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Name __________________________________________Date_______________________Hr_____ HOMEWORK PACKET – CHANGES & BALANCING Chapter 21 Review Questions PART 1 - Use your book to answer the following questions 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. Are atoms made of molecules, or are molecules made of atoms? Which is smaller: the microscopic or the submicroscopic? What is a physical property? What is a chemical property? What doesn't change during a physical change? Why is it sometimes difficult to decide whether an observed change is physical or chemical? What are some of the clues that help us determine whether an observed change is physical or chemical? Is it possible for an element to have more than one atomic formula? How many atoms are in a sulfur molecule that has the elemental formula S 8? What is the difference between an element and a compound? 11. How many atoms are there in one molecule of H3PO4? How many atoms of each element are there in one molecule of H3PO4? 12. Are the physical and chemical properties of a compound necessarily similar to those of the elements from which it is composed? 13. 14. 15. What is the purpose of coefficients in a chemical equation? What do the letters (s), (l), (g), and (aq) stand for in a chemical equation? Why is it important that a chemical equation be balanced? 1 16. 17. 18. Why is it important never to change a subscript in a chemical formula when balancing a chemical equation? Which equations are balanced? Classify the following changes as physical or chemical. Even if you are incorrect in your assessment, you should be able to defend why you chose as you did. a. grape juice turns to wine b. wood burns to ashes c. water begins to boil d. a broken leg mends itself e. grass grows f. an infant gains 10 pounds g. a rock is crushed to powder 19. Is the following transformation representative of a physical change or a chemical change? 20. Each sphere in the diagrams below represents an atom. Joined spheres represent molecules. Explain what’s happening in the picture. 21. 22. 23. What physical and chemical changes occur when a wax candle burns? Which elements are some of the oldest known? What is your evidence? Oxygen atoms are used to make water molecules. Does this mean that oxygen, O 2, and water, H2O, have similar properties? Why do we drown when we breathe in water despite all the oxygen atoms present in this material? PART 2 - Changes in the Properties of Matter: Physical and Chemical 2 What is MATTER? What’s SOLUBILITY? What’s a PROPERTY? Compare and contrast mixtures and solutions. What’s the relationship between elements and atoms? What’s a CHEMICAL CHANGE? List and describe all the PHYSICAL PROPERTIES that are mentioned. What happens in a chemical reaction? What’s the difference between malleability and brittleness? How do you know if a chemical change has occurred? SIGNS What’s a CHEMICAL PROPERTY? Give some examples of chemical changes. Name some chemical property tests. What’s a PHYSICAL CHANGE? When is it hard to tell if something is a mixture? What’s a physical separation? What happens when the rocket takes off in terms of a chemical change? What happens when you run electricity through water? How is digestion a chemical change? Give some examples of confusing physical/chemical changes. What’s a solution? Name some. Explain what happens when something DISSOLVES. 3 PART 3 - Identify each of the following as a Physical or Chemical Change. Put a P next to Physical Changes Put a C next to Chemical Changes 1. A piece of wood burns to form ash. _________ 2. Water evaporates into steam. _________ 3. A piece of cork is cut in half. _________ 4. A bicycle chain rusts. _________ 5. Food is digested in the stomach. _________ 6. Water is absorbed by a paper towel. _________ 7. Hydrochloric Acid reacts with zinc. _________ 8. A piece of an apple rots on the ground._________ 9. A tire is inflated with air. _________ 10. A plant turns sunlight, CO2, and water into sugar and oxygen. _________ 11. Sugar dissolves in water. _________ 12. Eggs turn into an omelet. _________ 13. Milk sours. _________ 14. A popsicle melts. _________ 15. Turning brownie mix into brownies. _________ Choose 2 of the above examples and explain why you chose chemical or physical. Please choose one of each type of change. Back up your explanation. Physical change explanation: _______________________________________________ _______________________________________________________________________ _______________________________________________________________________ _______________________________________________________________________ Chemical change explanation: _______________________________________________ _______________________________________________________________________ _______________________________________________________________________ _______________________________________________________________________ PART 4 – DEALING WITH CHEMICAL EQUATIONS Fill in the blank with the appropriate term(s). chemical change coefficient balanced equation chemical reaction subscript physical property physical change 1. The “3” in CaCO3 ________________________________________ 2. The state, size, or shape of a substance ________________________________________ 3. The “6” in 6H2O________________________________________ 4. What happens when two substances react to produce entirely different substances________________________________________ 4 5. An equation with an equal number of atoms in the reactants and products________________________________________ 6. Ice melting is an example of this kind of change ________________________________________ 7. You cannot create or lose mass in a ________________________________________ PART 5 - Counting Atoms The formula for a compound indicates the elements that make up the compound and the number of atoms of each element present in the compound. These numbers of atoms are indicated by the use of small numbers called subscripts. Sometimes groups of atoms act as a single atom. Such a group of atoms is called a polyatomic ion. If a polyatomic ion is used in a formula more than once, it is put in parentheses and the subscript appears outside of the parentheses. When a subscript appears outside the parentheses, it indicates that all of the elements inside the parentheses should be multiplied by that subscript. For example, the formula Fe(OH) 3 indicates the combination of one atom of iron, Fe, three atoms of oxygen, O, and three atoms of hydrogen, H. In the following examples, list each element in the compound and the number of atoms of each element present. The first example has been done for you. You may already be familiar with some of the compounds. Name Use Formula Calcium carbonate Limestone CaCO3 Aspirin Pain reliever C9H8O4 Magnesium hydroxide Found in milk of magnesia Paradichlorobenzene Moth crystals C6H4Cl2 Acetic acid Found in vinegar C2H4O2 Trinitrotoluene (TNT) Explosive Calcium dihydrogen phosphate Fertilizer Pyrite Fool’s gold Sucrose Sugar Atoms in Formula Ca = calcium =1 C = carbon = 1 O = oxygen =3 Mg(OH)2 C7H5(NO2)3 Ca(H2PO4)2 FeS2 C12H22O11 5 Name Use Formula Sulfuric acid Used in car batteries Cellulose Found in wood products such as your pencil and paper Asbestos Insulator Dichlorodiphenyltrichloroethane (DDT) Banned pesticide Silicon dioxide Sand SiO2 Iron oxide Rust Fe2O3 Butane Lighter fluid C4H10 Atoms in Formula H2SO4 C6H7O2(OH)3 H4Mg3Si2O9 C14H9Cl5 PART 6 – BALANCING EQUATIONS (1) Circle each subscript in each chemical formula. (2) Draw a square around each coefficient. (3) Answer the questions related to each chemical formula. How many atoms of Hydrogen are in this formula as shown? 2 ______ What element does the O represent? ___________________ 1. O 2. CO2 How many atoms of each element are in the formula shown? C = ______ O = ______ 3. 5H2 4. 2C2H6 How many atoms each element are in the formula shown? C = ______ H = ______ 5. 2Na2SO4 How many atoms each element are in the formula shown? Na = ______ S = ______ O = ______ 6 6. H2 What element does the H represent? ___________________ 7. SO4 How many atoms of each element are in the formula shown? S = ______ O = ______ 8. 5C2 How many atoms of carbon are in this formula as shown? ______ 9. 2Fe(OH)3 How many atoms each element are in the formula shown? Fe = ______ O = ______ H= ______ 10. Al(OH)2 How many atoms of each element are in the formula shown? Al = ______ O = ______ H = ______ 7 Part B: Label the chemical equation using PRODUCT, REACTANT, SUBSCRIPT, COEFFICIENT, and YIELDS. 2 Mg + O2 2 MgO Part C: Balance each of the following equations. Remember to count your atoms! 1. H2 2. H2O2 3. Na + O2 H2O H2O + O2 + O2 Na2O 4. N2 + H2 NH3 5. P4 + O2 P4O6 6. C + H2 CH4 7. Al2 O3 Al + O2 8. Fe + H2O 9. C2 H6 10. Na2SO4 + Fe3O4 O2 + CaCl2 + CO2 + CaSO4 NO MORE! H2 H2O + NaCl 8 Atoms are not _______________ or _____________ during a chemical reaction. We know this because of the Law of ____________________________. Scientists know that there must be the ___________ number of atoms on each ___________ of the ____________. To balance the chemical equation, you must add _______________ in front of the chemical formulas in the equation. You cannot _______ or ___________ subscripts! Part A: Identify the following parts of each chemical formula by circling the subscripts and drawing a square around the coefficients. H2 2 HCl 4 O2 CH4 3 CO3 2 NaOH Part B: List the symbols for the atoms in each formula and give the number of each. C2H6 NH3 2MgO 3 Al(OH)3 4P4O10 2 H2O2 Steps: 1) Determine number of atoms for each element. 2) Pick an element that is not equal on both sides of the equation. 3) Add a coefficient in front of the formula with that element and adjust your counts. 4) Continue adding coefficients to get the same number of atoms of each element on each side. For Example: Mg + O2 Mg = MgO O= Mg = Try these: 1. Ca + O2 2. N2 + H2 Ca = N= 3. Cu2O Cu = 4. H2O2 H= O= H= Ca = N= + C H2O + O= O= O= C= H= CaO NH3 Cu Cu = O= H= + CO2 O= C= O2 O= More Balancing Act Practice Continue to balance each equation. Remember you cannot add subscripts or place coefficients in the middle of a chemical formula!!!! 1. Na + MgF2 NaF + Mg 9 2. Mg + HCl MgCl2 + H2 3. Cl2 + KI KCl + I2 4. NaCl Na + Cl2 5. Na + O2 Na2O 6. Na + HCl H2 + NaCl 7. K + Cl2 KCl Challenge: This one is tough! C2H6 + O2 CO2 + H2O 10