UNIT 3 MIDTERM EXAM
What is the charge of iron (Fe) in the compound Fe2O3?
+3
Which of the following is a correct and balanced equation showing the reaction of calcium and oxygen? (While several of the equations may be balanced, only one has the correct products and reactants as well as being correctly balanced.)
2Ca+O2=2CaO
Dispersion forces are stronger than covalent bonds
False
When you compare the mass of the products to the mass of the reactants in a fission reaction, what do you find? (Note the question is asking about mass, not mass number.)
The reactants have more mass.
Rank the following according to their strength, weakest first, strongest last.
dispersion forces, dipole-dipole interactions, hydrogen bonding, covalent bonding
A very fast reaction has a very high activation energy?
false
In a bonding orbital between two atoms, where is the electron density the highest? (Where do you have the highest probability of detecting an electron?)
in between the two atoms
An ice cube melts in a glass of warm water. This is an example of which type of process?
irreversible
The various forms of energy can be ranked according to their level of what?
organization
An unstable nucleus which has a tendency to spontaneously change its form with the emission of high-energy particles or photons is said to be
radioactive
Which is the best definition of an alloy?
solid mixture of metals
The process known as nuclear fission is primarily responsible for
the energy produced by a nuclear reactor.
Which of the following is the best description of activation energy?
the energy that must be put into a system before a reaction can take place
An energy diagram for the magnesium-oxygen reaction is shown to the right. Sodium will also react with oxygen. However, unlike magnesium, sodium reacts immediately when it is exposed to oxygen and produces very little heat and no visible light. Which of the curves below best represents the sodium-oxygen reaction compared with the magnesium-oxygen reaction to the right? (The curve for magnesium + oxygen is shown in light grey for reference.)
the graph that shows higher energy release and energy loss for Mg+O than for Na+O
In lesson 20, a magnesium strip was used to ignite the thermite reaction. When magnesium is placed in a flame from a small blow torch, it burns quite brightly, forming magnesium oxide, a salt that contains one magnesium for every oxygen. The following questions ask you to provide some details of the chemical processes involved in a reaction between magnesium and oxygen. 2. What happens to the valence electrons as the product (MgO) is formed?
the magnesium atoms' valence electrons are effectively transferred to oxygen
What happens to the valence electrons as an ionic compound is formed?
the metal atoms; valence electrons are effectively transferred to the nonmetal
The oxidation state of an atom refers to
the number of electrons gained or lost when an ionic bond is formed
In the equation C2H4 + 3O2 = ? CO2 + 2H2O, how many CO2 molecules are needed to balance the equation?
2
From the graphical information in this radioactive decay chart, estimate the half-life of the radioactive element whose decay curve is plotted.
2.5 years (lesson 25 quiz #4)
Each molecule of nitric acid has the formula HNO3. If there are 6000 oxygen atoms present and 6000 nitrogen atoms present, how many hydrogen atoms will be required to convert all of the oxygen atoms into nitric acid?
2000
Uranium-238 alpha decays, emitting a helium-4 nucleus. What is the mass number of the product?
234
In which of the following processes is the end product more ordered than the reactants? (In which process does entropy decrease in the system?)
2H2 (gas) + O2 (gas) = 2 H2O (gas)
Which of the following is a legitimate radioactive decay because both charge and mass number are conserved?
84212Po → 82208Pb + 24He
In order for a chemical reaction to occur
? (lesson 20 quiz)
Look at the diagram of a silicate mineral with Synthesis Question #5 in your textbook. Make a prediction about whether this mineral would appear as fibers, layers, or no regular pattern.
? Lesson 24 quiz #4
Pull out your textbook for this one! Which of the following structures would form a mineral such as mica that will flake off in sheets?
? Lesson 24 quiz #5
These are drawings of several different fatty acids. Small white balls are H atoms, large gray balls are oxygen atoms, and small gray balls are carbon atoms. The next two questions test your understanding of fatty acids and their properties.
? lesson 24 quiz #3
What is the formula for ethene?
C2H4
For the pictures of molecules, the gray balls represent carbon atoms and the white balls are hydrogen atoms. The molecules belong to a family called the hydrocarbons. These next three questions test if you can recognize patterns in molecular families and bonding around carbon atoms and then reason from them to make predictions. Ethene = Propylene = Butylene = 3. The chemical formula of the next family member after butylene will have what chemical formula?
CH2CHCH2CH2CH3 (also written C5H10)
Which of the equations below is balanced correctly?
CH4 +2O2 ⇒ CO2 + 2H2O
What happens to the entropy of the universe as the products are formed?
Chemical potential energy is converted into thermal energy resulting in an increase in entropy.
Which of the following substances is most likely to be a pure element?
Copper
Why is a high temperature required for nuclear fusion to occur?
High temperatures are required to allow the nuclei to have enough kinetic energy to overcome the electromagnetic repulsion and have the strong force attraction take place.
Which of the following is a true statement about melting and boiling points in materials made of covalent molecules?
Hydrogen bonding between molecules increases melting and boiling points
Which of the following is unimportant in the determining the characteristics of fatty acids?
Ionic bonds
In an irreversible process, what happens to the overall disorder of the universe?
It increases
If a certain LED (doped semi-conductor) is cooled in liquid nitrogen, the color moves to a higher frequency. What happens to the band gap?
It increases in energy
Which of the following correctly applies the law of increasing disorder to an air conditioner?
It is true that the heat flow from the cold region to the hotter region increases order, but this is made up for by increasing the disorder of energy from another source.
How does a catalyst affect a reaction?
It lowers the activation energy
Which of the following is an ionic compound
MgF2
Which of the following pairs would you expect to be covalently bonded?
S and Br
When you compare saturated with unsaturated fatty acids containing the same number of carbon atoms, what is true?
Saturated fatty acids have more hydrogen atoms.
Locate the elements palladium (Pd, atomic #46) and nickel (Ni, atomic #28) on the periodic table. If Pd is combined with Ni, which of the following characteristics will the product show at room temperature?
Shiny, malleable solid
the gasoline engine of an automobile is considerably less than 100% efficient. This means that not all of the energy in the gasoline is turned into kinetic energy of he car. Which of the following best explains why?
Some of the chemical potential energy in the gasoline must become ambient thermal energy if the rests to supply the kinetic energy of the automobile. Tis means some energy must be wasted.
The next two questions deal with this graph showing nucleon mass versus atomic number. Both fission and fusion can result in a release of energy. Why?
The nuclei of atoms near the middle of the periodic table have the least energy and the nucleons with the smallest mass.
This chart shows electronegativities. What can you conclude about the molecule?
The oxygen will be more negative than the carbon.
A window air conditioner is normally placed in a window so the hot air from the back blows outside. What would happen if the air conditioner were placed in the middle of a closed room and turned on?
The room would heat up because all of the energy absorbed by the air conditioner, both thermal and electrical potential, is released back into the room as thermal energy.
Carbon-14 (14C) is not stable and it spontaneously decays into nitrogen-14 (14N) and an electron by a radioactive beta-decay. Which of the following is true about the decay?
The total number of nucleons stays the same.
What best describes how the oxygen molecules would behave if mixed with water?
They would dissolve poorly or not at all because they are not polar.
In minerals, the underlying atomic structure gives rise to large-scale properties observable with the naked eye.
True
N2 has a triple bond and is a gas at room temperature. The triple bond is a very strong bond.
True
Quartz is a silicate that has strong bonds throughout its entire structure.
True
Unsaturated fats are considered an essential part of a healthy diet.
True
Ionic compounds are formed between a metal and a...
nonmetal
The process that produces most of the explosive energy of a hydrogen bomb and that is believed to be responsible for the energy released by the sun is called
nuclear fusion.
These graphs show energy as a function of time for several different reactions. Which of the reactions shown below would end up absorbing energy from the surroundings?
the one where the energy is more after the reaction than before the reaction
Carbon and oxygen react according to the equation: 6O2 + C6 ⇨ 6CO2. In the diagrams, the lighter balls are carbon, and the darker balls are oxygen. If the reactants in the box react completely, which of the pictures on the right best represents the total products that are formed?
the one with 12 molecules of 2 O to 1 C
Which of the following is a mass spectrum for propylene? (The smallest mass shown is 5.)
the one with small lines at 15 medium lines at 26 and larger more lines at 40
A reversible process does what to the total disorder in the universe?
the total disorder does not change
The purpose of the control rods in a nuclear fission reactor is
to absorb neutrons, thus limiting the number of nuclei undergoing fission.
Energy and entropy are both involved in chemical reactions.
true
Metals have a greater tendency than nonmetals to lose electrons
true
How many more electrons does unbound oxygen need to fill its 2nd shell?
2
The Second Law of Thermodynamics (Law of Increasing Disorder) places limits on the efficiency of energy conversion. Which of the following is allowed?
100% conversion of electricity to ambient temperature thermal energy
In the chemical equation C6H12O6 + 3O2 ⇒ 3CO2 + 6H2O, how many oxygen atoms are on the right side of the equation?
12
When some Ca(NO3)2 dissolves in water, which picture best represents what the solution looks like? (Note, the balls are not meant to indicate charge or lack of charge.)
B: Ca alone N and O bound together
which of the following is atomic matter rather than molecular or network matter?
neon gas
Metals have higher ionization energies than nonmetals do.
False
Mica is a silicate that has strong bonds throughout its entire structure.
False
Molecular orbitals are the same shape as atomic orbitals.
False
Quartz, a mineral with no regular pattern when seen in large quantities, has fibrous layering in its atomic structure.
False
The energies of the orbitals that form when metals interact are very widely spaced in energy.
False
Which of the following fatty acids is best for human health?
Fatty acids that have one or more "bent" cis-double bonds between carbon atoms.
Which of the following would best describe the room temperature characteristics of the substance that results from the reaction between magnesium (Mg) and oxygen (O)?
a brittle, transparent, electrically non-conducting solid
Two or more different elements hat are chemically combined are always what kind of substance?
a compound
Nuclear fission is when
a large nucleus breaks apart into smaller pieces.
Which of the following is a correct comparison of metals and semi-conductors?
a metal's resistance increases when temperature increases while a semi-conductor's resistance decreases.
A metal can best be described as
a network solid consisting of positively charged atoms in a sea of electrons.
Which of the following would best describe the characteristics of the material formed?
a non-conducting material with low melting and boiling points, likely liquid or gas at room temperature.
What is the approximate range of the nuclear strong force? (In other words, what is the distance over which the strong force is significant?)
about the size of a nucleus
What are compounds between two different metals called?
alloys
Which of the following is not why alloys are useful to us today?
alloys have a higher conductivity rate.
Which of the following processes is closest to an ideal reversible process?
an ice cube floating a glass of water at zero degrees
Which of the following is not a characteristic of a metal or alloy?
brittle
Which of the following would best describe the room-temperature characteristics of an ionic substance?
brittle, transparent, electrically non-conducting solid
Which of the following tends to have the highest melting and boiling points?
network matter
Which of the following is not used as a measurement technique for identifying chemical substances?
color spectroscopy
What type of bond would exist between the carbon and the oxygen?
covalent
Entropy is a measure of the ________ of a system.
disorder
In the future, engineers will be able to design a car that is completely efficient.
false
It is possible to predict exactly when a radioactive nucleus will decay.
false
Light can only be seen through very thin metal
false
The forces between the N2 molecules are very strong
false
Complete conversion of one form of energy to another can occur only in which direction?
from higher to lower organized forms
Which of the following set of properties is most likely those associated with methane, a covalently bonded compound?
gas at room temperature, colorless, does not conduct electricity when solid
Which type of energy is the most ordered?
gravitational potential energy
Isotopes of an element are different atoms of the element that
have the same number of protons, but differ in mass number.
What are some characteristics of a metal or alloy?
malleable, thermally conductive, electrically conductive