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Chemical Reactions

Chemical Reactions. Evidence of a Chemical Reaction. Chemical Change - vs - Physical Change. http://www.youtube.com/watch?v=MTFOxR2cg0g&feature=related&safety_mode=true&persist_safety_mode=1&safe=active. Physical Change.

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Chemical Reactions

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  1. Chemical Reactions Evidence of a Chemical Reaction

  2. Chemical Change -vs- Physical Change http://www.youtube.com/watch?v=MTFOxR2cg0g&feature=related&safety_mode=true&persist_safety_mode=1&safe=active

  3. Physical Change • Physical change: a change that occurs that does not change the identity of the substance • Melting ice • Freezing Kool-Aid • Tearing paper • Boiling water

  4. Chemical Changes • Chemical change: a change that occurs causing the identity of the substance to change • Burning • Digesting food • Reacting with other substances • A chemical change is called a chemical reaction

  5. Chemical reactions • A chemical reaction involves changing the ways the atoms are grouped. H2 + Cl2   -->   2 HCl2 H2 + O2   -->   2H2O

  6. Chemical Reaction • A process in which one or more substances, the reactants, are converted to one or more different substances, the products. • A chemical reaction rearranges the atoms of the reactants to create different substances as products

  7. How do we know a chemical reaction has occurred? http://www.youtube.com/watch?v=cZMkqagL8Ps&safety_mode=true&persist_safety_mode=1&safe=active

  8. Evidence for a Chemical Reaction • Precipitation • A solid formed from a solution can result from a chemical change.

  9. Evidence for a Chemical Reaction • Gas Production • Fizzing, bubbling • Color Changes • Odor Changes

  10. Evidence for a Chemical Reaction • Energy Changes • Exothermic • Heat is released (feels hot) • Endothermic • Heat is absorbed (feels cold) • Light can be absorbed or released also without a temperature change.

  11. Steps for predicting precipitates • Step 1 – Write the reactants as they actually exist before any reaction occurs. • Step 2 – Consider the various solids that could form. • Step 3 – Use the solubility rules to decide whether a solid forms, and, if so, to predict the identity of the solid.

  12. Soluble Solid • Solid that readily dissolves in water. • Insoluble solid and slightly soluble solid • Very small amount dissolves in water, the majority stays solid.

  13. Chemical Equation • A representation of a chemical reaction showing the relative numbers of reactants and products. ReactantsProducts “Yields”

  14. Parts of a chemical Equation

  15. Subscripts vs. Coefficients • The subscripts tell you how many atoms of a particular element are in a compound. • The coefficient tells you about the quantity, or number, of molecules of the compound.

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