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Chemical & Physical Change Review


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Chemical & Physical Change Review

  2. 2. Properties of Matter  Brittleness - the property of matter that is how easily the substance breaks or shatters when force is applied to it.  Ductility - property of a metal in which it can be stretched without breaking.  Elasticity - the ability of a substance to be stretched and then to return to its original shape.  Hardness - property of matter that determines how easily the substance can be scratched.  Malleability - the property of a metal that allows it to be hammered, rolled, pressed or forged.
  4. 4. HOW DOES ONE STUDY FOR A LAB?  Practice with the tools, e.g. thermometer, scales, weighing tray, stopwatch, calculators  Practice making graphs, especially line graphs (x: time, y: temperature), using data tables  Memorize the definitions of key science words  Use other sources for quizzing, e.g. BrainPop,  Make own quiz/test  Have a peer/parent quiz you on definitions/method
  5. 5. KEY WORDS: CHEMICAL CHANGE  Chemical change  Endothermic reaction  Exothermic reaction
  6. 6. CHALLENGE Is cooking an example of chemical or physical change?
  7. 7. Cooking  When most of the food is cooked, it can not be reversed to the original substance it was in before cooking it, for example, when meat is cooked it changes the color.
  8. 8. chemical change  A chemical reaction is a chemical change which forms new substances; the starting materials (reactants) are different from the product  When a chemical change takes place there is the change of temperatures where there might be loss of heat but in most chemical change reactions heat or energy is produced.  Another characteristic of a chemical change is the change in color. For example when an iron nail comes into contact with water, the nail begins to rust and its color change from silver to reddish brown meaning that chemical change has taken place.  The production of gases and solids is also another characteristic of a chemical change.The gases produced appear in the form of bubbles as a result of the reaction. A solid maybe formed and it separates itself from the solution after the reaction.
  9. 9. BrainPop Movie  opertychanges/preview.weml
  10. 10. Endothermic reaction  An endothermic reaction is any chemical reaction that absorbs heat from its environment. It is a reaction that requires energy to proceed.The intake of energy may be observed as a decrease in temperature as the reaction proceeds. Once the reaction is complete, the temperature of the mixture will return to room temperature.  Examples 1. 2. reacting ethanoic acid with sodium carbonate 3. photosynthesis (chlorophyll is used to react carbon dioxide plus water plus energy to make glucose and oxygen)
  11. 11. Exothermic reaction  Many chemical reactions release energy in the form of heat, light, or sound.These are exothermic reactions.  Exothermic chemical reactions produce heat.  Examples 1. In this reaction vinegar is used to remove the protective coating from steel wool, allowing it to rust.When the iron combines with oxygen, heat is released.
  12. 12. Collecting Data Endothermic Exothermic InitialTemperature °C °C FinalTemperature °C °C Temperature change rate
  13. 13. Graphing rate of reaction
  14. 14. Law of Conservation of Mass CHALLENGE: EXPLAIN WITH EXAMPLE
  15. 15. Law of Conservation of Mass  the mass of substances produced (products) by a chemical reaction is always equal to the mass of the reacting substances (reactants).  in a chemical reaction, the mass of the products equals the mass of the reactants.  Example 1.00g carbon + 5.34g sulphur 6.34g carbon disulphide
  17. 17. How do I study for a Science quiz?
  18. 18. Types of Science Questions KNOWLEDGE What is the freezing point of water? COMPREHENSION Explain the difference between physical and chemical change? ANALYSIS Which is a physical change and why? Sugar dissolved in water Burning paper turning into ash SYNTHESIS In cold countries salt is strewn on icy roads. Explain the scientific reason ing behind this.
  19. 19. Key words: Physical Change  Boiling point  Melting point  Sublimation  Deposition  Solidification or Freezing  Evaporation  Filtration (separation technique)  Solution = Solute + Solvent
  20. 20. What is a physical change? Give a real life example of a physical change?
  21. 21. Requires energy from environment Cooling Process Releases energy to environment Warming Process
  22. 22. Changes in States of Matter Deposition Evaporation Solidification/Freezing Melting Sublimation Condensation
  23. 23. Temperature(degreesCelsius) Time (minutes) 0 100 Time-Temperature Graph for Water Why is the slope of the graph flat (no temperature change) at 0 degrees? Why is the slope of the graph flat (no temperature change) at 100 degrees even though the stove is still on? What is true for the ice-water mixture when the temperature began to rise? Why did temperature increase at a constant rate? When will the temperature of the water rise above 100 degreesCelsius?
  24. 24. Temperature(degreesCelsius) Time (minutes) 0 100 Time-Temperature Graph for Water As the temp approaches melting point temperature, the KE of the water molecules increases loosening the bonds between water molecules. As the ice begins to melt, additional heat energy does not raise the temperature of the water, but loosens the bonds changing ice to water. i.e. phase change – melting. Once the water is in a liquid phase, increasing the amount of heat input raises the temp of the liquid water. As the temp approaches boiling point, the KE of the molecules is sufficient to allow the separation of molecules into the gas phase. As the liquid begins to boil. Additional input of heat energy does not raise the temperature of the water, rather it is used to break water bonds. i.e. phase change. Once the water is in the gas phase, additional heat input raises the temperature of the water vapor Note: greater energy is needed to vaporize water than to melt it.WHY?
  25. 25. Phase Change- _________ energy from stove = energy required for phase change ____ temperature change Phase Change- ___________ energy from stove = energy required for phase change ______ temperature change Energy from stove causes increased ____E and increased ___________ Energy from stove causes increased ___E and increased _____________ ______ states of Matter ______ states of Matter _____ states of Matter
  26. 26. Phase Change- Melting energy from stove = energy required for phase change No temperature change Phase Change-Vaporization energy from stove = energy required for phase change No temperature change Energy from stove causes increased KE and increasedTemperature Energy from stove causes increased KE and increasedTemperature Two states of Matter Two states of Matter One states of Matter
  27. 27. The Water Profile
  28. 28. Boiling point  temperature at which a liquid changes to a gas
  29. 29. Melting point  the temperature at which a substance changes from a solid to a liquid.
  30. 30. Solidification (freezing)  changing of a liquid to a solid
  31. 31. Salt on snow-covered roads?  If you live in an area with a cold and icy winter, you have probably experienced salt on sidewalks and roads, used to melt the ice and snow and keep it from refreezing.  Salt is also used to make homemade ice cream.  In both cases, the salt works by lowering the melting or freezing point of water.The effect is termed 'freezing point depression'. ”  So, when you add a salt to ice with a little bit of water, the salt lowers the freezing point of the water, keeping it from re- freezing as easily and helping to melt the rest of the ice.
  32. 32. Sublimation  the changing of a solid directly to a gas  Example Dry ice is solid carbon dioxide. At room temperature and pressure, it sublimates into carbon dioxide vapor.
  33. 33. Deposition  this is a phase change from a gas directly to a solid Iodine test: Dry Ice The Iodine Test
  34. 34. Evaporation  changing of a liquid to a vapor at any temperature below its boiling point.
  35. 35. Alcohol Water Oil NATURE OFTHE SUBSTANCE Why does alcohol evaporate faster?
  36. 36. 2. Copy and complete the following sentences using the words below: Solution solvent solute saliva dissolves exposed saliva The candy dissolves in the …………………… your mouth to form a liquid ………………………….. Solutions contain two parts, a ………………….. and a ………………………………. The solvent is …………………….. and the solute is the candy. The solute……………………….. by spreading out evenly throughout the solvent. The candy can quickly dissolve when it is ……………… to chewing and stirred by moving it around with the tongue.
  37. 37. Pressure CookerVisualizer
  38. 38. Ms Pommeroy cooks rice in a pressure cooker. Why?  A pressure cooker is a sealed pot.  Steam trapped inside the pot under pressure allows the temperature to rise beyond what it could reach normally in a traditional uncovered pot.  As the pressure inside the cooker increases, the boiling point of the water inside increases as well.This causes the food to cook at a higher temperature, which cooks it faster.
  39. 39. CHEMICAL CHANGE PHYSICAL CHANGE In a chemical change where there is a chemical reaction, a new substance is formed and energy is either given off or absorbed. A physical change in a substance doesn't change what the substance is. If a piece of paper is burned, it is broken up into different substances that are not paper. For example, if a piece of paper is cut up into small pieces it still is paper.This would be a physical change in the shape and size of the paper. Chemical changes cannot be reversed with the substance changed back without extraordinary means, if at all. Physical changes can be reversed. If one made a recipe for a cake with flour, water, sugar and other ingredients and baked them together, it would take extraordinary means to separate the various ingredients out to their original form. If one decided to mix sugar/salt into water to make sugar/salty water, this would be a physical change as the water could be left out to evaporate and the sugar/salt crystals would remain. Note: remember salt is sodium chloride (NaCl)
  40. 40. GOOD LUCK!