What is the relationship between absolute pressure, gauge pressure, and atmospheric pressure?
ACS code: AM.I.J
Correct answer: Absolute pressure equals gauge pressure plus atmospheric pressure
Rationale: Gauge pressure is measured relative to ambient atmospheric pressure (a gauge reads zero when open to the atmosphere). To obtain absolute pressure, which is measured from a perfect vacuum, you add the atmospheric pressure to the gauge reading. The handbook's physics chapter defines absolute pressure as gauge pressure plus atmospheric pressure.
According to Boyle's law, if the volume of a confined gas is decreased while temperature is held constant, the pressure of the gas will
ACS code: AM.I.J
Correct answer: increase
Rationale: Boyle's law states that, at constant temperature, the pressure of a confined gas is inversely proportional to its volume (P x V = constant). Reducing the volume forces the same number of gas molecules into a smaller space, so they strike the container walls more often, raising the pressure.
Which statement correctly describes the heat transfer method known as convection?
ACS code: AM.I.J
Correct answer: Heat transfer by the circulation of a heated fluid or gas
Rationale: Convection is the transfer of heat by the movement of a heated fluid or gas; warmer, less dense fluid rises and cooler fluid moves in to replace it, creating circulation. Conduction is transfer through direct contact, and radiation is transfer by electromagnetic waves, so those describe the other two heat-transfer methods.
A first-class lever provides a mechanical advantage when the
ACS code: AM.I.J
Correct answer: effort arm is longer than the resistance arm
Rationale: Mechanical advantage of a lever equals the length of the effort arm divided by the length of the resistance arm. When the effort (force) arm is longer than the resistance arm, the ratio exceeds one, so a smaller applied force can move a larger resistance. Equal arms give a ratio of one (no advantage), and a shorter effort arm gives a ratio less than one.
What does the specific gravity of a substance compare?
ACS code: AM.I.J
Correct answer: The density of the substance to the density of water
Rationale: Specific gravity is the ratio of the density of a substance to the density of pure water, which is the standard reference. Because it is a ratio of two densities, it is a dimensionless number; a value greater than one means the substance is denser than water. Weight divided by volume defines density itself, not specific gravity.
According to Bernoulli's principle, as the velocity of a fluid moving through a tube increases, the static pressure of that fluid
ACS code: AM.I.J
Correct answer: decreases
Rationale: Bernoulli's principle states that within a flowing fluid, an increase in velocity is accompanied by a decrease in static pressure, because the total energy of the flow is conserved. As fluid speeds up through a constriction (a venturi), more of its energy is kinetic and less is in the form of static pressure.
Newton's first law of motion states that a body at rest tends to remain at rest, and a body in motion tends to remain in motion, unless acted upon by
ACS code: AM.I.J
Correct answer: an external force
Rationale: Newton's first law, the law of inertia, states that an object will not change its state of motion unless an unbalanced external force acts on it. Inertia is the property by which the body resists this change; it is not something that is lost, and mass does not spontaneously change, so the external force is the only correct cause.
What happens to most solid materials when they are heated?
ACS code: AM.I.J
Correct answer: They expand
Rationale: When most solids are heated, the increased energy causes their molecules to vibrate more and move farther apart, so the material expands in length, area, and volume. This is why mechanics must account for thermal expansion in fitted parts and why different metals with different expansion rates can loosen or bind when temperatures change.
On the Fahrenheit temperature scale, water at standard atmospheric pressure boils at
ACS code: AM.I.J
Correct answer: 212 degrees
Rationale: On the Fahrenheit scale at standard sea-level atmospheric pressure, water freezes at 32 degrees and boils at 212 degrees, giving 180 degrees between the two points. The 100-degree value is the boiling point on the Celsius scale, and 32 degrees Fahrenheit is the freezing point of water, not its boiling point.
Power is best defined as the
ACS code: AM.I.J
Correct answer: rate at which work is done
Rationale: Power is the time rate of doing work, calculated as work divided by the time required to do it. Two machines can perform the same total work, but the one that does it in less time develops more power. Force alone and total work are separate quantities that do not include the element of time.
An atom with three electrons in its outer shell is said to be
ACS code: AM.I.J
Correct answer: trivalent.
Rationale: An atom's valency is set by the number of electrons in its outer (valence) shell. With three electrons available to form bonds, the atom is described as trivalent. Two electrons would make it divalent and one would make it univalent. FAA-H-8083-30 covers the physics of matter and atomic structure.
What is the mass number of an element?
ACS code: AM.I.J
Correct answer: The number of protons and neutrons.
Rationale: The mass number counts the nucleons in the nucleus, which are the protons plus the neutrons. Electrons are far too light to contribute meaningfully and are not counted. FAA-H-8083-30 covers atomic structure and the physics of matter.
What is formed when two molecules of hydrogen combine with one molecule of oxygen?
ACS code: AM.I.J
Correct answer: Two molecules of water (2H2O).
Rationale: Combining two hydrogen molecules with one oxygen molecule forms two water molecules, written 2H2O. Each water molecule is built from two hydrogen atoms bonded to one oxygen atom. FAA-H-8083-30 covers basic chemistry and the physics of matter.
Breaking a chemical compound down into its constituent elements is called
ACS code: AM.I.J
Correct answer: analysis.
Rationale: Breaking a compound down into its constituent elements is termed analysis, the opposite of synthesis where elements combine. This separates the compound into simpler parts rather than forming anything new. FAA-H-8083-30 covers basic chemistry and the physics of matter.
What is the atomic number of an element?
ACS code: AM.I.J
Correct answer: The number of protons in the atom.
Rationale: The atomic number equals the number of protons in the nucleus, and it uniquely fixes which element the atom is. Neutron count varies between isotopes and electron count varies with ionization, so only the proton number defines the atomic number. FAA-H-8083-30 covers atomic structure.
An atom consists of
ACS code: AM.I.J
Correct answer: protons, neutrons, and electrons.
Rationale: An atom is built from a nucleus of protons and neutrons surrounded by orbiting electrons. Photons and positrons are not structural components of an ordinary atom. FAA-H-8083-30 covers atomic structure and the physics of matter.
The maximum number of electrons in the innermost shell of an atom is
ACS code: AM.I.J
Correct answer: 2.
Rationale: The innermost (K) shell can hold a maximum of two electrons. Only from the second shell onward can a shell accommodate eight, so two is the correct limit for the inner shell. FAA-H-8083-30 covers atomic structure and electron shells.
The mass of a proton is approximately equal to the mass of a
ACS code: AM.I.J
Correct answer: neutron.
Rationale: A proton and a neutron have almost identical masses, each about one atomic mass unit, with the neutron only marginally heavier. The electron is roughly 1,800 times lighter. FAA-H-8083-30 covers atomic structure and the physics of matter.
When the outer shell of an atom is full, the element is
ACS code: AM.I.J
Correct answer: practically inert.
Rationale: An atom whose outer shell is full has no tendency to gain, lose, or share electrons, so it does not readily react or conduct. This stable configuration is why the noble gases are practically inert. FAA-H-8083-30 covers atomic structure and electron shells.
The attractive force that holds together molecules of the same compound is called
ACS code: AM.I.J
Correct answer: cohesion.
Rationale: Attraction between molecules of the same substance is called cohesion, which holds like molecules together. Adhesion describes attraction between unlike materials. FAA-H-8083-30 covers the physics of matter, including cohesion and adhesion.
Oxygen has a valency of
ACS code: AM.I.J
Correct answer: 2.
Rationale: Oxygen needs two electrons to complete its outer shell, giving it a valency of two. This is why it bonds with two hydrogen atoms to form water, H2O. FAA-H-8083-30 covers basic chemistry and atomic structure.
As the electron shells in an atom get further from the nucleus, the spacing between successive shells
ACS code: AM.I.J
Correct answer: increases, so the shells get further apart.
Rationale: As electron shells extend outward from the nucleus, the spacing between successive shells increases. The shells get further apart with distance rather than collapsing or crowding together. FAA-H-8083-30 covers atomic structure and electron shells.
What determines an element's identity?
ACS code: AM.I.J
Correct answer: The number of protons.
Rationale: An element's identity is determined solely by its proton count, the atomic number. Changing neutrons only produces a different isotope of the same element, and changing electrons only produces an ion. FAA-H-8083-30 covers atomic structure.
An isotope of an element has a different number of _________ than the common form.
ACS code: AM.I.J
Correct answer: neutrons
Rationale: Isotopes of an element share the same number of protons but differ in their number of neutrons. An isotope therefore has more or fewer neutrons than the common form, which is why its mass differs while its chemical identity does not. FAA-H-8083-30 covers atomic structure and isotopes.
The smallest part of an element that still retains the chemical properties of that element is
ACS code: AM.I.J
Correct answer: an atom.
Rationale: The atom is the smallest particle of an element that still retains the chemical properties of that element. Subatomic particles such as quarks and mesons no longer behave as the element, so the atom is correct.
The nucleus of an atom contains
ACS code: AM.I.J
Correct answer: protons and neutrons.
Rationale: The nucleus holds the protons and neutrons, which together account for nearly all of the atom's mass. Electrons orbit outside the nucleus rather than residing within it, so options placing electrons in the nucleus are wrong.
The atomic mass of an atom is the
ACS code: AM.I.J
Correct answer: number of protons plus the number of neutrons.
Rationale: Atomic mass is the sum of the nucleons in the nucleus, the protons plus the neutrons. Electrons are too light to add appreciably to the mass, so they are not included in the count.
When ice melts into liquid water, the resulting water takes up
ACS code: AM.I.J
Correct answer: less space.
Rationale: Water is unusual in that ice is less dense than liquid water because the open crystal structure of ice expands its volume. When ice melts, that structure collapses and the resulting water takes up less space.
Which form of heat is absorbed to change a solid into a liquid?
ACS code: AM.I.J
Correct answer: Heat of fusion.
Rationale: Changing a solid into a liquid requires the latent heat of fusion, the energy absorbed to break the bonds of the solid structure while the temperature stays constant. This is the heat added during melting.
A change of state directly from a solid to a gas, without passing through the liquid state, is called
ACS code: AM.I.J
Correct answer: sublimation.
Rationale: Sublimation is the direct change of a substance from solid to gas without passing through the liquid phase. Evaporation involves a liquid surface, so it does not describe this solid-to-gas transition.
A positive ion is an atom that
ACS code: AM.I.J
Correct answer: is missing one or more electrons.
Rationale: A positive ion forms when an atom loses one or more electrons, leaving more protons than electrons and an overall positive charge. Gaining electrons instead would create a negatively charged ion.
Carbon-14 and carbon-12 are isotopes of carbon, so both atoms have the same
ACS code: AM.I.J
Correct answer: number of protons.
Rationale: Carbon-14 and carbon-12 are isotopes of the same element, so they share the same number of protons. They differ only in neutron count, which gives them different mass numbers while keeping them both carbon.
If a neutral atom has 2 protons, how many electrons does it have?
ACS code: AM.I.J
Correct answer: 2.
Rationale: A neutral atom has equal numbers of protons and electrons so that the charges balance. With two protons it therefore has two electrons, identifying the atom as helium.
A molecule made up entirely of identical atoms is a molecule of
ACS code: AM.I.J
Correct answer: an element.
Rationale: A molecule made up of identical atoms is a molecule of an element, since only one type of atom is present. A compound, by contrast, requires two or more different kinds of atom.
Two or more different elements chemically combined in a single substance form a
ACS code: AM.I.J
Correct answer: compound.
Rationale: When two or more different elements are chemically combined in a single substance, the result is a compound. A mixture does not chemically bond the elements, so compound is the correct term.
In a neutral atom, the number of protons is equal to the number of
ACS code: AM.I.J
Correct answer: electrons.
Rationale: In a neutral atom the positive and negative charges balance, so the number of protons equals the number of electrons. Positrons and molecules play no part in this balance.
The electrical charge carried by an electron is
ACS code: AM.I.J
Correct answer: negative.
Rationale: The electron carries a single negative charge, balancing the positive charge of the proton. The neutron is uncharged, so neither positive nor neutral describes the electron.
A valence electron is an electron located
ACS code: AM.I.J
Correct answer: in the outermost shell.
Rationale: A valence electron is one occupying the outermost shell of an atom. These outer electrons govern how the atom bonds and reacts, which is why inner-shell electrons are not valence electrons.
The attractive force that holds together molecules of unlike substances is called
ACS code: AM.I.J
Correct answer: adhesion.
Rationale: When unlike atoms or molecules are joined, the attraction between the dissimilar particles is termed adhesion. Cohesion applies to attraction between like molecules of the same substance, so adhesion is correct here.
Hydrogen, deuterium, and tritium are isotopes of hydrogen that differ from one another in the number of
ACS code: AM.I.J
Correct answer: neutrons.
Rationale: Hydrogen, deuterium, and tritium are isotopes of hydrogen, all with one proton and one electron. They differ only in their neutron count, having zero, one, and two neutrons respectively.
Anything that has mass and occupies space, whether solid, liquid, or gas, is defined as
ACS code: AM.I.J
Correct answer: matter.
Rationale: Anything that has mass and occupies space, whether solid, liquid, or gas, is defined as matter. Energy has no mass or volume of its own, and volume is only a measure of the space occupied, so matter is correct.
An atom is made up of which three basic particles?
ACS code: AM.I.J
Correct answer: Protons, neutrons, and electrons.
Rationale: All matter is composed of atoms, and every atom is built from protons and neutrons in a central nucleus with electrons orbiting around it. Positrons are not part of ordinary atomic structure, so any choice that lists them is incorrect.
The force of molecular attraction between two unlike substances is called
ACS code: AM.I.J
Correct answer: adhesion.
Rationale: Adhesion is the attraction between molecules of two different (unlike) substances, such as a liquid clinging to a surface. Cohesion is the attraction between molecules of the same substance, so the force acting between unlike substances is adhesion.
Which form of heat is absorbed when a substance changes directly from a solid to a gas?
ACS code: AM.I.J
Correct answer: Latent heat.
Rationale: Latent heat is absorbed during a change of state without any change in temperature, including the direct solid-to-gas change called sublimation. The energy goes into breaking the bonds between molecules rather than raising the temperature.
The heat required to change a liquid to a gas at constant temperature is the latent heat of
ACS code: AM.I.J
Correct answer: vaporization.
Rationale: The latent heat of vaporization is the energy required to change a liquid into a gas at a constant temperature. Condensation is the reverse process (gas to liquid) and fusion applies to melting, so vaporization is the correct term.
A substance made of two or more different elements that are chemically bonded together is
ACS code: AM.I.J
Correct answer: a compound.
Rationale: A compound is formed when two or more different elements are chemically bonded together in fixed proportions, producing a substance with new properties. A mixture involves no chemical bonding, so compound is the correct description.
The smallest particle of an element that still retains the properties of that element is
ACS code: AM.I.J
Correct answer: an atom.
Rationale: The atom is the smallest particle of an element that retains the element's identity and cannot be subdivided by ordinary chemical means. A molecule is a combination of atoms, and a compound is a substance of bonded elements, so the atom is the correct unit.
A compound is best described as a substance in which two or more elements are
ACS code: AM.I.J
Correct answer: chemically bonded together to form a new material.
Rationale: A compound is formed when two or more elements are chemically bonded together in fixed proportions, producing a substance with new properties. Merely mixing elements physically gives a mixture, not a compound, because no chemical bond is created.
In how many physical states can a substance such as water exist?
ACS code: AM.I.J
Correct answer: Three.
Rationale: Water can exist in three common states of matter: solid (ice), liquid (water), and gas (steam or water vapor). The state depends on temperature and pressure, and water changes between all three without altering its chemical composition.
One newton of force is equal to
ACS code: AM.I.J
Correct answer: one kilogram-meter per second per second.
Rationale: By Newton's second law (force = mass x acceleration), one newton is the force that accelerates a one-kilogram mass at one meter per second squared, so 1 N = 1 kg·m/s². Force uses kilograms of mass and meters, not kilograms-force or grams and centimeters.