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Moles & Stoichiometry

Moles & Stoichiometry. By: Skye Smith. What is Mass?. Mass can be defined as a quantitative measure of an object's resistance to the change of its speed. Scientifically speaking, mass IS different than weight, which is the measure of a planet’s gravitational force on an object

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Moles & Stoichiometry

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  1. Moles & Stoichiometry By: Skye Smith

  2. What is Mass? • Mass can be defined as a quantitative measure of an object's resistance to the change of its speed. • Scientifically speaking, mass IS different than weight, which is the measure of a planet’s gravitational force on an object • Mass is ALWAYS CONSERVED. • Scientists use the kilogram (kg) and the gram (g) for units of mass

  3. Atomic Mass • The actual mass of a single atom is ridiculously tiny (on the order of 10^-23 gram) • Using numbers with 10^-23 attached to them all the time would be very inefficient mathmatically • Chemists came up with a scale to put this number into more "real" terms • This is known as the Atomic Mass Unit, or AMU • One AMU=mass of one atom • 1 H atom=1 amu

  4. Avogadro's Number • We still encounter a major problem in the chemistry world however • Chemists don't use "amu's", they use standard units-Kilogram, Liter, Meter...etc. • We need a way to relate amu's and grams • 6.02*10^23 is the magic number • There are 6.02*10^23 atoms in one mole

  5. Molar Mass • The mass in grams of 1 mole of a substance is molar mass • Same thing as gram formula mass, or gfm • With all this information, we can conclude that: • # of moles=grams/gram formula mass • For example the gfm of hydrogen is 1. We are given 3 grams of hydrogen and are asked how much that is in moles. Using the above equation, we conclude that: • # mol=3grams/1amu=3 moles.

  6. What are Moles used for? • You will quickly find out in AP chemistry that moles are used in EVERY problem • The concept of creating balanced chemical equations is almost entirely based on the mole • Without balanced equations, chemists would have a mighty difficult time running reactions because moles determine how much of a substance is needed to properly react in the equation

  7. Balancing Equations • Some basic rules: • The amount of each element on the reactant HAS to equal the amount on the product side • Coefficients are the chemist's best tool for balancing reactions • Note: The coefficients don't affect the mechanism of the reaction • CAN'T change the subscript of the element, changing it will result in an different substance with different chemical properties • Example: H2 + O2 yields H2 O Problem-there are two oxygens on the reactant side and only one on the product side By putting a 2 in front of the hydrogen and the water the equation is balanced 2H2 + O2 yields 2H2 O

  8. Dimensional Analysis • Simply put, dimensional analysis is a tool for solving many unit-related problems. • By using multiplication and division (and correct labeling) chemists can convert moles to coulombs, given the correct information • Here's a simple example: • How many feet are in 3.75 miles? (3.75 miles) x (5,280 feet) = 19,800 feet. 1 1 mile • Since miles is on the top and bottom of the fraction, the unit cancels out, leaving only feet, which is the answer we want.

  9. THE END :)

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