Chem Review

4686 Words Dec 23rd, 2012 19 Pages
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Unit 9: Stoichiometry
Practice
1. Differentiate between the significance of the coefficients in a balanced chemical equation and the significance of the subscripts in a chemical formula.
· Coefficients show the correct proportions of atoms and molecules in a chemical reaction. They are normal sized numbers placed at the beginning of the chemical formulas in a chemical reaction during the process of balancing. They tell how many of an entire chemical formula is in a reaction.
· Subscripts show the correct proportions of atoms/ions in a chemical formula. They are the small numbers within the chemical formula. They tell how many individual atoms/ions are present.
2. State the Law
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7. What is plasma?
· Plasma has neither a definite volume nor a definite shape.
· Plasma is often seen within ionized gases.
· Plasma is distinct from a gas because it possesses unique properties: o It contains free electrical charges (not bound to atoms or ions) o It can be produced by heating and ionizing a gas. · Plasma is often found in areas of the planet/universe where extremely high heats are possible and gases exist to help create the plasma.
8. Put hydrogen bonds, dispersion forces and dipole-dipole forces in order of how strong they are and give an example of each type of attraction.
· Strongest = Hydrogen bonds which have hydrogen attached to a fluorine, oxygen, or nitrogen (Example: Oxygen’s attraction to other hydrogens in a bunch of H2O’s)
· Medium Strength = Dipole-Dipole bonds which occur between the slight positive end of one polar molecule and the slight negative end of another polar molecule (Example: Nitrogen’s attraction to other hydrogens in a bunch of NH3’s)
· Weakest = Dispersion forces which occur in any covalently bonded molecule (Example: Hydrogen’s attraction to other hydrogens in a bunch of CH4’s) Ø Note 1: These are intermolecular forces of attraction so they occur OUTSIDE of the molecules! Ø Notes 2: One covalent bond can be all three types at once.
9. Why do polar compounds tend to have higher melting boiling points than nonpolar compounds? Polar compounds have electrostatic

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