Science 10. Unit 2: Chemistry. Book 3: Chemical Equations & balancing. Block: Name:

Transcription

1 Science 10 Unit 2: Chemistry Book 3: Chemical Equations & balancing Name: Block: 1

2 Chemical vs Physical Change is the science concerned with the properties, composition, and behaviour of matter. is anything that has mass and occupies space. is the amount of matter contained in a thing. Usually the mass of common things is measured in or. are the qualities of a thing, especially those qualities common to a group of things. The relationship between matter and its properties is a very important aspect of chemistry. A p property of a substance is a property that can be found without creating a new substance. For example: A c property is the ability of a substance to undergo chemical change/ and change into a substance. For example: Physical Properties versus Chemical Properties The properties of matter are also classified as being either physical properties or chemical properties. Recall, Physical properties describe, which are changes of or form. Physical properties also describe the physical of a material. Figure The wood that is burning to heat the pot is undergoing chemical changes. The boiling soup in the pot is undergoing a physical change. Chemical properties describe chemical. Chemical changes are those in which a new substance(s) or species is formed (Figure 2.1.2). Chemical properties also describe the tendency of a chemical to. Chemical properties describe relationships or interactions between different forms of matter. They include a chemical s Most physical properties describe relationships or interactions between matter and energy. -Hardness -Malleability -Ductility -Lustre -Viscosity -Diffusion For example, A material can be classified as, or translucent by how it interacts with light. Other physical properties you may have learned about include density,, and surface tension. I Physical properties describe physical changes. Chemical properties describe interactions between different forms of matter...or chemical change. 2

3 Assignment #1: Physical & Chemical Properties Part A & B Complete this assignment in the space provided on the following pages PHYSICAL AND CHEMICAL PROPERTIES AND CHANGES Part A: Physical or Chemical? Identify the following as a chemical (C) or physical property (P): 1. blue color 2. density 3. flammability (burns) 4. solubility (dissolves) 5. reacts with acid 6. supports combustion 7. sour taste 8. melting point 9. reacts with water 10. hardness 11. boiling point 12. shine 13. odor 14. reacts with air Identify the following as chemical (C) or physical (P) changes NaCl (Table Salt) dissolves in water. Ag (Silver) tarnishes. An apple is cut. Heat changes H2O to steam. 5. Baking soda reacts to vineger. 6. Fe (Iron) rusts. 7. Alcohol evaporates. 8. Ice melts. 9. Milk sours. 10. Sugar dissolves in water. 11. Wood rots. 12. Pancakes cook. 13. Grass grows. 14. A tire is inflated. 15. Food is digested. 16. Paper towel absorbs water. 17. An ice cube is placed in the sun. 18. Two chemicals are mixed together and a gas is produced. 19. A bicycle changes colour as it rusts. 20. A solid is crushed into a powder. 21. Two substances are mixed and light is produced. 22. A piece of ice melts and reacts with sodium. 23. Mixing salt and pepper. 24. Chocolate syrup is dissolved in milk. 25. A marshmallow is toasted over a campfire. 26. A marshmallow is cut in half 3

4 Part B Read each scenario. Decide whether a physical or chemical change has occurred and give evidence for your decision. The first one has been done for you to use as an example Scenario Umm! A student removes a loaf of bread hot from the oven. The student cuts a slice off the loaf and spreads butter on it. Your friend decides to toast a piece of bread, but leaves it in the toaster too long. The bread is black and the kitchen if full of smoke. You forgot to dry the bread knife when you washed it and reddish brown spots appeared on it. Physical or Chemical Change? Physical Evidence No change in substances. No unexpected color change, temperature change or gas given off. 4. You blow dry your wet hair In baking biscuits and other quick breads, the baking powder reacts to release carbon dioxide bubbles. The carbon dioxide bubbles cause the dough to rise. You take out your best silver spoons and notice that they are very dull and have some black spots. A straight piece of wire is coiled to form a spring Food color is dropped into water to give it color. Chewing food to break it down into smaller particles represents a change, but the changing of starch into sugars by enzymes in the digestive system represents a change. In a fireworks show, the fireworks explode giving off heat and light. Part C: True (T) or False (F)? 1. Changing the size and shapes of pieces of wood would be a chemical change. 2. In a physical change, the makeup of matter is changed. 3. Evaporation occurs when liquid water changes into a gas. 4. Evaporation is a physical change. 5. Burning wood is a physical change. 6. Combining hydrogen and oxygen to make water is a physical change. 7. Breaking up concrete is a physical change. 8. Sand being washed out to sea from the beach is a chemical change. 9. When ice cream melts, a chemical change occurs. 10. Acid rain damaging a marble statue is a physical change. 4

5 What is a chemical reaction? A is a change that takes place when one or more substances (called -; form one or more substances (called ). reactants products For example: How can you spot a chemical reaction? Chemical reactions can appear very different. As you observe a chemical reaction, you may detect: a change (solid) forming being produced (heat, light) produced (fizzing, bubbles) an being produced. 5

6 A word equation uses the names of the and to show what happens in a chemical reaction. For example, when a piece of sulfur is burned in oxygen gas it produces a white solid called sulfur dioxide. The word equation for this reaction is: A symbol equation uses the of the reactants and products to show what happens in a chemical reaction. (also called a skeleton equation-because it's NOT balanced...yet!)) A symbol equation MUST be to give the correct ratio of reactants and products. This equation shows that atom of sulfur (S) reacts with molecule of oxygen (O 2 ) to make one molecule of sulfur dioxide (SO 2 ). State symbols are added to a symbol equation to show whether the reactants and products are: symbol is (s) symbol is (l) symbol is (g) dissolved in symbol is (aq). With state symbols in place, this symbol equation now shows that the sulfur is a, the oxygen is a and the sulfur dioxide is also a. 6

7 Chemical Reaction Equations Chemical word equations are descriptive but chemical reaction equations are much more efficient. Using chemical symbols and numbers creates a "chemical shorthand" for all chemists to understand... much like txt language saves our thumbs and shortens convs. The general form of a chemical equation is: Sodium metal reacts with chlorine gas to produce sodium chloride crystals. Chemical Word Equation: Skeleton chemical reaction equation: Balanced chemical reaction equation: Quick Check 1. Convert the following from a word equation to a formula equation: Calcium oxide powder is combined with water to form calcium hydroxide solid. 2. Convert the following from a formula equation to a word equation: H2CO3(aq) CO2(g) + H2O(l) 7

8 Assignment # 2: Writing Word Equations pg 8-9 Complete this assignment in the space provided on the following pages 8

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10 Law of Conservation of Mass Figure 4.30 The hydrogen and oxygen in the balloon do not react until the balloon is touched by a flame (A). Then, an explosive chemical B reaction occurs (B). What happens to atoms of hydrogen and atoms of oxygen when the two gases are brought together and ignited? Are new atoms created in the flash? Are some destroyed? 2H 2 (g) O 2 (g) 2H 2 O(g) Figure 4.32 The reaction of oxygen molecules with hydrogen molecules involves rearranging atoms in new ways. When a chemical reaction occurs, new compounds are created, BUT No new matter is created or destroyed; atoms are just as the atoms change partners to form new compounds. If there are atoms of oxygen in the reactants, THERE MUST BE atoms of oxygen in the products. Number of each a in reactants = number of each a in products. This is called THE LAW OF CONSERVATION OF ATOMS. And also explains why we must balance chemical equations. THE LAW OF CONSERVATION OF MASS The law of conservation of mass states that mass is conserved in a chemical reaction. The of the products is always equal to the of the reactants in a chemical reaction. The idea that atoms are (neither made nor destroyed) is believed to be true for all chemical reactions. 10

11 Balancing Chemical Equations A brief examination of the equation for the decomposition of mercury(ii) oxide, HgO (s) --> Hg (l) + O 2(g), shows that it does not obey the law of conservation of mass. The reactant, HgO contains oxygen atom than the products, Hg and O 2. To show that the mass before and after a chemical reaction occurs remains constant, the formula equation has to be. Balancing a chemical equation requires the placement of coefficients in front of reactant and/or product species. Hg O Hg O O are numbers that multiply the entire chemical species that follows them. Figure The reactant in this reaction weighs less than the products. These numbers ensure that the number of on the reactant side is equal to those on the product side of the equation. It is critical to remember balancing must always involve the placement of coefficients and NEVER the changing of subscripts. Altering the subscripts will give an incorrect formula for a substance. Example Balance (NH 4) 3PO 4 + NaOH Na 3PO 4 + NH 3 + H 2O The Method Note: Until you are finished balancing, missing coefficients are treated as zeros!** Do not start with atoms that are easy or difficult to balance; it s best to balance them last. Elemental species are easy; elements that occur in more than one species on each side (usually O and H) are tough! Balance preserved groups (those that don t come apart) whenever possible. Find an element that only occurs in one species on each side; these are usually metal ions. Put a coefficient in front of the two species so as to balance the element of interest. (** Very Important: The 1 st step is the only step where you place coefficients on both sides.**) (NH 4) 3PO 4 + NaOH Na 3PO 4 + NH 3 + H 2O You have successfully balanced one element. Booyah! The problem has now becomes easier to solve. The coefficients will also have fixed another element (or group) on one side. Now place a coefficient to balance the atom (or group) on the opposite side. (NH 4) 3PO 4 + NaOH Na 3PO 4 + NH 3 + H 2O Repeat the process until all of the elements are balanced. (NH 4) 3PO 4 + NaOH Na 3PO 4 + NH 3 + H 2O (NH 4) 3PO 4 + NaOH Na 3PO 4 + NH 3 + H 2O Omit coefficients of 1 in your final answer. **Always do a check to make sure that all atoms are balanced.** (NH 4) 3PO 4 + NaOH Na 3PO 4 + NH 3 + H 2O 11

12 Example 1 Balance K + H 2O KOH + H 2 Example 2 Balance MoCl 3 + O 2 + AgCl MoCl 4 + Ag 2O 12

13 Assignment #3: Balancing Equations Review pg Complete this assignment in the space provided on the following pages 13

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15 Writing and balancing equations Skills: Interpreting, Numeracy, Knowledge 1 Define the Law of Conservation of Mass. 2 Apply the Law of Conservation of Mass by balancing the following equations. a CH 4 (g > + 0 2<g ) - C0 2 < g > + H 20 cn b Klcaq) KN 03( aqj C Hl04(aq) + KOH (a ql + d Ales> + A1Cl 3 < > e NH 3 <g> + + You must apply the following steps to write balanced chemical equations. Write the word equation for the reaction. Directly underneath the word equation, write the unbalanced formula equation. Add subscripts-(s), (1), (g) or (aq). Balance the equation. Note: Dilute means a solution with water and therefore the appropriate subscript is (aq). The table below lists various compounds and the chemical formula of each compound. Compound name Compound formula Compound name Compound formula Hydrochloric acid HCI Nitric acid HN0 3 Sulfuric acid H 2 S0 4 Magnesium chloride MgCl 2 Barium sulfate BaS0 4 Sodium sulfate N3iS0 4 Water H 2 0 Carbon dioxide Calcium carbonate Calcium nitrate Magnesium hydroxide Barium nitrate Sodium hydroxide Sodium carbonate CO 2 CaC0 3 Ca(N0 3 ) 2 Mg(OH) 2 Ba(N0 3 ) 2 NaOH N3iC0 3 Science Focus 4 Homework Book 3 15

16 Chemical e uations page 2 Writing and balancing equations Skills: Interpreting, Numeracy, Knowledge 3 Use the information in the table on page 1 of this worksheet to construct balanced chemical equations, including subscripts, for each of the following reactions. a Dilute hydrochloric acid is added to solid magnesium hydroxide, producing water and the soluble salt magnesium chloride. b Dilute nitric acid is added to solid calcium carbonate, producing bubbles of carbon dioxide, water, and the soluble salt calcium nitrate. c When dilute sodium sulfate solution is added to dilute barium nitrate solution, barium sulfate precipitates, leaving sodium nitrate in solution. d Dilute sodium hydroxide is added to dilute sulfuric acid, producing water and the soluble salt sodium sulfate. e Dilute sulfuric acid is poured over solid sodium carbonate, producing carbon dioxide, water and the soluble salt sodium sulfate. 4 Construct balanced equations, including subscripts, for the following reactions. You may need to use the cross method from Worksheet 1.1 to construct the chemical formulas first on a separate sheet of paper. a Iron metal reacts with chlorine gas to produce iron chloride. b Sodium chloride solution is mixed with silver nitrate solution, producing a precipitate of solid silver chloride. c Lead nitrate solution is added to sodium sulfate solution, producing lead sulfate precipitate. d Sulfur dioxide gas reacts with oxygen to produce sulfur trioxide gas. 16