PHY S 100 Exam 3

Which of the following would best describe the room-temperature characteristics of an ionic substance?

Brittle, transparent, electrically non-conducting solid.

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.

How does a catalyst affect a reaction?

It lowers the activation energy

Entropy is a measure of the ________ of a system.

disorder

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

Chemical equation

shorthand notation for describing a chemical reaction.

T/F Energy and entropy are both involved in chemical reactions.

true

T/F Metals have a greater tendency than nonmetals to lose electrons.

true

A reversible process does what to the total disorder in the universe?

The total disorder does not change

An energy diagram for the magnesium-oxygen reaction is shown below. 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 below? (The curve for magnesium + oxygen is shown in light grey for reference.)

Twin hills, oxygen higher, cross at the energy level

Second Law of Thermodynamics

see Law of Increasing Disorder.

Blend/composite

solid mixture of compounds.

Which is the best definition of an alloy?

solid mixture of metals

Network matter

substances where every atom interacts strongly with many of their neighbors. An extended network of linked atoms or ions form.

Molecular matter

substances where the elements have strong interactions between a set number of elements so molecules are formed but there are weak interactions outside of the individual molecules.

Reflectivity

the characteristic of being capable of or producing reflection.

Malleability

the characteristic of substances that allows them to be worked into desired shapes or drawn out into wires. It is the opposite of being brittle.

Universe

the combination of the system plus surroundings.

Equilibrium

the condition where the forward rate and reverse rate of a chemical reaction are the same so there is no net change in the system. Energy is a minimum and entropy is a maximum.

Transition state

the critical point that separates reactants from the products on a potential energy surface.

Band gap

the energy difference between the top of the valence band and the bottom of the conduction band in semiconductors.

Activation energy

the energy needed to allow a reaction to occur, to break the bonds of the reactants, and allow the product to form.

What is the best description of activation energy?

the energy that must be put into a system before a reaction can take place.

Activation entropy

the entropy that is associated with the formation of the transition state.

Metallic luster

the high reflectivity or shininess of metals.

Products

the material(s) produced in a chemical reaction, written on the right-hand side of the chemical equation.

Wavenumber

the number of wavelengths in a particular length such as centimeters or meters (1/wavelength). You do not need to know this definition for any exam in this course.

What is the formula for ethene?

C2H4

The chemical formula of the next family member after butylene will have what chemical formula?

CH2CHCH2CH2CH3 (also written C5H10)

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.

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.

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.

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. 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

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.

Efficiency

the percent of energy that is converted into useful energy.

Chemical reaction rate

the speed at which the reactants are consumed and the products are formed.

Reactants

the starting material(s) of a chemical reaction, written on the left-hand side of the chemical equation.

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

Bond

attractive interaction between atoms.

Which of the following is not a characteristic of a metal or alloy?

brittle

Pure substance

matter that has a defined, unchanging, chemical composition.

Bonding molecular orbital

molecular orbitals that have a high probability of finding electrons between the atoms' nuclei. A bond is likely to form with this orbital.

Anti-bonding molecular orbital

molecular orbitals that have a low probability of finding electrons between the atoms' nuclei. A bond is unlikely to form with this orbital.

Ionic compounds are formed between a metal and a

non-metal

What is not used as a measurement technique for identifying chemical substances?

color spectroscopy

Which of the following substances is most likely to be a pure element?

copper

Single bond

covalent bond involving one pair of electrons (2 electrons) shared between two atoms. It is represented by a single line (-).

Double bond

covalent bond involving two pairs of electrons (4 electrons) shared between two atoms. It is represented by a double line (=).

The various forms of energy can be ranked according to their level of what?

organization

Atomic matter

pure substances, such as noble gases (Group 8A), that exist as individual atoms with little or no interaction between the individual atoms themselves.

What is the charge of iron (Fe) in the compound Fe2O3?

+3

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

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

In the equation C2H4 + 3O2 = ? CO2 + 2H2O, how many CO2 molecules are needed to balance the equation?

2

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

why are alloys useful to us today?

Alloys are less malleable. Alloys reduce weight in objects. Alloys have lower melting temperatures.

Which of the following is an ionic compound? O2 NH3 MgF2 CO2

MgF2

What are compounds between two different metals called?

alloys

Which of the following processes is closest to an ideal reversible process?

an ice cube floating in a glass of water at zero degrees

Molecular orbital

an orbital (standing waves describing the probability of finding an electron) around the two or more nuclei which comprise the molecule in question.

What are used as measurement techniques for identifying chemical substances?

electronic spectroscopy vibrational spectroscopy crystallography mass spectroscopy

Surroundings

everything outside of what we have defined to be the system.

T/F A very fast reaction has a very high activation energy.

false

T/F Light can only be seen through very thin metal.

false

T/F Metals have higher ionization energies than nonmetals do.

false

T/F Molecular orbitals are the same shape as atomic orbitals.

false

T/F The energies of the orbitals that form when metals interact are very widely spaced in energy.

false

Complete conversion of one form of energy to another can occur only in which direction?

from higher to lower organized forms

Which type of energy is the most ordered?

gravitational potential energy

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

Will the end of the graph be higher or lower than the beginning if the reaction absorbed energy?

it will be higher than the start

Mixture

matter that contains multiple substances. These substances can be physically separated into their pure substances.

Element

matter that contains only one kind of atom.

Compound

matter that contains two or more kinds of atoms in a fixed and definite proportion.

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)?

Brittle, transparent, electrically non-conducting solid.

T/F In the future, engineers will be able to design a car that is completely efficient.

False

What tends to have the highest melting and boiling points?

network matter

Opacity

Visible light is absorbed. It is the opposite of being transparent.

Catalyst

a chemical which speeds up a reaction without being destroyed or consumed by the reaction.

Alloy

a combination of two or more metals into a single homogeneous substance.

Two or more different elements that are chemically combined are always what kind of substance?

a compound

Potential energy surface

a diagram plotting the total energy of the reactants and products as chemical reaction occurs.

Electrical conductivity

a measure of the degree to which a substance conducts electricity.

Thermal conductivity

a measure of the degree to which a substance conducts heat.

Solution

a mixture containing at least two compounds with at least one of the compounds in liquid form.

Entropy

a quantitative measure of disorder. It increases as disorder increases.

Law of Increasing Disorder

a reversible process does not change the total amount of disorder in the universe. An irreversible process increases the total amount of disorder in the universe.

N-type semiconductor

a semiconductor with extra electrons in the valence band. It is formed by adding a different semiconductor, such as phosphorus, to the host semiconductor.

P-type semiconductor

a semiconductor with vacancies in the conduction band. It is formed by adding a different semiconductor, such as aluminum, to the host semiconductor.

System

a small piece of the world around which we draw a mental box and upon which we focus our attention.

Atomic orbital

an orbital (standing waves describing the probability of finding an electron) which is associated with a single atomic nucleus.

Salt

at least one metal and non-metal bonded together to form network matter.

Which of the following is atomic matter rather than molecular or network matter?

neon gas