# Essay on Honors Chemistry Semester 1 Exam Review C

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Unit 9: Stoichiometry
Essential questions:
How does the amount of each reactant present at the start of a chemical reaction determine how much product forms? The amount of preactants has to equal the amount of products
How are balanced chemical equations used when solving stoichiometric problems? So the mole ration is correct for the equation
What causes chemical reactions to stop?
What is a limiting reagent ? it is the factor that limits the amount fo product formed from the equation
What is the percent yield of a chemical reaction? The actual yield divided by the theoretical yield multiplied by 100

Key vocabulary: reactant product stoichiometry mole ratio chemical reaction limiting reactant excess reactant theoretical yield actual yield percent yield

Practice:
Differentiate between the significance of the coefficients in a balanced chemical equation and the significance of the subscripts in a chemical formula. Coefficients tell us the number of moles, molecules, or formula units of a species and Subscripts tell us how many atoms or ions there are within a compound
1. State the Law of Conservation of Mass and explain its relationship to stoichiometry. mass is neither created nor destroyed during a chemical relationship.in relationship to stoichiometry it means the mass of the products will always balance out with the reactanst to equal the same mass
2. mole-mole problem:
One disadvantage of burning propane (C3H8) is that carbon dioxide is one of the products. C3H8 + 5O2  3CO2 + 4H2O.
The released CO2 increases the growing concentration of CO2 in the atmosphere. How many moles of carbon dioxide are produced when 10.0 moles of propane are burned in excess oxygen on a gas grill?

n = 30.0 mol CO₂

3. mole-mass problem: Water decomposes to produce hydrogen gas and oxygen gas. How many grams of water would be required to produce 10.0 moles of hydrogen gas? m = 180. g H2O
4. mass-mole problem: If 25.0 grams of carbon dioxide are used in photosynthesis how many moles of glucose (C6H12O6) could be Produced according to the following equation: 6CO2 + 6H2O  C6H12O6 + 6O2 n = 0.0947 mol C₆H₁₂O₆

5. mass-mass problem:
One series of reactions that inflates air bags in automobiles is the decomposition of sodium azide (NaN3). Determine the amount of N2 produced if 100.0 g of NaN3 is decomposed using the following unbalanced equation:
2NaN3  2Na + 3N2 m = 64.64 g N2
6. limiting reactant problem:
Nitrogen gas reacts with hydrogen gas to produce ammonia: ___N2 + ___H2  ___NH3 *not balanced
If 100.0 g of nitrogen gas reacts with 20.0 g of hydrogen gas what mass of ammonia will be produced? m=113 g NH₃
7. Mass to mass and Percent Yield problem: Iron reacts with oxygen to form Iron (III) oxide. 4Fe + 3O2  2Fe2O3.
a) If 200.0 g of iron reacts, what is the theoretical yield of iron (III) oxide? 285.9 g Fe2O3
b) If the actual yield is 205.4 g, what is the percent yield of the reaction? 71.84 % (205.4)/(285.9)X100=71.84% ( 285.9)

Unit 10: States of Matter
Essential questions:
What is the relationship between temperature and kinetic energy? Temperature measures average kinetic energy
How are degrees Celsius converting into Kelvin? Add 273
What are some examples of chemical properties? Physical properties? heat of combustion, reactivity with water, PH, and electromotive force. color, smell, freezing point, boiling point, melting point,
What are some examples of some chemical changes? Burning a log of wood,rusting of metal
How do intermolecular forces determine a substances state? If the intermolecular forces are great enough they can