Lower the energy needed to get a reaction started (activation energy) Temperature & Surface Area Demo
    15. 15. Types of Chemical Reactions • Synthesis: two or more substances combine to form a new substance • A + B  AB • examples: photosynthesis, formation of rust and table salt • Decomposition: one substance breaks down into two or more simpler substances • AB  A + B • examples: rotting leaves, electrolysis of water • Combustion: a substance combines with elemental oxygen and produces heat • C 3H8 + 5 O2 3 CO2 + 4 H2O • examples: burning wood, coal or gas, fireworks • Displacement: an atom in a compound is replaced by a different atom • A + BC  B + AC • useful for separating a particular element from a compound • examples: silver from silver nitrate Cu + 2 AgNO3  Cu(NO3)2 + 2 Ag Single Displacement Example Advanced Topic