Questions and Answers of Chemistry The Central Science

Indicate whether each statement is true or false. (a) A reaction that is spontaneous in one direction will be nonspontaneous in the reverse direction under the same reaction conditions. (b)
Does the entropy of the system increase, decrease, or stay the same when (a) A solid melts, (b) A gas liquefies, (c) A solid sublimes?
The reaction 2Mg(s) + O2(g) → 2MgO(s) is highly spontaneous. A classmate calculates the entropy change for this reaction and obtains a large negative value for ΔS°. Did your classmate make a
(a) Write the chemical equations that correspond to ΔG°f for NH3(g) and for CO(g). (b) For which of these formation reactions will the value of ΔG°f be more positive (less negative) than
Which of the following statements is false?(a) Gases are far less dense than liquids.(b) Gases are far more compressible than liquids.(c) Because liquid water and liquid carbon tetrachloride do not
Liquids can interact with flat surfaces just as they can with capillary tubes; the cohesive forces within the liquid can be stronger or weaker than the adhesive forces between liquid and surface:(a)
(a) Are you more likely to see the density of a gas reported in g/mL, g/L, or kg/cm3? (b) Which units are appropriate for expressing atmospheric pressures, N, Pa, atm, kg/m2?(c) Which is most
Rank the following gases from least dense to most dense at 1.00 atm and 298 K: CO, N2O, Cl2, HF.
The atmospheric concentration of CO2 gas is presently 407 ppm (parts per million, by volume; that is, 407 L of every 106 L of the atmosphere are CO2). What is the mole fraction of CO2 in the
Which one or more of the following statements are true?(a) O2 will effuse faster than Cl2.(b) Effusion and diffusion are different names for the same process.(c) Perfume molecules travel to your nose
Which statement concerning the van der Waals constants a and b is true?(a) The magnitude of a relates to molecular volume, whereas b relates to attractions between molecules.(b) The magnitude of a
Two heating curves, A and B, are shown. In both cases, point 1 corresponds to the crystalline solid phase.(a) One of these graphs shows data for a liquid crystalline material. Which one? (b) In
Torricelli, who invented the barometer, used mercury in its construction because mercury has a very high density, which makes it possible to make a more compact barometer than one based on a less
The table below lists the density of O2 at various temperatures and at 1 atm. The normal melting point of O2 is 54 K.(a) Over what temperature range is O2 a solid? (b) Over what temperature
Carbon tetrachloride, CCl4, and chloroform, CHCl3, are common organic liquids. Carbon tetrachloride’s normal boiling point is 77°C; chloroform’s normal boiling point is 61°C. Which statement is
The table below shows the normal boiling points of benzene and benzene derivatives.(a) How many of these compounds exhibit dispersion interactions?(b) How many of these compounds exhibit
(a) What phase change is represented by the “heat of fusion” of a substance? (b) Is the heat of fusion endothermic or exothermic? (c) If you compare a substance’s heat of fusion to
Indicate whether each statement is true or false: (a) The critical pressure of a substance is the pressure at which it turns into a solid at room temperature. (b) The critical temperature
The table below shows some physical properties of halogenated liquids.Which of the following statements best explains these data?(a) The larger the dipole moment, the stronger the intermolecular
You are high up in the mountains and boil water to make some tea. However, when you drink your tea, it is not as hot as it should be. You try again and again, but the water is just not hot enough to
Indicate whether each statement is true or false: (a) The liquid crystal state is another phase of matter, just like solid, liquid, and gas. (b) Liquid crystalline molecules are generally
Which arrangement of atoms in a lattice represents close-packing? (i)
The unit cell of a compound containing potassium, aluminum, and fluorine is shown here.(a) What type of lattice does this crystal possess (all three lattice vectors are mutually
Covalent bonding occurs in both molecular and covalent-network solids. Which of the following statements best explains why these two kinds of solids differ so greatly in their hardness and melting
Imagine the primitive cubic lattice. Now imagine grabbing opposite corners and stretching it along the body diagonal while keeping the edge lengths equal. The three angles between the lattice vectors
Indicate the type of solid (molecular, metallic, ionic, or covalent-network) for each compound:(a) CaSO4, (b) Pd, (c) Ta2O5 (melting point, 1872 °C), (d) Caffeine (C8H10N4O2),(e)
Indicate the type of solid (molecular, metallic, ionic, or covalent network) for each compound:(a) InAs, (b) MgO, (c) HgS, (d) In, (e) HBr.
You are given a white substance that melts at 100 °C. The substance is soluble in water. Neither the solid nor the solution is a conductor of electricity. Which type of solid (molecular, metallic,
Amorphous silica, SiO2, has a density of about 2.2 g/cm3, whereas the density of crystalline quartz, another form of SiO2, is 2.65 g/cm3. Which of the following statements is the best explanation for
The densities of the elements K, Ca, Sc, and Ti are 0.86, 1.5, 3.2, and 4.5 g/cm3, respectively. One of these elements crystallizes in a body-centered cubic structure; the other three crystallize in
Calcium crystallizes in a face-centered cubic unit cell at room temperature that has an edge length of 5.588 Å.(a) Calculate the atomic radius of a calcium atom. (b) Calculate the density of Ca
Calculate the volume in Å3 of each of the following types of cubic unit cells if it is composed of atoms with an atomic radius of 1.82 Å. (a) Primitive (b) Face-centered cubic.
An element crystallizes in a face-centered cubic lattice. The edge of the unit cell is 4.078 Å, and the density of the crystal is 19.30 g/cm3. Calculate the atomic weight of the element and identify
An increase in temperature causes most metals to undergo thermal expansion, which means the volume of the metal increases upon heating. How does thermal expansion affect the unit cell length? What is
The polymer Kevlar, a condensation polymer, is used as reinforcement in car tires, strings of archery bows, and as a component of bulletproof vests.Draw the structures of the two monomers that yield
Arrange the following metals in increasing order of expected melting point: Mo, Zr, Y, Nb. Explain this trend in melting points.
Alabandite is a mineral composed of manganese(II) sulfide (MnS). The mineral adopts the rock salt structure. The length of an edge of the MnS unit cell is 5.223 Å at 25 °C. Determine the density of
The semiconductor CdSe has a band gap of 1.74 eV. What wavelength of light would be emitted from an LED made from CdSe? What region of the electromagnetic spectrum is this?
Write a balanced chemical equation for the formation of a polymer via a condensation reaction from the monomers succinic acid (HOOCCH2CH2COOH) and ethylenediamine (H2NCH2CH2NH2).
Sodium oxide (Na2O) adopts a cubic structure with Na atoms represented by green spheres and O atoms by red spheres.(a) How many atoms of each type are there in the unit cell?(b) Determine the
An ideal quantum dot for use in TVs does not contain any cadmium due to concerns about disposal. One potential material for this purpose is InP, which adopts the zinc blende (ZnS) structure
Selected chlorides have the following melting points: NaCl (801 °C), MgCl2 (714 °C), PCl3 (-94 °C), SCl2 (-121 °C)(a) For each compound, indicate what type its solid form is (molecular, metallic,
Cinnabar (HgS) was utilized as a pigment known as vermillion. It has a band gap of 2.20 eV near room temperature for the bulk solid. What wavelength of light (in nm) would a photon of this energy
Energy bands are considered continuous due to the large number of closely spaced energy levels. The range of energy levels in a crystal of copper is approximately 1 x 10–19 J. Assuming equal
One method to synthesize ionic solids is by the heating of two reactants at high temperatures. Consider the reaction of FeO with TiO2 to form FeTiO3. Determine the amount of each of the two reactants
Write an equation for the second electron affinity of chlorine. Would you predict a positive or a negative energy value for this process? Is it possible to directly measure the second electron
Gold is isolated from rocks by reaction with aqueous cyanide, CN-: 4 Au(s) + 8 NaCN(aq) + O2(g) + H2O(l) → 4 Na[Au(CN)2](aq) + 4 NaOH(aq). (a) Which atoms from which compounds are being
Would you expect manganese(II) oxide, MnO, to react more readily with HCl(aq) or NaOH(aq)?
Energy is required to remove two electrons from Ca to form Ca2+, and energy is required to add two electrons to O to form O2 -. Yet CaO is stable relative to the free elements. Which statement is the
Musical instruments like trumpets and trombones are made from an alloy called brass. Brass is composed of copper and zinc atoms and appears homogeneous under an optical microscope. The approximate
Consider the two spheres shown here, one made of silver and the other of aluminum. (a) What is the mass of each sphere in kg? (b) The force of gravity acting on an object is F = mg, where m
Two beakers contain clear, colorless liquids. When the contents of the beakers are mixed a white solid is formed. (a) Is this an example of a chemical or a physical change? (b) What would
Two positively charged particles are first brought close together and then released. Once released, the repulsion between particles causes them to move away from each other. (a) This is an
For each of the following processes, does the potential energy of the object(s) increase or decrease? (a) The distance between two oppositely charged particles is increased. (b) Water is
(a) Which is more likely to eventually be shown to be incorrect: an hypothesis or a theory? (b) A(n) _________ reliably predicts the behavior of matter, while a(n) _________ provides an
Is the use of significant figures in each of the following statements appropriate? (a) The 2005 circulation of National Geographic was 7,812,564. (b) On July 1, 2005, the population of Cook
A 1.0-g sample of carbon dioxide (CO2) is fully decomposed into its elements, yielding 0.273 g of carbon and 0.727 g of oxygen. (a) What is the ratio of the mass of O to C? (b) If a sample
Consider an atom of 10B. (a) How many protons, neutrons, and electrons does this atom contain? (b) What is the symbol of the atom obtained by adding one proton to 10B? (c) What is the
Consider the mass spectrometer shown in Figure 2.11. Determine whether each of the following statements is true or false. If false, correct the statement to make it true: (a) The paths of
The structural formulas of the compounds n-butane and isobutane are shown below. (a) Determine the molecular formula of each. (b) Determine the empirical formula of each. (c) Which
Consider an atom of 63Cu. (a) How many protons, neutrons, and electrons does this atom contain? (b) What is the symbol of the ion obtained by removing two electrons from 63Cu? (c) What
Ball-and-stick representations of benzene, a colorless liquid often used in organic chemistry reactions, and acetylene, a gas used as a fuel for high-temperature welding, are shown below. (a)
Consider the following organic substances: ethanol, propane, hexane, and propanol. (a) Which of these molecules contains an OH group? (b) Which of these molecules contains three carbon
Write “true” or “false” for each statement. (a) We balance chemical equations as we do because energy must be conserved. (b) If the reaction 2 O3(g) → 3 O2(g) goes to completion
The thermite reaction, Fe2O3 + Al → Al2O3 + Fe produces so much heat that the Fe product melts. This reaction is used industrially to weld metal parts under water, where a torch cannot be employed.
Write “true” or “false” for each statement. (a) A mole of horses contain a mole of horse legs. (b) A mole of water has a mass of 18.0 g. (c) The mass of 1 molecule of water is
Neurotransmitters are molecules that are released by nerve cells to other cells in our bodies, and are needed for muscle motion, thinking, feeling, and memory. Dopamine is a common neurotransmitter
The semiconductor gallium arsenide, GaAs, is used in highspeed integrated circuits, light-emitting diodes, and solar cells. Its density is 5.32 g/cm3. It can be made by reacting trimethylgallium,
An aqueous solution contains 1.2 mM of total ions. (a) If the solution is NaCl(aq), what is the concentration of chloride ion? (b) If the solution is FeCl3(aq), what is the concentration of
With the exception of helium, the noble gases condense to form solids when they are cooled sufficiently. At temperatures below 83 K, argon forms a close-packed solid whose structure is shown
Which of the following solutions is the most acidic? (a) 0.2 M LiOH, (b) 0.2 M HI, (c) 1.0 M methanol (CH3OH).
You make 1.000 L of an aqueous solution that contains 35.0 g of sucrose (C12H22O11). (a) What is the molarity of sucrose in this solution? (b) How many liters of water would you have to add
Bronze is a solid solution of Cu(s) and Sn(s); solutions of metals like this that are solids are called alloys. There is a range of compositions over which the solution is considered a bronze.
In 2014, a major chemical leak at a facility in West Virginia released 7500 gallons of MCHM (4-methylcyclohexylmethanol, C8H16O) into the Elk River. The density of MCHM is 0.9074 g/mL. (a)
Which quantity must be determined experimentally in order to determine the bonding atomic radius of an atom? (a) The distance from the nucleus where the probability of finding an electron goes
Provide a brief explanation for each of the following: (a) O2- is larger than O. (b) S2- is larger than O2-. (c) S2- is larger than K+. (d) K+ is larger than Ca2+.
Which element has the highest second ionization energy: Li, K, or Be?
Would a neutral K atom or a K+ ion have a more negative value of electron affinity?
Using Lewis symbols and Lewis structures, diagram the formation of SiCl4 from Si and Cl atoms, showing valence-shell electrons. (a) How many valence electrons does Si have initially? (b)
Use Lewis symbols and Lewis structures to diagram the formation of PF3 from P and F atoms, showing valence-shell electrons. (a) How many valence electrons does P have initially? (b) How
(a) What is the trend in electronegativity going from left to right in a row of the periodic table? (b) How do electronegativity values generally vary going down a column in the periodic
True or false: (a) The C-C bonds in benzene are all the same length and correspond to typical single C-C bond lengths. (b) The C-C bond in acetylene, HCCH, is longer than the average C-C
(a) Which of these compounds is an exception to the octet rule: carbon dioxide, water, ammonia, phosphorus trifluoride, or arsenic pentafluoride? (b) Which of these compounds or ions is an
For Group 3A–7A elements in the third row of the periodic table and beyond, the octet rule is often not obeyed. A friend of yours says this is because these heavier elements are more likely to make
There are many Lewis structures you could draw for sulfuric acid, H2SO4 (each H is bonded to an O). (a) What Lewis structure(s) would you draw to satisfy the octet rule?(b) What Lewis
Draw the Lewis structures for each of the following ions or molecules. Identify those in which the octet rule is not obeyed; state which atom in each compound does not follow the octet rule; and
State whether each of these statements is true or false. (a) A carbon–carbon triple bond is shorter than a carbon–carbon single bond. (b) There are exactly six bonding electrons in the
State whether each of these statements is true or false.(a) The longer the bond, the larger the bond enthalpy.(b) C—C bonds are stronger than C—H bonds. (c) A typical single bond length is
We can define average bond enthalpies and bond lengths for ionic bonds, just like we have for covalent bonds. Which ionic bond is predicted to be stronger, Na—Cl or Ca—O?
We can define average bond enthalpies and bond lengths for ionic bonds, just like we have for covalent bonds. Which ionic bond is predicted to have the smaller bond enthalpy, Li—F or Cs—F?
A carbene is a compound that has a carbon bonded to two atoms and a lone pair remaining on the carbon. Many carbenes are very reactive. (a) Draw the Lewis structure for the simplest carbene,
Draw the Lewis structure for NO+ . Is the nitrogen– oxygen bond in NO+ longer, shorter, or the same length as the nitrogen–oxygen bond in NO? Explain.
A new compound is made that has a C—C bond length of 1.15 Å. Is this bond likely to be a single, double, or triple C—C bond?
A new compound is made that has an N—N bond length of 1.26 Å. Is this bond likely to be a single, double, or triple N—N bond?
Consider the lattice energies of the following Group 2A compounds: BeH2, 3205 kJ/mol; MgH2, 2791 kJ/mol; CaH2, 2410 kJ/mol; SrH2, 2250 kJ/mol; BaH2, 2121 kJ/mol.(a) What is the oxidation number of H
Although I3- is a known ion, F3- is not. (a) Draw the Lewis structure for I3- (it is linear, not a triangle). (b) One of your classmates says that F3- does not exist because F is too
The hypochlorite ion, ClO-, is the active ingredient in bleach. The perchlorate ion, ClO4-, is a main component of rocket propellants. Draw Lewis structures for both ions.(a) What is the formal
(a) Draw the Lewis structure for hydrogen peroxide, H2O2.(b) What is the weakest bond in hydrogen peroxide? (c) Hydrogen peroxide is sold commercially as an aqueous solution in brown bottles to
Formic acid has the chemical formula HCOOH. It is a colorless liquid that has a density of 1.220 g/mL. (a) The carbon atom in formic acid is bound to one H and both O’s. Draw the Lewis
Ammonium chloride, NH4Cl, is a very soluble salt in water.(a) Draw the Lewis structures of the ammonium and chloride ions. (b) Is there an N—Cl bond in solid ammonium chloride?(c) If you

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