1. Use the Equation That Follows to Answer the Questions Below

CHM 101 NAME______GAGE FALL 2005 October 28, 2005 EXAM 2

1. Use the equation that follows to answer the questions below.

2 C3H8O3 + 7 O2 ------> 8 H2O + 6 CO2

a. How many moles of oxygen are needed to react with 4.55 x 10-2 moles of glycerin?

b How many grams of water are formed from the reaction of 3.08 moles of glycerin?

c. How many grams of water will form from the reaction of 35.0 grams of glycerin and 45.0 grams of oxygen? (11)

d. Suppose you started with 15.0 grams of glycerin and formed 11.4 grams of water. What is your % yield? (8)

1 2. a. You take a solid and dissolve it in water while making a variety of observations. You discover that the process is endothermic. Explain how you know this based on possible observations. (5)

b. Use the energy-reaction progress diagram on the last page to answer the questions that follow.

Label a point that is all reactants with R and one that is all products as P. (2)

What is activation energy? What is the value for the activation energy for this reaction? (3)

Is the reaction endothermic or exothermic? ______(1)

What is ∆H for this reaction? ______(2)

3. Bohr decided that the electrons surrounding an atomic nucleus are arranged in energy levels like planets orbiting the Sun. The quantum mechanical model retains this idea of electron energy levels. Explain what is different about the quantum mechanical model and what evidence is used to justify it. (5)

2 4. a. Write the Lewis dot structure for each of the substances below. (8)

1- CH3Br COCl2 SrS SeCl5

b. For any covalent molecules in (a), draw a structural formula and show all bond dipoles. Indicate whether each bond is polar or non-polar. (8)

c. Which of the following species will show resonance? Justify your answer. (4)

2- SO3 SO2

d. You can write two different dot structures for carbon disulfide as shown below. Which one is preferred and why? (4)

:::S:C:::S: ::S::C::S::

3 5. Place the following sets of substances in order from lowest to highest value for the property listed and explain the reason for that order. (12)

a. electronegativity

P O Na Si ______

b. first ionization energy

Mg S Si Se ______

c. ionic radius

Ca2+ Al3+ S2- Cl1- ______

6. Supply the information for each item below. (18)

a. full electron configuration for selenium ______

b. -35oC in kelvins ______

c. mathematical equation relating ______frequency and wavelength d. element with last electron added as 4p2 ______

e. example of a compound that contains both ______ionic and covalent bonding f. simple atom diagram for copper

4 Reaction Progress

400 ) J k ( y

g 300 Series1 r e n E

0 0 5 10 15 20 25 Time (sec)