CHE 17 Name

Test 2

April 18, 1997

Multiple choice: (2 points each)

  1. Which is not true about the ionic compound sodium chloride (NaCl)?
    1. it is electrically neutral.
    2. it was formed when electrons were shared.
    3. it has properties different from the atoms from which it was formed.
    4. it is a white crystalline solid.
  1. When you look at a grain of table salt (sodium chloride), what do you understand composes the crystal?
    1. atoms of sodium and chlorine
    2. molecules of sodium and chlorine
    3. sodium ions and chloride ions
    4. molecules of sodium chloride
  1. Which molecule would be expected to exhibit the least hydrogen bonding?
    1. HF (b) H2O (c) NH3 (d) CH4

4. Chemical equilibrium exists for a chemical reaction when

(a) equal amounts of chemicals exist on reactant and product sides.

(b) one or more of the reactants are used completely.

(c) all molecular activity stops.

(d) reactants are produced as fast as they are consumed.

5. A catalyst speeds up a chemical reaction by

(a) raising the reaction temperature.

(b) providing an alternate reaction pathway.

(c) increasing the concentration of reactants.

(d) none of the above answers are correct.

6. Which of the following samples has the largest entropy?

(a) one mole of liquid water

(b) one mole of solid water (ice)

(c) one mole of gaseous water (water vapor)

(d) Not enough information has been provided to answer this question.

Short answer:

7. Why does putting food in a freezer help to preserve it? Explain in terms of how the involved molecules are affected. (6 points)

 

 

8. Predict the formula for the compound that forms between Ca and Br, explaining your reasoning. (6 points)

 

 

 

9. Name the following compounds. (6 points)

(a) MgSO4

 

(b) Na3PO4

 

10. Which of the following statements about gases is inconsistent with the kinetic molecular theory of matter? Explain. (8 points)

(a) Gases exert more pressure at higher temperatures when the volume is held constant.

(b) Gases will condense at sufficiently low temperatures.

(c) Gases will occupy a larger volume at lower pressures when the temperature remains constant.

 

 

 

 

 

 

 

11. What are the three types of intermolecular forces? In your answer, describe the relative strengths of these forces and explain why all of them are not the same strength. (8 points)

 

 

 

 

 

12. Consider the following equilibrium reaction. How would the following stresses influence the reaction? (9 points)

3 H2 (g) + N2 (g) 2 NH3 (g) + heat

(a) more nitrogen (N2) is added

(b) the reaction mixture is heated up

(c) ammonia (NH3) is removed

Problems:

13. Given the following chemical reaction, how many grams of Al(OH)3 will form when 35 grams of Al4C3 are reacted with excess water? Show your work clearly for full credit. (8 points)

Al4C3 + 12 H2O 4 Al(OH)3 + 3 CH4

 

 

 

 

 

 

 

14. Given the following chemical reaction, how many grams of C3H8 must be reacted to release 1000 kcal of energy? Is this reaction exothermic or endothermic? (9 points)

C3H8 + 5 O2 3 CO2 + 4 H2O + 526 kcal

 

 

 

 

 

 

 

15. For each of the following compounds, write the electron dot structure, predict the molecular geometry, and predict whether the compound will be polar or nonpolar. (4 points each)

(a) AlCl3 (b) CS2 (c) NH4+ (d) PBr3

 

 

 

 

 

 

Essays: Write your answers in complete sentences, using proper grammar. (12 points)

16. We use the term "bond" to describe both covalent bonds and hydrogen bonds. Describe both covalent and hydrogen bonds. Explain how these bonds are different and which one is best described with the term bond.