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Chapter 7.1 Notes

Chapter 7.1 Notes. Describing Reaction. Physical VS Chemical Properties. Physical vs Chemical Properties Physical Change – A change that occurs when some of the properties of a material change, but the substances in the material remain the same.

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Chapter 7.1 Notes

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  1. Chapter 7.1 Notes Describing Reaction

  2. Physical VS Chemical Properties • Physical vs Chemical Properties • Physical Change – A change that occurs when some of the properties of a material change, but the substances in the material remain the same. • Chemical Change – A change that occurs when a substance reacts and forms on or more new substances.

  3. Physical VS Chemical Properties • Signs of a chemical change include color change, temperature change, light produced, gas formed, precipitate formed. • When matter undergoes a chemical change, the composition of the matter changes. When matter undergoes a physical change, the composition of the matter remains the same.

  4. Chemical Reactions • Chemical Reactions • A useful description of a chemical reaction tells you the substances present before and after the reaction. • Reactants – The substances that undergo change and are present before the reaction takes place.

  5. Chemical Reactions • Products – The new substances formed as a result of that change and are present after the reaction takes place. • A chemical equation is a representation of a chemical reaction in which the reactants and products are expressed as formulas. • Reactants  Products

  6. Example 1: Burning Charcoal • Word Equation: Carbon + Oxygen = Carbon Dioxide • Chemical Formula: C + O2 = CO2

  7. Conservation of Mass • Conservation of Mass • The Law of Conservation of Mass states that mass is neither created nor destroyed in a chemical reaction. • Therefore the mass of the products is always equal to the mass of the reactants.

  8. Conservation of Mass • While burning charcoal you actually see the charcoal burn and disappear. The same mass of charcoal that appears to have disappeared is actually converted into carbon dioxide gas.

  9. Balancing Equations • Balancing Equations • In order to show that mass is conserved during a reaction, a chemical equation must be balanced. • Chemical equations can be balanced by changing the coefficients (the numbers that appear before symbols.) • When balancing a chemical equations never change the subscripts in the formula.

  10. E. Steps to Balancing a Chemical Formula • Steps to Balancing a Chemical Formula • Step 1: Count the number of atoms of each element on each side of the equation. • Step 2: change one or more coefficients until the equation is balanced. (Only change the coefficients that need to be changed.)

  11. Ex. 1) Write a balanced equation for the reaction between copper and oxygen to produce copper(II) and oxide, CuO.

  12. Ex. 2) Balance the equation H2O2 H2O + O2

  13. Ex. 3) Balance the equation Mg + HCl H2 + MgCl2

  14. Counting With Moles • Counting With Moles • A mole is an amount of a substance that contains approximately 6.02 X 1023particles of that substance. This number is known as Avogadro’s number • Because chemical reactions often involve large numbers of small particles, chemists use a counting unit called the mole to measure amounts of a substance.

  15. Molar Mass • Molar Mass • Molar mass is the mass of one mole of a substance. • In the same way that a dozen eggs has a different mass than a dozen oranges, a mole of carbon would have a different mass than a mole of sulfur. • The molar mass is the same as the atomic mass expressed in grams

  16. Molar Mass • For a compound you can calculate the molar mass by adding up the atomic masses of its component atoms, and then expressing the sum in grams. Ex. 4) Find the molar mass of a molecule of CO2. • One carbon= 12amu • Two Oxygen= 16amu x 2 = 32amu • 12amu+32amu = 44.0 grams.

  17. Mole-Mass Conversion • Mole – Mass Conversion • Once you know the molar mass of a substance, you can convert moles of that substance into mass, or a mass of that substance into moles.

  18. Ex. 5) Convert 55.0 g of CO2 to moles.

  19. Ex. 6 Convert 144g of H2O to moles

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