Second Review Answer Key

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1. Stoichiometry
2. When you balance a reaction that automatically balances the number of atoms on both sides of the equation. Since the number of atoms is the same, the mass must be the same. However, moles do not have to be the same because the substances rearrange and form new substances, thus changing the number of molecules formed. Look at the next question to see how moles and molecules are not conserved once the reactions are balanced.
3. 1. 2 H₂ + O₂ --> 2 H₂O
      
   2. 2 C₂H₂ + 5 O₂ --> 4 CO₂ + 2 H₂O
   3. 3 CaCO₃ + 2 H₃PO₄ --> Ca₃(PO₄)₂ + 3 CO₂ + 3 H₂O
4. 4 Al _(s) + 3 O_{2 (g)} --> 2 Al₂O_{3 (s)}
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   6. 

   States of Matter

5. The kinetic theory says that the tiny particles in all forms of matter are in constant motion. As it applies to gases, there are three assumptions: (also see pp 237-238 in your book)
   1. A gas is composed of particles.
   2. The particles are moving rapidly in constant random motion.
   3. All collisions are perfectly elastic.
6. The amount of kinetic energy in a system is directly related to the Kelvin temperature. At zero K, there is no kinetic energy, hence no molecular motion.
7. The energy being put into the liquid is being absorbed by molecules which now have enough energy to break free of the liquid, thus the temperature does not rise. Also the temperature does not drop because heat is constantly being added.
8. At a temperature of -3 °C and a pressure of 150 kPa,the substance is a solid.
9. Liquids evaporate because some of the molecules on the surface have enough energy to break free of the other liquid molecules and become a gas. Because of the random distribution of kinetic energies and the fact that molecules are constantly colliding and exchanging energy, other molecules will eventually have enough energy and be close enough to the surface to evaporate.
10. 1. K = °C + 273 = 250 °C + 273 = 523 K
    2. x kPa = 45 mm Hg x (101.3 kPa/760 mm Hg) = 6.0 kPa
    3. °C = 4 K - 273 = -269 °C

    Thermochemistry

11. 
    The answer is negative because it is giving off heat (exothermic).
12. 
13. The reaction CaO_(s) + H₂O --> Ca(OH)₂ has a DH value of -65.2 kJ.
    
    1. Exothermic reaction because the DH value is negative.
    2. 
14. Multiply the first equation by 2, including the heat. Add this to the second equation. Add the heats as well. The result is:
    2 Cu_(s)   +   O_{2 (g)}   -->   2 CuO _(s)   DH = -206.6 kJ
    Divide this equation by 2, including the heat, to get the desired reaction. DH = -103.3 kJ
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16. A calorimeter is a device used to measure the amount of heat absorbed or released during a chemical or physical process.
17. 

    Gas Laws

18. See the formulas page.
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22. The pressure inside and outside the building are the same. The temperature inside the building is lower, so the gas molecules slow down and are not bumping into each other as much. In order to keep the pressure constant, the volume will reduce.

    Periodicity

23. A period is a row on the periodic table. A group is a column.
24. a) transition metals - the d block   b) alkali metals - the 1st column   c) halogens - the 2nd to last column   d) noble gases - the last column   e) alkaline earth metals - the 2nd column
25. Reread your text on this section. This will be answered here later as time permits.

    Ionic Bonding

26. An ionic bond is formed by two steps: electrons are completely donated from one atom to another, causing both of the atoms to become ions of opposite charges; these oppositely charged ions then attract to form an ionic bond.
27. 

    Covalent Bonding

28. A covalent bond if formed when 2 electrons are shared between two atoms.
29. 
30. a) tetrahedral - polar   b) linear - nonpolar   c) bent - polar   d) tetrahedral - nonpolar   e) trigonal pyramidal - polar.
31. Van der Waals forces: Dispersion forces are the weakest of the intermolecular forces. They are attractions between molecules, thought to be due to the motion of electrons. Dipole interactions are attractions between polar molecules. The oppositely charged poles are attracted. Hydrogen bonding is a special case of dipole forces. In spite of its name, this is not a bond, it is still an intermolecular attraction. It is the strongest of the three. It occurs when H bonds with a very electronegative element, i.e. F, O, and N, and form very large dipoles (large difference in electronegativity). The attractions between molecules with H-F, H-O, and H-N bonds are stronger than normal dipoles.

    Molarity

32. 
33. 
34. 
    To prepare the solution, dissolve 4.4 g NaCl in 300.0 mL water.
35. M_dV_d=M_cV_c where d = dilute and c = concentrated.First find the amount of 6M HCl needed.
    V_c=(0.40 M x 250.0 mL)/(6 M) = 16.7 mL. Add 16.7 mL of 6 M HCl to 233.3 mL (250.0 - 16.7) water.

    Chemical Equilibria and Kinetics

36. 
37. The four factors that affect reaction rate are: 1. temperature: more kinetic energy to the particles so more chance of collisions and that the collisions will produce a reaction; 2. concentration: more particles available to collide so more probability of reaction; 3. particle size: smaller particle size gives a larger surface area which allows for more chance of collisions; 4: catalyst: increases the rate by providing an alternate path of reaction which has a lower activation energy. The catalyst is not used up in the reaction.
38. The three factors that affect equilibrium are: 1. temperature: if temperature increases,the reaction shifts to relieve the extra heat, so the endothermic reaction is favored. If the temperature is reduced, the opposite is true. 2. concentration: if more of a reactant is added, the reaction shifts (favors products) to use up the excess until equilibrium is reestablished. The same reasoning can be used if a product is added or either are removed. 3. pressure: this only affects gases; if pressure is increased, the reaction shifts to favor the side with fewer gas particles. If pressure is decreased, the reaction shifts to favor the side with more gas particles. See #38 for applications of these.
39. 
40. 2 C₂H₂   +   5 O₂   <-->   4 CO₂   +   2 H₂O +   heat   (though admittedly this is not a very reversible reaction.)
    
    1. If more oxygen is added, the reaction will shift to favor the products.
    2. If CO₂ is removed, the reaction will shift to favor the products.
    3. If pressure is increased, the reaction will shift to favor the products.
    4. If temperature is decreased, the reaction will shift to favor the products.
41. 

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