3SAS #31-38, page 235 & 3SBS #1-10, page 258

3SAS #31-38, page 235

31) Name and give the molecular formula for the alkane with a molar mass of
a. 44 g/mol
b. 72 g/mol

a. Propane, C3H8
b. Pentane, C5H12

32) What does -ane imlply about the carbon-carbon bonding in hexane?

The suffix -ane implies that hexane is an alkane.

33) Are the following three molecules isomers of one another? Explain your answer. [diagram]

Yes, each of these molecules are isomers of one another. They are all combosed of 5 carbon atoms and 12 hydrogen atoms, but appear to be different because of the arrangement of atoms. These three molecules are structional isomers of one another, for they have identical molecular formulas but different arrangements of atoms.

34) Draw structural formulas for at least three structural isomers of C9H20

See drawings.

35) What is the shortest-chain alkane that can demonstrate isomerism?

Butane (C4H10) is the shortest-chain alkane that can demonstrate isomerism- alkanes with four or more carbon atoms can be demostrated as straight-cchain structures, branched-chain structures, and ring structures.

36) An unbranched hydrocarbon molecule can be represented as a linear chain or as a zig-zag chain. Explain in what way both representations are correct.

Both representations are correct because their different arrangements of atoms does not change the identical molecular formulas of the molecule; this would make the molecules structural isomers of each other.

37)
a. Draw two hexane structural isomers, one a straight-chain molecule and the other a branched-chain molecule.
b. Which of the two isomers you drew would have the lower boiling point? Explain your answer.

a. See drawing.
b. The branched-chain molecule would have the lower boiling point. Since the straight-chain molecule has greater molecule-to-molecule contact, it has a stronger intermolecular force than the branched-chain molecule, resulting in a higher boiling point.

38) Which of each pair of the following hydrocarbon molecules would have the lower boiling point? In each case, describe your reasoning.
a. a short, straight chain or a long, straight chain.
b. a short, branched chain or a long, branched chain.
c. a short, branched chain or a long, straight chain.

a. A short, straight chain would have a lower boiling point because of decreased molecule-to-molecule contact than the longer boiling point. The bonds of this chain would be easier to break than a longer straight chain. However, this straight chain would have a higher boiling point than a branched chain.
b.A short, branched chain would have the lower boiling point. Although the bonds of a branched chain are easier to break than those of a straight chain, it would be more difficult to break more molecular bonds within the long chain, resulting in a higher boiling point.
c. A short, branched chain would have a lower boiling point. Straight chains have stronger intermolecular forces that hold together each molecule in contact, where as bonds between branched chains are more breakable due to the decreased intermolecular molecular forces between them.

3SBS #1-10, page 258

1) From a chemical viewpoint, why is petroleum sometimes considered "buried sunshine"?

Petroleum is sometimes cosidered "buried sunshine" because as a fossil fuel, it originates from biomolecules of prehistoric plants and animals. The energy released by burning petroleum represents energy originally captured from sunlight by these prehistoric green plants during photosynthesis; "buried sunshine".

2) Define and give one example of
a. potential energy
b. kinetic energy.

a. Potential energy is energy of position, or stored energy ready to be released. An example of potential energy is a the energy within an unreleased winded up spring toy.
b. Kinetic energy is energy related to motion. A car rolling down a hill is an example of kinetic energy (after the pedal on a breaked car, representing potential energy, is released).

3) In terms of chemical bonds, what happens during a chemical reaction?

Chemical energy, another form of potential energy, is stored within the bonds in chemical compounds. When an energy-releasing reaction takes place, the bonds break and reactant atoms reorganize to form new bonds and release energy. If more energy is released than originally started with, the reaction is exothermic, but if less energy is released than originally started with, the reaction is endothermic.

4) Based on its structural formula, which has more potential energy, a molecule of methane or a molecule of butane? Explain your answer.

A molecule of butane has more potential energy, it has more carbons than methane and a higher boiling point than methane. The bonds of butane are harder to break than the bonds of methane, resulting its higher potential energy.

5) Classify each of the following as primarily a demonstration of kinetic energy or potential energy:
a. a skateboard positioned at the top of a hill.
b. a charged battery in a flashlight that's turned off.
c. a rolling soccer ball.
d. gasoline in a parked car.
e. water flowing over a waterfall.

a. Potential energy.
b. Potential energy.
c. Kinetic energy.
d. Potential energy.
e. Kinetic energy.

6) Why is energy required to break chemical bonds?

Energy is required to break chemical bonds because it is what causes the reactant bonds to break and reorganize to form new bonds and energy.

7) For each of the following events, determine whether the reaction is exothermic or endothermic. Explain your answers in terms of bond breaking and bond making:
a. burning wood in a campfire.
b. cracking large hydrocarbon molecules.
c. digesting a candy bar.

a. Exothermic. More energy is released than is required to begin the chemical reaction.
b. Endothermic. More energy is required to crack large hydrocarbon molecules than is released.
c. Endothermic. It takes more energy to digest a candy bar than the energy released after digestion.

8) Burning a candle is an exothermic reaction. Explain this fact in terms of the quantity of energy stored in the bonds of the reactants compared with the quantity of energy stored in the bonds of the products.

The product of a burning candle yields more energy than the energy to begin the reaction with an unlit candle. Since more energy is let off than required to begin the reaction, burning a candle is an exothermic reaction.

9) Using Figure 3.24 on page 240 as a model, draw a potential energy diagram that illustrates the energy change when hydrogen gas reacts with oxygen gas to produce water and thermal energy.

See drawing.

10) State the law of conservation of energy.

The law of conservation of energy states that energy is neither created nor destroyed in any mechanical, physical, or chemical processes.