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Chemical reactions

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  • 1. Chemical Reactions
  • 2. Recap of Chem vs. Phys Propeties  Chemical Properties- The characteristic of a substance that describes its ability to change into a new substance  Example: Burning of Magnesium into MgO  Physical Properties- A characteristic of a substance that can be observed without changing the substance into a new substance  Example: Ice Melting, Cutting a piece of paper
  • 3. Recap of Chem vs. Phys Changes  Chemical changes- a chemical reaction which results in one or more new substances being formed  Example: Burning a log in a fireplace  Physical changes- a change that alters the form or appearance of something, but does not create a new substance  Example: Melting metal and reshaping into a ring
  • 4. Bonding and Chemical Reactions  In order for a chemical reaction to have taken place, bonds must have been broken and re-created!! Atoms rearrange to create something totally new.  Bonds can change from one form to another; covalently bonded atoms can rearrange to create ionic bonded atoms (like with the Mg lab)
  • 5. Evidence that a Reaction has Occured:        Precipitate forms (solid is formed out of liquids w/o freezing) Heat is released Light is released Energy change (exothermic or endothermic) Gas is formed (usually in the form of bubbles) Color change (unexplained, weird) Rapid temp change (hand warmers, instant ice pack)
  • 6. Balancing Equations Reactant + Reactant  Product + Product In a chemical equation, reactants go on the left, products are always on the right.
  • 7. Conservation of Matter   In 1774, Antoine Lavoisier introduced us to the idea of the conservation of Matter. Conservation of Matter tells us that matter is neither created nor destroyed.   This means that the total mass of the reactants must equal the total mass of products. This also means that the number of atoms stays the same, they are just rearranged when the bonds are broken and re-created.
  • 8. Open vs. Closed    Remember the difference between open and closed systems for a chemical reaction? Open System- the chemical reaction may call upon the elements around it (like taking Oxygen from the air) Closed System- the chemical reaction may only use what it started with and cannot add anything new during the change.
  • 9. Factors of a Chem Reaction  Activation energy- the amount of energy needed to start a chemical reaction (ALL chemical reactions require activation energy)  Surface Area, Concentration, Temperature and presence of catalysts and/or inhibitors will have a huge effect on how quickly a chemical reaction will occur.