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Unit 5 Part 1 - Chemical Change
 

Unit 5 Part 1 - Chemical Change

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    Unit 5 Part 1 - Chemical Change Unit 5 Part 1 - Chemical Change Presentation Transcript

    • Chemical Reactions
    • Part 1 Chemistry and Change…
    • Review
      • Chemists classify the changes that they observe in substance into two broad categories:
        • Physical
        • Chemical
      • When water as a liquid changes to steam, is there a Chemical change?
    • Is there a chemical change here?
      • Can you reverse the change made to the tomato? Chemical Reaction A chemical change is also known as a chemical reaction
      • Chemical reaction – is a process by which one or more substances undergo chemical changes into one or more different substances
        • “ Process” – this means it takes time.
        • “ one or more substances”
        • “ new” – different from what you started with.
    • Law of Conservation of Mass
      • Law of Conservation of Mass “Mass is neither created nor destroyed during a chemical reaction”
        • 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.
      • 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.
      • Ex: Two H 2 molecules and one O 2 make 2 water molecules.
    • Chemical Equations
      • Chemical Equations are how chemists represent a chemical reaction.
      • Chemical Equations: Indicate the substances “reacting” (changing) during the reaction.
        • Indicate chemicals which affect the time for the reaction to occur (catalysts).
        • Indicate the new substances formed following the reaction.
    • Writing Chemical Equations
      • There are three ways to indicate chemical reactions. 1. Word Equation 2. Skeleton Equation 3. Balanced Chemical Equation (Preferred)
    • Things you will find in a chemical equation.
      • Reactant(s) – the starting substances.
      • Product(s) – the new substances formed by the reaction.
      • Values – indicating the amount of substances (like a recipe). Symbols, to divide the reactants from the products and tell chemists the state of substances
    • Word Equations
      • 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.”
    • Writing Word Equations
      • Write a word equation for the following chemical reactions:
        • Water under electrolysis produces hydrogen gas and oxygen gas.
        • Solid Sodium and chlorine gas will combine to yield sodium chloride.
      • Word equations are too long to write and do not give enough information about the substances in the reaction. Typically they are not used.
    • Skeleton Equations
      • Instead of writing words, skeleton equations use chemical formulas.
      • Writing a Skeleton Equations
        • Write skeleton equations for the two examples above.
        • Note: remember diatomic molecules?
      • Skeleton equations are an improvement over word equations, but do not satisfy the law of conservation of mass.
    • Balanced Chemical Equations
        • Similar to skeleton equations, but satisfy the Law of Conservation of Mass.
      • Balancing a Chemical Equation
    •  
    • Write Balanced Chemical equations for the skeleton equations above: