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  1. Table of Contents • Observing Chemical Change • Describing Chemical Reactions • Controlling Chemical Reactions • Fire and Fire Safety

  2. - Observing Chemical Change Properties and Changes in Matter • Matter can undergo both physical change and chemical change.

  3. - Observing Chemical Change Energy in Chemical Changes • A student places two substances in a flask and measures the temperature once per minute while the substances react. The student plots the time and temperature data and creates the graph at left.

  4. At 4 minutes the temperature in the flask was about 23ºC. The first time the temperature was 6ºC was at about 7 minutes. Reading Graphs: What was the temperature in the flask at 4 minutes? When was the first time the temperature was at 6ºC? - Observing Chemical Change Energy in Chemical Changes

  5. 20ºC Calculating: How many degrees did the temperature drop between2 minutes and 5 minutes? - Observing Chemical Change Energy in Chemical Changes

  6. The reaction was endothermic; it absorbed thermal energy from the reaction mixture, causing the temperature to drop. Interpreting Data: Is the reaction endothermic or exothermic? Explain. - Observing Chemical Change Energy in Chemical Changes

  7. The reaction stopped at about 2ºC. You can tell because that is the lowest temperature reached. Inferring: At what temperature did the reaction stop? How can you tell? - Observing Chemical Change Energy in Chemical Changes

  8. If the temperature increased, the reaction would be exothermic; an exothermic reaction is one in which energy is released. Drawing Conclusions: Suppose the temperature in the flask increased instead of decreased as the reaction occurred. In terms of energy, what kind of reaction would it be? Explain. - Observing Chemical Change Energy in Chemical Changes

  9. - Observing Chemical Change Asking Questions • Before you read, preview the red headings. In a graphic organizer like the one below, ask a what or how question for each heading. As you read, write answers to your questions. Properties and Changes of Matter Question Answer What are physical properties of matter? Physical properties are characteristics that can be observed without changing one substance into another. What is the evidence for chemical reactions? The evidence for chemical reactions is the formation of new substances and changes in energy.

  10. - Observing Chemical Change Links on Chemical Changes • Click the SciLinks button for links on chemical changes.

  11. End of Section:Observing Chemical Change

  12. Learning Objectives • Apply the principle of the conservation of mass (in other words, balance chemical equations correctly). • Identify what a chemical equation contains (with an example). • Explain what a balanced chemical equation must show. • Identify the 4 main types of chemical reactions.

  13. Synthesis Reaction Experiment • Goals: Observe and write the balanced chemical equations for 2 synthesis reactions, and identify a synthesis reaction. • Procedure: Given verbally. Do NOT touch the penny, tongs, or burner after heating! Only put a pre-1982 penny in the flame! • Results: Observations of the penny after heating (but before you place it in the water) and after placing the penny in the water. • Conclusion: Write the balanced equations for both reactions and describe the characteristics of a synthesis reaction.

  14. - Describing Chemical Reactions Conservation of Mass • The principle of conservation of mass states that in a chemical reaction, the total mass of the reactants must equal the total mass of the products. This is why we must balance chemical equations (because both matter- the number of atoms and mass are conserved)!

  15. Conservation of Mass Review (PSSA Type ?) • For the reaction A + B AB, which masses are equal? • Mass of A = Mass of B • Mass of B = Mass of AB • Mass of A = Mass of AB • Mass of A + Mass of B = Mass of AB

  16. - Observing Chemical Change Properties and Changes in Matter • Chemical reactions occur when bonds break and new bonds form.

  17. - Describing Chemical Reactions Describing Chemical Reactions • Cellular phone messages make use of symbols and abbreviations to express ideas in shorter form. Similarly, chemists often use chemical equations in place of words.

  18. - Describing Chemical Reactions What Are Chemical Equations? • Chemical equations use chemical formulas and other symbols instead of words to summarize a reaction.

  19. - Describing Chemical Reactions Chemical Formulas • The formula of a compound identifies the elements in the compound and the ratios in which their atoms are present.

  20. - Describing Chemical Reactions Balancing Chemical Equations • To describe a reaction accurately, a chemical equation must show the same number of each type of atom on both sides of the equation (due to the principle of the conservation of matter).

  21. Learning Objectives • Apply the principle of the conservation of mass (in other words, balance chemical equations correctly). • Identify what a chemical equation contains (with an example). • Explain what a balanced chemical equation must show. • Identify the 4 main types of chemical reactions.

  22. - Describing Chemical Reactions Balancing Chemical Equations • Magnesium metal (Mg) reacts with oxygen gas (O2), forming magnesium oxide (MgO). To write a balanced equation for this reaction, first write the equation using the formulas of the reactants and products, then count the number of atoms of each element.

  23. Synthesis Reaction Experiment • Goals: Observe and write the balanced chemical equations for 2 synthesis reactions, and identify a synthesis reaction. • Conclusion: Write the balanced equations for both reactions and describe the characteristics of a synthesis reaction.

  24. Synthesis Reaction • Multiple (more than 1) reactantscombining to form 1product. • Example: Copper metal combining with oxygen gas to form copper (II) oxide… • 2Cu + O22CuO

  25. Ratios in Chemical Equations • There’s a 2 to 1 ratio of hydrogen gas (H2) to oxygen gas (O2) that produces 2water molecules. • What’s the ratio of oxygen gas to water? • 1 to 2 + Energy

  26. Balancing Chemical Equations: Balance the equation for the reaction of tin (Sn) with chlorine gas (Cl2), forming tin chloride (SnCl2). - Describing Chemical Reactions Balancing Chemical Equations

  27. Balancing Chemical Equations • Balancing Chemical Equations: • Balance the equation for the reaction of sodium metal (Na) with oxygen gas (O2), forming sodium oxide (Na2O).

  28. Balancing Chemical Equations

  29. PSSA Science Practice • Chemistry • Cells & Heredity • Weather • Physics

  30. What type of change is the melting of ice and WHY? • Chemical; a new substance formed. • Chemical; no new substance formed. • Physical change; no new substance(s) formed. • Physical change; a new substance formed.

  31. Which process involves water vapor forming liquid water? • Condensation • Evaporation • Melting • Dissolving

  32. Which of these substances are elements? • Hydrochloric & carbonic acid • Oxygen and Helium • Carbon dioxide and water • Water and oxygen

  33. At which temperature did a phase change likely take place? • -30oC • -10oC • 0oC • 18oC

  34. A research team wanted to produce a smaller variety of German Shepherd dogs. They mated the smallest dogs from different generations. This is an example of which concept • Extinction • Mutation • Natural Selection • Selective Breeding

  35. Some kinds of fish live in saltwater but lay their eggs in freshwater. Their ability to survive in different environments is an example of • An adaptation • Developmental stages • A habit • Selective breeding

  36. In contrast to multi-cellular organisms, bacteria can undergo major changes in just a few years. This is due to the fact that bacteria • Are microscopic • Do not contain DNA • Reproduce very quickly • Cause infectious diseases

  37. A new variety of tomato is better tasting and can be stored longer than other tomato varieties. This new tomato is produced by placing additional gene segments into the cells of the tomato plant. This process is known as • Genetic Engineering • Selective Breeding • Natural Selection • Sexual Reproduction

  38. Competition is most likely to occur between which 2 organisms? • Deer and butterflies • Owls and bacteria • Goldfish and rabbits • Grass and Strawberry plants

  39. Which statement best describes the energy changes that occur while a child is riding on a sled down a steep, snow-covered hill? • Kinetic energy decreases and potential energy increases. • Kinetic energy increases and potential energy decreases. • Both potential energy and kinetic energy decrease. • Both potential energy and kinetic energy increase.

  40. The effects of natural selection can be seen most quickly in which organisms? • Bacteria • Corn plants • Humans • Cats

  41. Which energy source is renewable? • oil • solar • coal • Natural gas

  42. A television set changes electrical energy to sound and light energy. In this process, some energy is • created • destroyed • Changed to matter • Changed to heat

  43. A spinning pinwheel is held above a lit candle. What energy transformation is taking place? • Heat to mechanical • Mechanical to light • Sound to heat • Heat to sound

  44. Suppose there are 3 satellites near Earth (A, B, & C). A is 5 miles away, B is 15 miles away, and C is 20 miles away. Which satellite would feel the strongest pull from Earth’s gravity? • A • B • C • They would all feel the same pull

  45. The diagram below shows a stationary cart on a frictionless surface. Two unequal opposing forces are about to be applied to the cart. If the unequal opposing forces are applied to the cart at the same time, what will occur? • The cart would move to the left. • The cart would move to the right. • The cart will alternate between moving left and right. • The cart will remain stationary.

  46. Open-ended Question • A student goes skateboarding a few times a week. The student notices that she can go faster while skating on some level surfaces than on others. She hypothesizes that speed has something to do with the surface she is skating on. The student wants to design an experiment to test this hypothesis. a Identify the independent (manipulated) variable in the experiment. [1] ___________________________________________________________ • b Identify the dependent (responding) variable in the experiment. [1] ___________________________________________________________ • c Identify two factors that will need to be held constant in the experiment. [2]    (1)_______________________________________________________ •    (2) ___________________________________________________________

  47. Open-Ended Question • Base your answers to the following questions on the diagram below and on your knowledge of science. The diagram shows two students ready to dive into a pool. • Student A dives from the board into the water. Explain why student A's kinetic energy decreases as the student enters the water. [1]

  48. Which information would probably be most helpful to someone trying to identify a mineral sample? • location and mass of the sample • shape and texture of the sample • hardness and streak of the sample • color and size of the sample

  49. In which type of rock is the fossil imprint of a fern leaf most likely to be found? • Igneous • Metamorphic • Sedimentary • Volcanic

  50. Dust and ash entering the atmosphere as a result of volcanic eruptions can affect  Earth’s • Rotation and revolution • Orbital shape • Tidal activity • Weather and climate