Unit 5 Part 1 - Chemical Change


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Unit 5 Part 1 - Chemical Change

  1. 1. Chemical Reactions
  2. 2. Part 1 Chemistry and Change…
  3. 3. Review <ul><li>Chemists classify the changes that they observe in substance into two broad categories: </li></ul><ul><ul><li>Physical </li></ul></ul><ul><ul><li>Chemical </li></ul></ul><ul><li>When water as a liquid changes to steam, is there a Chemical change? </li></ul>
  4. 4. Is there a chemical change here? <ul><li>Can you reverse the change made to the tomato? Chemical Reaction A chemical change is also known as a chemical reaction </li></ul><ul><li>Chemical reaction – is a process by which one or more substances undergo chemical changes into one or more different substances </li></ul><ul><ul><li>“ Process” – this means it takes time. </li></ul></ul><ul><ul><li>“ one or more substances” </li></ul></ul><ul><ul><li>“ new” – different from what you started with. </li></ul></ul>
  5. 5. Law of Conservation of Mass <ul><li>Law of Conservation of Mass “Mass is neither created nor destroyed during a chemical reaction” </li></ul><ul><ul><li>I.e. If you started with 10kg of substances at the beginning of the reaction, you will end with 10kg of new substances at the end. </li></ul></ul><ul><li>A toms rarely, if ever, change into other elements during most chemical changes. Therefore the atoms of each element we started with will be present at the end of the reaction. </li></ul>
  6. 6. <ul><li>Ex: Two H 2 molecules and one O 2 make 2 water molecules. </li></ul>
  7. 7. Chemical Equations <ul><li>Chemical Equations are how chemists represent a chemical reaction. </li></ul><ul><li>Chemical Equations: Indicate the substances “reacting” (changing) during the reaction. </li></ul><ul><ul><li>Indicate chemicals which affect the time for the reaction to occur (catalysts). </li></ul></ul><ul><ul><li>Indicate the new substances formed following the reaction. </li></ul></ul>
  8. 8. Writing Chemical Equations <ul><li>There are three ways to indicate chemical reactions. 1. Word Equation 2. Skeleton Equation 3. Balanced Chemical Equation (Preferred) </li></ul>
  9. 9. Things you will find in a chemical equation. <ul><li>Reactant(s) – the starting substances. </li></ul><ul><li>Product(s) – the new substances formed by the reaction. </li></ul><ul><li>Values – indicating the amount of substances (like a recipe). Symbols, to divide the reactants from the products and tell chemists the state of substances </li></ul>
  10. 10. Word Equations <ul><li>The least descriptive way to explain a chemical reaction. Iron(s) + Chlorine(g)  iron (III) chloride In sentence form it reads: “solid iron when combined with gaseous chlorine produces iron (III) chloride.” </li></ul>
  11. 11. Writing Word Equations <ul><li>Write a word equation for the following chemical reactions: </li></ul><ul><ul><li>Water under electrolysis produces hydrogen gas and oxygen gas. </li></ul></ul><ul><ul><li>Solid Sodium and chlorine gas will combine to yield sodium chloride. </li></ul></ul><ul><li>Word equations are too long to write and do not give enough information about the substances in the reaction. Typically they are not used. </li></ul>
  12. 12. Skeleton Equations <ul><li>Instead of writing words, skeleton equations use chemical formulas. </li></ul><ul><li>Writing a Skeleton Equations </li></ul><ul><ul><li>Write skeleton equations for the two examples above. </li></ul></ul><ul><ul><li>Note: remember diatomic molecules? </li></ul></ul><ul><li>Skeleton equations are an improvement over word equations, but do not satisfy the law of conservation of mass. </li></ul>
  13. 13. Balanced Chemical Equations <ul><ul><li>Similar to skeleton equations, but satisfy the Law of Conservation of Mass. </li></ul></ul><ul><li>Balancing a Chemical Equation </li></ul>
  14. 15. Write Balanced Chemical equations for the skeleton equations above: