Exam 3 Practice - Pre-AP Chem

Explanation
The molecules in both liquid and gas states of matter are able to take the shape of their container. In a liquid, the molecules are closely packed but still have the ability to move around and flow, allowing them to conform to the shape of the container. In a gas, the molecules are much more spread out and move freely, filling the entire container and taking its shape. Therefore, both liquid and gas states exhibit this property of taking the shape of their container.

Explanation
According to the kinetic-molecular theory, particles of matter are in motion at all temperatures above absolute zero. This theory states that all particles, whether in gases, liquids, or solids, are in constant motion. At absolute zero, the lowest possible temperature, particles theoretically have no kinetic energy and therefore no motion. However, as the temperature increases, the particles gain kinetic energy and move more rapidly. Therefore, the correct answer is that particles of matter are in motion at all temperatures above absolute zero.

Explanation
Evangelista Torricelli invented the barometer, an instrument used to measure atmospheric pressure. A barometer works by balancing the weight of the atmosphere with the weight of a column of mercury or other liquid. By measuring the height of the liquid column, the atmospheric pressure can be determined. A manometer is a similar instrument used to measure pressure, but it is typically used for measuring the pressure of gases or liquids in closed systems. A U-tube is a type of manometer that uses a U-shaped tube filled with liquid to measure pressure differentials. A torrometer is not a known instrument for measuring atmospheric pressure.

Explanation
The correct answer is 245 kPa because to convert from atmospheres to kilopascals, you need to multiply the pressure in atmospheres by the conversion factor of 101.3 kPa/1 atm. Therefore, 2.42 atmospheres multiplied by 101.3 kPa/1 atm equals 245 kPa.

Explanation
The given question asks for the number of moles in a given number of atoms of W. The answer 4.65 mol is obtained by dividing the given number of atoms (2.8 x 10^24) by Avogadro's number (6.022 x 10^23), which represents the number of atoms in one mole of a substance. This calculation gives the result of approximately 4.65 mol.

Explanation
One mole of BaCl2 refers to the molar mass of BaCl2, which is the sum of the atomic masses of one barium atom (Ba) and two chlorine atoms (Cl). The atomic mass of barium is 137.3 g/mol, and the atomic mass of chlorine is 35.5 g/mol. Adding these values together gives a molar mass of BaCl2 equal to 208.3 g/mol. Therefore, the correct answer is 208.3 g.

Explanation
The number of moles in a substance can be calculated using the formula: moles = mass / molar mass. In this case, the molar mass of Ba(NO3)2 can be calculated by adding up the atomic masses of each element: 137.33 (Ba) + 2(14.01) (N) + 6(16.00) (O) = 261.33 g/mol. Therefore, the number of moles in 432 grams of Ba(NO3)2 would be 432 g / 261.33 g/mol = 1.65 mol.

Explanation
Group 18 of the Periodic Table, also known as the noble gases, tends to have the highest ionization energy. This is because noble gases have a full outer electron shell, making them stable and less likely to lose or gain electrons. As a result, it requires a significant amount of energy to remove an electron from a noble gas atom, leading to a high ionization energy.

Explanation
The first ionization energy is the energy required to remove one electron from a neutral atom in its gaseous state. Beryllium is a metal located in Group 2 of the periodic table, and it has two valence electrons. As we move across a period from left to right, the atomic radius decreases, resulting in a stronger attraction between the nucleus and the valence electrons. This increased attraction requires more energy to remove an electron, so the first ionization energy increases. Therefore, the correct answer is 899 kJ/mol, which is the highest value among the given options and indicates the greatest energy required to remove an electron from beryllium.

Explanation
Sr+ does not have an octet because it is a cation with a charge of +1. It loses two electrons from its valence shell, leaving it with only 8 valence electrons instead of the usual 8 electrons needed for an octet.

Explanation
Calcium is in Group 2 of the periodic table, which means it has 2 valence electrons. In order to achieve an octet (8 electrons) in its outermost energy level, calcium can lose these 2 valence electrons. By losing 2 electrons, calcium will have a full outermost energy level, making it more stable. This is the most common way for calcium to achieve an octet of electrons.

Explanation
Oxygen (O) has the highest electronegativity value among the given elements. Electronegativity is a measure of an atom's ability to attract electrons towards itself in a chemical bond. Oxygen is highly electronegative because it has a strong attraction for electrons due to its high effective nuclear charge and small atomic size. This makes oxygen more likely to gain electrons and form negative ions in chemical reactions. In comparison, Francium (Fr) has the lowest electronegativity value as it has a larger atomic size and lower effective nuclear charge, resulting in a weaker attraction for electrons.

Explanation
Oxygen is found in Group 16 of the periodic table, which means it has 6 valence electrons. Valence electrons are the electrons in the outermost energy level of an atom and are responsible for the atom's chemical properties. Therefore, an atom of oxygen would have 6 valence electrons.

Explanation
One mole of any substance contains Avogadro's number of particles, which is approximately 6.022 x 10^23. In the case of water, one mole of water molecules would contain this enormous number of molecules. However, the size of the molecules themselves is very small, so even though there are a huge number of them, they would still fit into a small shot glass.

Explanation
Manometers per square foot could not be a unit of pressure because manometers are devices used to measure pressure, not units of pressure themselves. The correct unit of pressure is typically expressed in terms of force per unit area, such as newtons per square meter (N/m²), pounds per square inch (psi), or pascal (Pa).