Chapter 5 and 6 questions

Question 1

Life on our planet depends on water. Explain each of the following statements.
A) bodies of water act as heat reservoirs, moderating climate
B) ice protects ecosystems in lakes because it floats rather than sinks

Answer 1

A) because water has such a high specific heat, it can moderate climate by capturing and absorbing heat from surrounding land and air
B) if ice were denser than liquid water, it would sink as it forms. As a result, lakes would freeze from the bottom up, killing forms of life that could not tolerate freezing temperatures

Question 2

The following are four pairs of atoms. Consult table 5.1 to answer these questions
-> N and C
-> S and O
-> N and H
-> S and F
A) what is the electro negativity difference between atoms
B) assume that a single covalent bond forms between each pair of atoms. Which atom attracts the electron pair in the bond more strongly?
C) Arrange the bonds in order of increasing polarity

Answer 2

A) N and C, 3.0-2.5 = 0.5
F and S, 4.0-2.5 = 1.5
O and S, 3.5-2.5 = 1
N and H, 3.0-2.1 = 0.9
B) N more strongly attracts electrons than C
F more strongly attracts electrons that S
O more strongly attracts electrons than S
N more strongly attracts electrons than H
C) N-C < N-H < S-O < S-F

Question 3

In some cases, the boiling point of a substance increases with its molar mass
A) does this hold true for hydrocarbons?
B) Based on the molar masses of H2O, N2, O2, and CO2, which would you expect to have the lowest boiling point?
C) unlike N2, O2, and CO2, water is a liquid at room temperature. Explain.

Answer 3

A) Yes this is true for hydrocarbons. Distillation towers at a petroleum refinery separate hydrocarbons of different sizes by their boiling point. CH4 boils at -161.5 degrees C, C4H10 boils at -1 degree C, C8H8 boils at 125 degrees C
B) based only on molar mass, you would expect H2O to have the lowest boiling point because its molar mass is the lowest at 18.0 g/mol
C) Water is a polar molecule while the rest are non polar. Both its geometry and its polar covalent bonds contribute to the formation of strong intermolecular forces. Thus, molar mass is not the only factor that contributes to the boiling point of a substance

Question 4

This diagram represents two water molecules in a liquid state. What kind of boding force does the arrow between hydrogen and oxygen indicate?/

Answer 4

The arrow points to a hydrogen bond, an example of an attraction force between water molecules and not within each water molecule (as is the case for the polar covalent bond O-H bond)

Question 5

Dishwashing detergent (1.o3 Density, g/ml)
Maple syrup (1.37 Density, g/ml)
Vegetable oil (0.91 density, g/ml)
A) If you pour equal volumes of these three liquids into a 250-ml graduated cylinder, in what order should you add the liquids to create 3 separate layers?
B) predict what would happen if a volume of water equal to the other liquids were poured into the cylinder in part a and the contents then were mixed vigorously

Answer 5

A) Adding the liquids in this order: maple syrup, dishwashing detergent, and then vegetable oil (most to least dense). Three factors need to be considered: solubility, density, and the care with which each liquid is poured. Maple syrup will probably slowly dissolve in dishwashing liquid; likewise vegetable oil may be slightly soluble in the detergent. Be careful with pouring, these three liquids should not easily mix and probably could be added in any order.
B) After vigorous mixing, a cloudy emulsion most likely will form. Over time, it will separate into two layers: one with maple syrup and some of the detergent dissolved in water, one with the rest of the detergent dissolved in oil.

Question 6

Predict what will happen when each of these dilute solutions is tested for conductivity. Explain your predictions briefly
CaCl2(aq)
C2H5OH(aq)
H2SO4(aq)

Answer 6

A) the solution will conduct electricity and the bulb will light. based on Table 5.5, CaCl2 is a soluble salt and therefore releases calcium ions (Ca2+ and Cl-) when it dissolved. These ions carry a current
B) The solution will not conduct electricity. Although ethanol (C2H5OH) is soluble in water, it is a covalent compound and does not form ions
C) The solution will conduct electricity and the bulb will light. Sulfuric acid (H2SO4) releases ions when it dissolves. H+ and SO4^2-

Question 7

Based on the generalizations in table 5.5, which compounds are likely to be water soluble
KC2H3O2
LiOH
Ca(NO3)2
Na2SO4

Answer 7

All of these compounds are water soluble

Question 8

Classify the following aqueous solutions as acidic, neutral, or basic
HI(aq)
NaCl(aq)
NH4OH(aq)

Answer 8

HI is acidic, [H+] = [I^-] > [OH^-]
NaCl is neutral, [Na+] = [Cl^-] and [H^+] = [OH^-]
NH4OH is basic, [NH4^+] = [OH^-] > [H^+]

Question 9

In each pair below, the [H^+] is different. By what factor of 10 is it different?
A) pH = 6 and pH = 8
B) pH = 5.5 and pH = 6.5
C) [H^+] = 1 x 10^-8 M and [H+] = 1 x 10^-6
D) [OH^-] = 1 x 10^-2 M and [OH^-] = 1 x 10 ^-3 M

Answer 9

A) 6 has 100 times more than 8
B) 5.5 has 10 times more than 6.5
C) 100 times more
D) 10 times more

Question 10

Which gas is dissolved in water to produce each of the following acids
A) carbonic acid, H2CO3
B) sulfurous acid, H2SO3

Answer 10

A) carbonic acid = CO2 (CO2 +H2O -> H2CO3)
B) sulfur dioxide = SO2 (SO2 +H2O -> H2SO3)

Question 11

Propose an explanation for the fact that NH3, like H2O, has an unexpectedly high specific heat

Answer 11

Like water, NH3 is a polar molecule. It has polar N-H bonds and a trigonal pyramidal geometry. Therefore, despite its lower molar mass, considerable energy must be added to liquid NH3 to overcome the intermolecular forces (hydrogen bonding) among NH3 molecules

Question 12

Health goals for contaminant in drinking water are expressed as MCLG, or maximum contaminant level goals. Legal limits are given as MCL, or maximum contaminant level. How are MCLG and MCL related for a oven contaminant

Answer 12

For a given contaminant, the MCLG (a goal) and the MCL (a legal limit) are usually the same. However, the levels may differ when it is not practical or possible to achieve the health goal as set by the MCLG. This sometimes is the case for carsinogens, for which the MCLG is set at zero (under the assumption that any exposure presents a cancer risk)

Question 13

A) is glycine a polar or non polar molecule
B) can glycine exhibit hydrogen bonding?
C) Is glycine soluble in water?

Answer 13

A) Glycine contains several polar bonds and has several areas in its molecule (everything but the -CH2 region)
B) yes, hydrogen bonding is possible when O-H and N-H bonds are present, both of which are in glycine
C) because glycine has polar bonds located in several areas of the molecule and has a relatively small molar mass, glycine should be soluble in water

Question 14

Electronegativity

Answer 14

A measure of an atom’s attraction for the electrons it shares in a covalent bond
EN values on the periodic table further you go to the right and further you go up the more EN increases

Question 15

H-bonds
Covalent bonds

Answer 15

H-bonds - intermolecular bonds
Covalent bonds - intramolecular bonds

Question 16

2: the combustion of coal releases several substances into the air
A) of these substances one is a gas that is produced in large amounts. Give its chemical formula and name
B) In contrast, the amount of SO2 (sulfur dioxide) released is relatively small. Even so, this SO2 is of concern. Why?
C) another gas produced is in small amounts of NO. What is the origin of nitrogen in NO?
D) when coal burns, fine particles of soot may be released, what are the health concerns with PM2.5 the smallest of these particles

Answer 16

A) CO2, carbon dioxide
B) SO2 is an air pollutant. Although sulfur is present in low concentrations in coal, large amounts of coal are burned, and collectively large amounts of SO2 are released.
C) Nitrogen is present in the air (-80% of atmospheric gases). The nitrogen present in air reacts with O2 (also N2 +O2 ->(high temperature) 2NO present in air) at high temperatures to form NO
D) Long-term exposures, such as those experienced by people living for many years in areas with high particle levels, have been associate with problems such as lung function and the development of chronic bronchitis and even sometimes premature deaths

Question 17

4: Energy exists in different forms in our natural world. In figure 6.9 identify where:
A) potential (stored) energy of the fuel is converted to heat
B) kinetic energy of water molecules is converted into mechanical energy
C) mechanical energy is converted into electrical energy
D) Electrical energy is converted into forms such as heat and light

Answer 17

A) The fuel in the burner is a source of potential energy. When burned, some of it potential energy is converted into heat through combustion. The heat is inverted into kinetic energy of the vaporized water molecules (steam).
B) The kinetic energy of the steam is converted into mechanical energy by spinning a turbine
C) The mechanical energy generated from the spinning turbine is converted into electrical energy by rotating a wire in a magnetic field
D) The electrical energy, is carried to the city by the power lines, light bulbs, and heat in homes

Question 18

9: Mercury (Hg) is present in trace amounts in coal, ranging from 50 to 200 ppb. Consider the amount of coal burned by the power plant in Your Turn 6.20. Calculate tons of mercury in the coal based on the lower (50ppb) and the higher (200ppb) concentrations

Answer 18

A typical power plant burns 1.5 million tons of coal each year. The first calculation is for coal with 50 ppb mercury; the second is for 200 ppb.
X ton Hg/1.5 x 10^6 ton coal = 50 ton Hg/1 x 10^9 ton coal = 0.075 ton Hg
X ton Hg/1.5 x 10^6 ton coal = 200 ton Hg/1 x 10^9 ton coal = 0.30 ton Hg
Assuming mercury concentrations in the range of 50-200 ppb, the plan releases between 0.075 and 0.30 tons of Hg per year

Question 19

13

Answer 19

drawing

Question 20

14: consider Pentane, C5H12, triacontane C30H62, and propane C3H8 at room temperature (25 degrees celcius), categorize each as solid, liquid, or gas

Answer 20

• Pentane should be a liquid because room temperature (20 degrees Celsius) is below its boiling point (36 degrees Celsius)
• Triacontane should be a solid at room temperature because room temperature is below its melting point of (66 degrees Celsius)
• Propane should be a gas because room temperature is above its boiling point (-42 degrees Celsius)

Question 21

17:
A) write the balanced chemical equation for the combustion of n-heptane C7H16
B) rewrite using lewis structures
C) the heat of combustion for methane, C2H6 is 52kJ/g. How much heat is produced is 1.0 mol of ethane undergoes complete combustion

Answer 21

A) C7H16 + 11O2 -> 7 CO2 + 8H2O
B) 2.50 kg x 10^3g/kg x 1mol C7H16/100.2 grams x 4817 kJ/ 1mol C7H16 = 1.2 x 10^7 kJ

Question 22

19: A 12-oz serving of a soft drink has an energy equivalent to 92kcal. In kilojules, what is the energy released when metabolizing this beverage

Answer 22

92kcal x 4.184kJ/1kcal = 380kJ

Question 23

20: State whether these processes are endothermic or exothermic?
A) charcoal burns in an outdoor grill
B) water evaporates on your skin
C) glucose is synthesized in the leaves of a plant by photosynthesis

Answer 23

A) exothermic
B) endothermic
C) endothermic

Question 24

21:use the bond energies in table 6.2 to calculate the energy changes associated with each of these reactions. label them as endothermic or exothermic
A) 2H2(g) + CO(g) -> CH3OH(g)
B) H2(g) +O2(g) -> H2O2(g)
C) 2BrCl(g) -> Br2(g) +Cl2(g)

Answer 24

A) bonds will be broken in the reactants:
1 mole of triple bonded N 1(946 kJ) = 946 kJ
3 mole of H single bonded = 3(436) kJ) = 1308 kJ
The total energy absorbed in breaking bonds = 2254 kJ
Bonds formed in products:
6 mole N-H single bond = 6(391 kJ) = 2346 kJ
Total energy released in forming bonds = 2346 kJ
Net energy change is (+2254 kJ) +(-2346 kJ) = -92kJ
The overall energy change is negative. Exothermic
B) Bonds broken in reactants:
1 mole H single bonds = 1(436 kJ) = 436 kJ
1 mole Cl single bonds = 1(242 kJ) = 242 kJ
Total energy released in forming bonds = 678 Kj
Net energy change is (+678 kJ) +(-862 kJ) = -184 kJ
The overall energy is negative. Exothermic

Question 25

24: here are the strucutal formulas for ethane, ethene and ethanol
A) is ethane an isomer of ethene? Or ethanol?
B) Are any other isomers possible for ethene?
C) Are any other isomers possible for ethanol

Answer 25

A) none of these are isomers. all have different chemical formulas
B) no, no other isomers are possible for ethene
C) one other isomer is possible, although it contains a very distinct functional group, called an ether. It’s condensed structural formula is Ch3-O-CH3

Question 26

25:
A) for each compound, draw structural formulas that show missing H atoms, all should have 18 H atoms
B) which if any of these structural formulas are identical
C) draw

Answer 26

B) the second and third are identical
C) several isomers are possible

Question 27

28: C16H34 -> C5H12 + C11H22
A) which bonds are broken and which bonds are formed in this reaction
B) use the info in table 6.2 to calculate the energy change during cracking reaction

Answer 27

A) The c-c single bond in the center of the molecule of one of the C-H single bonds must be broken. A second C-C double bond can be formed in its place. A new C-H single bond must form on the shorted product
B) bonds broken in reactants:
2 mol C-C single bonds = 2(356 kJ) = 712 kJ
1 mol C-H single bonds = 1(416 kJ) = 416 kJ
Total energy absorbed in breaking bonds = 1128 kJ

Bonds formed in the products:
1 mol C-H single bonds = 1(416 kJ) = 416 kJ
1 mol C-C double bonds = 1(598 kJ) = 598 kJ
Total energy released in the forming bond = 1014 kJ
Net energy change is (1128 kJ)+ (-1014 kJ) = 114kJ
The overall energy is positive -> endothermic

Question 28

32: when glucose, is “burned” (metabolized) in your body, the products are carbon dioxide and water
A) the source
B) the chemical reaction that produces the fuel
C) the combustion products
D) the solubility in water

Answer 28

A) C6H12O6 +6O2 -> 6 CO2 + 6 H2O + energy
B) cellulose is one of the primary components of wood. Cellulose is a polymer made up of glucose building blocks. As a result, burning cellulose give products comparable to burning glucose.

Question 29

45: Use the bond energies in Table 6.2 to explain why chlorofluorocarbons (CFCs) are so stable. Also explain why it takes less energy to release Cl atoms from CFCs than it does to release F atoms and connect this to HFCs as replacements for CFCs

Answer 29

CFCs are stable because the bond energies for C-Cl and C-F are large compared to other bond energies. It takes less energy to release Cl atoms from CFCs because the C-Cl bond energy (327 kJ/mol) is lower than the C-F bond energy (485 kJ/mol). HFCs, with their C-F bonds (no C-Cl bonds), release no Cl atoms

Question 30

47: the energy content of fuels can be expressed in kilojoules per gram (kJ/g), as shown in Figure 6.5, from these values, how do fuels containing oxygen compare to those that do no? Now calculate the energy content for each of these fuels in kilojoules per mole (kJ/mol). What trend do you now observe?

Answer 30

Methane (CH4): 50.1kJ/1g x 16.05g/1mol = 802 kJ/mol

Octane (C8H18): 44.4kJ/1g x 114 g/ 1 mol = 5.06 x 10^3 kJ/mol

Coal (C135H96O9NS): 32.8kJ/1g x 1908g/1mol = 6.26 x 10^4 kJ/mol

Ethanol (C2H6O): 26.8kJ/1g x 46g/1mol = 1.23 x 10^3 kJ/mol

Glucose (C6H12O6): 14.1kJ/1g x 180g/1 mol = 2.54 x 10^3 kJ/mol

Question 31

When energy is released during the course of a chemical reaction, what is the reaction

Answer 31

The reaction is said to be exothermic

Question 32

Kinetic
Potential

Answer 32

Kinetic energy - temperature
Potential energy - position

Question 33

The first law states?

Answer 33

It is consistent with what flowing in either direction. This is because the first law simply states that no heat can be lost from a system without being accounted for at another system
- the first law is NOT sufficient to predicts the direction in which a reaction would proceed

Question 34

Second law of thermodynamics

Answer 34

• entropy is the measure of disorder in a system. An increase in entropy is an increase in the disorder of the system.
• the concept of entropy is essential for predicting the direction a reaction is likely to take
• system tend to move from ordered to disordered, reversible processes do not change the entropy of a system, whereas irreversible ceases increase the entropy of a system, reactions tend to proceed towards equilibrium, which is a state of minimum potential energy

Question 35

Systems can do what in the second law of thermodynamics

Answer 35

• systems can increase their order only at the expense of energy
• application of energy to the system can result in an increased order within the system by further disorder to the surroundings

Question 36

1 calorie =
1 kcal =

Answer 36

1 calorie = 4.184J
1 kcal = 1000 cal

Question 37

Bond energy

Answer 37

The amount of energy that must be absorbed to break a chemical bond

Question 38

Bond yielding
Bond breaking

Answer 38

Bond yielding - exothermic
Bond breaking - endothermic

Question 39

according to section 6.3, what is the definition of energy?

Answer 39

According to section 6.3, energy refers to the ability or capacity of matter to do work or to produce change.

Question 40

what is the difference between kinetic and potential energy

Answer 40

Kinetic energy is energy of motion that is required in things like walking. While potential energy is stored energy, or energy of position that is in position in respect to another object. Potential energy is the energy that is typically stored in chemical bonds in a molecule that can be released during a chemical reaction.

Question 41

what is the difference between heat and temperature

Answer 41

Heat is kinetic energy that flows from hotter objects to colder ones. While temperature is a measure of the average kinetic energy of the atoms and/or molecules that can be present in any substance.

Question 42

according to section 6.4, what is a exothermic reaction

Answer 42

Exothermic reactions have to do with describing any chemical or physical change that is accompanied by the release of heat.

Question 43

is photosynthesis exothermic or endothermic

Answer 43

Photosynthesis is a endothermic reaction. This is because an endothermic reaction is one in which a physical or chemical change absorbs energy to in turn create products that have a higher energy state. This being said photosynthesis cannot occur without energy from the sun, so it has to be a endothermic reaction. Photosynthesis cannot be an exothermic reaction because sunlight is absorbed not released.

Question 44

according to table 6.2, how much energy is required to break the double bond in diatomic oxygen?

Answer 44

it would take 498kJ to break the double bond in the diatomic oxygen

Question 45

According to table 6.2, how much energy is given off when one mole of CO2 is formed? CO2 has two C=O double bonds.

Answer 45

According to the table, 1606 kJ/mol are given off when one mole of CO2 is formed.

Question 46

according to section 6.5, what is a state function

Answer 46

according to section 6.5 state function is defined as being energy change that accompanies a chemical reaction

Question 47

how does temperature change in a distillation column, as the molecules move from the bottom to the top

Answer 47

According to figure 6.24, as the molecules move from the bottom to the top, the saturation temperature decreases. Meaning that the lightest section collected from is the refinery gasses, and the heaviest fraction in the distillation tower collected comes from asphalt. This is because things like diesel and jet fuel have a higher boiling point than something like refinery gases it goes in order. Those at the top will vaporize and rise the quickest.

Question 48

how does the length of the condensed hydrocarbons change in a distillation column as the molecules move from top to bottom

Answer 48

According to figure 6.24, The length of the hydrocarbon decreases from the bottom to the top. This is because the longer hydrocarbon condenses at a higher temperatures, and the shorter hydrocarbon condenses at lower temperatures. The figure shows that the further up in the tower it goes the more spread out the hydrocarbons are due to the amount of space the hydrocarbons take up. In gases, they are less likely to be packed closer together, as they are in asphalt, which means the length of the condensed hydrocarbons increases from the bottom of the distillation column to the top.

Question 49

how is the boiling point of water different from the boiling point of the substances that had a similar molecular weight

Answer 49

While water boils at 100 degrees Celsius and is a liquid at room temperature, other substances like hydrogen sulfide boil at -60 degrees Celsius and is a gas at room temperature. This seems to be affected by whether there are hydrogen bonds present in the compounds.

Question 50

the electrons involved in the covalent O-H bond of water are likely to be found near which of the elements that for the bond?

Answer 50

The covalent O-H bond of water is likely to be found near oxygen in the bond. This is because Hydrogen helps to complete Oxygens valence shell and helps to then empty hydrogens valence shell.

Question 51

what atoms are needed for a hydrogen bond to form

Answer 51

A hydrogen bond is an attraction between an H atom, and a highly electronegative atom like O, N, or F (because of their location on the periodic table they attract electrons that are stronger).

Question 52

how strong is a hydrogen bond, in comparison to a covalent bond

Answer 52

Typically, it is said that a hydrogen bond is only one-tenth as strong as covalent bonds which connects atoms within molecules.

Question 53

water has a high specific heat. How does this affect the climate in regions bordering large bodies of water?

Answer 53

When a region is bordered by a large body of water, the specific heat of water can influence evaporation and the absorption of heat in certain bodies of water. This can contribute to the temperature conditions to allow the ground to cool quicker when the temperature cools.
It has a temperate effect on the weather. Water traps heat and releases it when air is cold, and absorbs heat when the air is warm.

Question 54

what is a water footprint

Answer 54

A water footprint is an estimate of the volume of fresh water that is used to produce goods or to provide a service.

Question 55

which U.S. government agency is charged with the determination and regulation of water safety standards?

Answer 55

the U.S. environmental protection agency oversees the determination and regulation of water safety

Question 56

what is the difference in solubility between nitrate-containing ionic compounds and hydroxide-containing ionic compounds

Answer 56

Hydroxide-containing ionic compounds are mostly insoluble, and the exceptions are Group 1 metals, and NH4+. Whereas nitrate-containing ionic compounds are all soluble and there are no exceptions.

Question 57

do molecular compounds break up into charged species when dissolved in water

Answer 57

Molecular compounds dissolve in water, but do not break up into ions. Molecular compounds can break up evenly in the water. They can break into individual atoms or evenly distribute across the water, but do not dissolve completely.

Question 58

what makes carbonic acid an acid

Answer 58

Carbonic acid is an acid because as CO2 dissolves in water it releases hydrogen ions. This means that carbonic acid is a weak acid that releases hydrogen ions as it dissolves which also means that it does not entirely dissolve in water.

Question 59

why is the reaction shown in figure 5.9, referred to as a neutralization reaction?

Answer 59

This is because the reaction shown in the equation is a chemical reaction in which the protons from an acid combine with the hydroxide ions from a base to form water molecules.