PHYS 100 - exam 3
In the equation C2H4 + 3O2 = ? CO2 + 2H2O, how many CO2 molecules are needed to balance the equation?
2
A metal can best be described as
a network solid consisting of positively charged atoms in a sea of electrons.
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
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
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
Pure aluminum metal has a melting temperature at 660 ˚C. The process of liquid aluminum freezing to solid aluminum at this temperature is
reversible
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
Which is the best definition of an alloy?
solid mixture of metals
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.
The oxidation state of an atom refers to
the number of electrons gained or lost when an ionic bond is formed.
N2 has a triple bond and is a gas at room temperature. The triple bond is a very strong bond.
true
It is energetically favorable for non-metals to share electrons.
true Because of their strong attraction for electrons, non-metals are attracted to the electrons of other atoms.
Non-metal nuclei have a strong attraction for valence electrons.
true The high ionization energy of non-metals is evidence for a strong electron-nuclear attraction.
To form a positive ion with a noble gas configuration (ns2np6) from a non-metal requires a tremendous amount of energy.
true To form a positively charged ion with a noble gas configuration from a non-metal means that up to seven valence s and p electrons may need to be removed. Since the ionization energy of each valence electron is high, the cost to remove that many would be exorbitant.
In an irreversible process, what happens to the overall disorder of the universe?
It increases.
When does the system have more order?
before the separator is removed
The various forms of energy can be ranked according to their level of what?
organization
If the two figures represent snapshots in time of an irreversible process, which figure came first and why?
Figure 18.2 because molecules rush inside the box to get rid of the vacuum.
Which of the following tends to have the highest melting and boiling points?
network matter
Which type of atom has the highest ionization energy?
non-metal
We see a large amount of order in the world around us from life to currents in the air and ocean. How is this consistent with the law of increasing disorder?
It is because the sun provides additional high-order energy to the world to create this order.
An air conditioner causes a cool place (the inside of your house) to become colder, but at the same time heats up a warmer space. (An air conditioner blows hot air out the back, heating up the outside air even more). 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.
Magnesium chloride forms a solid in which two chloride ions are found for every magnesium ion but no discrete molecules are observed in the solid. What is the simplest formula for this compound?
MgCl2
Which of the following is an ionic compound?
MgF2
What classification of matter is magnesium chloride?
Network Matter
Hydrogen (H2) and oxygen (O2) react to produce water (H2O). The unbalanced equation is as shown: H2 + O2 → H2O Are the hydrogen atoms still balanced? H2 + O2 → 2H2O
No
Hydrogen (H2) and oxygen (O2) react to produce water (H2O). The unbalanced equation is as shown: H2 + O2 → H2O Are the oxygen atoms balanced?
No
What happens to the valence electrons as the product (MgO) is formed?
The magnesium atoms' valence electrons are effectively transferred to oxygen.
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
Which of the following is atomic matter rather than molecular or network matter?
neon gas
Non-metals have a large number of s and p-type valence electrons relative to metals.
true non-metals have between 4 and 7 of these kind of electrons, metals have only 1-3
Hydrogen (H2) and oxygen (O2) react to produce water (H2O). The unbalanced equation is as shown: H2 + O2 → H2O Are the hydrogen atoms balanced?
yes
Hydrogen (H2) and oxygen (O2) react to produce water (H2O). The unbalanced equation is as shown: H2 + O2 → H2O Is the equation balanced now? 2H2 + O2 → 2H2O
yes
In the chemical equation C6H12O6 + 3O2 ⇒ 3CO2 + 6H2O, how many oxygen atoms are on the right side of the equation?
12
In which of the following processes is the end product more ordered than the reactants? (In which process does entropy decrease in the system?) NaHCO3 (solid) + C2H4O2 (liquid)=C2H3NaO2 (solid)+ H2O(liquid) + CO2 (gas) 2C8H18 (liquid) + 25O2 (gas) = 16CO2 (gas) + 18H2O (gas) 2C7H5N3O6 (solid) = 3N2 (gas) + 7CO(gas) + 5H2O (gas) + 7 C (solid) 2H2 (gas) + O2 (gas) = 2 H2O (gas) C6H12O6 (solid) + 6O2 (gas) = 6CO2 (gas) + 6H2O (liquid)
2H2 (gas) + O2 (gas) = 2 H2O (gas)
In the future, engineers will be able to design a car that is completely efficient.
False
What is the charge of iron (Fe) in the compound Fe2O3?
+3
bonds arise from electrostatic interactions in. 1. covalent 2. ionic 3. metallic
1. true 2. true 3. true
Each molecule of methane has the formula CH4. If there are 4000 carbon atoms present, how many hydrogen atoms will be required to convert all of the carbon atoms into methane?
16,000
How many more electrons does unbound oxygen need to fill its 2nd shell? (You may find it helpful to draw the energy well on scratch paper.)
2
How many bonds does each carbon have in propanol?
4
In acetaldehyde, how many of each type of bond are there?
5 Single, 1 Double, 0 Triple
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.
If GaAs forms a semiconductor like Ge, which of the following elements will form a semiconductor like Si? (Hint: look at the periodic table.)
Al and P
Characterize the following reactions as occurring with a favorable energy change for the system, a favorable entropy change for the system, or both. Remember, gases have more disorder than liquids which have more disorder than solids. H2 (gas) + O2 (gas) ⇒ H2O (gas), energy is given off:
BOTH This is an interesting situation because the product is actually more ordered than the reactants, meaning there is more order in the system after the reactions takes place. H2O is a specific arrangement of two elements as opposed to two separate elements so H2O is more ordered. The overall disorder of the universe increases, however, because of the large amount of thermal energy that is released. Remember from Lesson 18 that thermal energy is more disordered than chemical energy
What is the chemical formula for acetaldehyde?
C2H4O
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.
On paper, draw a ball and stick diagram for the next family member in the aldehyde family after propanal. Which of the following diagrams best represents this next member of the aldehyde family?
D
According to the molecular model of matter, increasing the temperature of a gas increases the average speed of the gas molecules. Does increasing the temperature of the gas increase or decrease the disorder of the gas? To answer the question, use activity 18.3. You can change the temperature of one of the gases. Which appears more chaotic, the gas with the higher temperature or the lower temperature?
Disorder is greater when the temperature is higher.
A car can't convert all of the energy from its fuel to macroscopic kinetic energy. Why?
Entropy would decrease. Converting the chemical potential energy of the gasoline into macroscopic kinetic energy represents an increase in order (decrease in entropy). This would violate the Law of Increasing Disorder so some of the chemical potential energy must be converted into thermal energy.
Current can flow in all directions in an LED
FALSE
Metals have higher ionization energies than nonmetals do.
FALSE
The energies of the orbitals that form when metals interact are very widely spaced in energy.
FALSE
A very fast reaction has a very high activation energy.
False
Dispersion forces are stronger than covalent bonds.
False
Hydrogen (H2) and oxygen (O2) react to produce water (H2O). The unbalanced equation is as shown: H2 + O2 → H2O Could you balance the oxygen atoms by changing H2O to H2O2?
No would make it a different compound
Can sulfur be considered a compound and why?
No, it is composed of only one type of atom.
Which of the following pairs would you expect to be covalently bonded?
S and Br
What is the chemical formula for sulfur?
S8
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 the car. Which of the following best explains why?
Some of the chemical potential energy in the gasoline must become ambient thermal energy if the rest is to supply the kinetic energy of the automobile. This means some energy must be wasted.
Metals have a greater tendency than nonmetals to lose electrons.
TRUE
What happens to the number of molecular orbitals as the number of atoms that come together increases?
The number of molecular orbitals increases.
A perfume bottle drops and shatters on the floor of a room. (An irreversible process has just occurred-the breaking of the bottle!) You observe that you can smell the perfume throughout the entire room a few seconds later. Which of the following explanations of this observation is correct?
The perfume's odor is caused by its molecules. Molecules of perfume in the liquid are in random motion. When the bottle breaks, the molecules can vaporize and spread throughout the room, mixing with the air in the room. The room with perfume molecules spread around it is more disordered than with them concentrated in a spot surrounding the broken bottle.
An air conditioner causes a cool place (the inside of your house) to become colder, but at the same time heats up a warmer space. (An air conditioner blows hot air out the back, heating up the outside air even more). 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.
What happens to the spacing between the energy of one molecular orbital and the next one immediately above or below it as the number of atoms that come together increases?
The spacing between energy levels decreases.
A reversible process does what to the total disorder in the universe?
The total disorder does not change.
Energy and entropy are both involved in chemical reactions.
True
Hydrogen (H2) and oxygen (O2) react to produce water (H2O). The unbalanced equation is as shown: H2 + O2 → H2O Are oxygen atoms balanced if a 2 is placed in front of water to make the following equation?: H2 + O2 → 2H2O
Yes The factor of two in front means two water molecules. Since each water molecule contains one oxygen atom, there is now a total of two oxygen atoms on the right side of the equation.
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 that are chemically combined are always what kind of substance?
a compound
C3H8 (gas) + 5O2 (gas)⇒ 3CO2 (gas) + 4H2O (liquid), energy given off:
both
Which of the following is not used as a measurement technique for identifying chemical substances?
color spectroscopy THAT ARE USED: - vibrational spectroscopy - crystallography - mass spectroscopy - electronic spectroscopy
Which of the following substances is most likely to be a pure element?
copper
Entropy is a measure of the ________ of a system.
disorder
The forces between the N2 molecules are very strong.
false
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
How does a catalyst affect a reaction?
it lowers the activation energy
Which type of atom has valence electron states high enough in energy that they overlap with the stacked-together molecular orbitals that form the conduction band?
metal
C6H12O6 (solid) + 3O2 (gas) ⇒ 3CO2 (gas) + 6H2O (liquid), energy given off:
both
Molecular orbitals are the same shape as atomic orbitals.
False
Which type of atom has valence electrons higher in the energy well?
metal
Which type of energy is the most ordered?
gravitational potential energy
Rank the following according to their strength, weakest first, strongest last.
dispersion forces, dipole-dipole interactions, hydrogen bonding, covalent bonding
A valence electron in a non-metal has a very low ionization energy.
false As one goes from left to right across a period, the first ionization energy increases Non-metals are on the right side of the periodic table, so they have high first ionization energies.
Light can only be seen through very thin metal.
false - metals are opaque
NH4NO3 (solid) + H2O (liquid) ⇒ NH4+ + NO3- in water solution, energy absorbed:
favorable entropy change
Complete conversion of one form of energy to another can occur only in which direction?
from higher to lower organized forms
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 in a glass of water at zero degrees
Which of the following is not a characteristic of a metal or alloy?
brittle WHAT ARE CHARACTERISTICS: malleable electrically conductive thermally conductive
Which of the following would best describe the room-temperature characteristics of an ionic substance?
brittle, transparent, electrically non-conducting solid
Consider a refrigerator and its contents to be the system. Warm food is cooled to a lower temperature. Warm water is cooled in the freezer and eventually frozen to ice. Do these two processes, cooling food and freezing water, increase the entropy inside the refrigerator?
No Lowering the temperature reduces entropy or disorder.
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
An ice cube melts in a glass of warm water. This is an example of which type of process?
irreversible
Ionic compounds are formed between a metal and a
nonmetal
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?
one with the end higher than it starts
What happens to the valence electrons as an ionic compound if formed?
The metal atoms' valence electrons are effectively transferred to the nonmetal.