HESI A2 Chemistry Practice Questions

Correct Answer: A

Rationale: Step-by-step rationale: 1. Heating increases kinetic energy of particles. 2. Higher kinetic energy results in faster movement. 3. Faster movement leads to increased collisions. 4. Increased collisions enhance diffusion rate. Summary of incorrect choices: B. Space between particles increasing doesn't directly affect diffusion rate. C. Density of particles decreasing doesn't necessarily impact diffusion rate. D. Size of particles increasing doesn't affect diffusion rate directly.

Correct Answer: C

Rationale: The correct answer is C: metalloids. Arsenic and silicon are classified as metalloids due to their properties that are intermediate between metals and nonmetals. Metalloids have characteristics of both metals and nonmetals, such as varying conductivity, reactivity, and physical appearance. Arsenic and silicon exhibit this behavior, making them suitable examples of metalloids. Incorrect Answers: A: Metals - Arsenic and silicon do not exhibit typical metallic properties such as high electrical conductivity and luster. B: Nonmetals - While silicon can exhibit nonmetallic properties, arsenic does not fit the characteristics of a nonmetal. D: Heavy metals - Heavy metals typically refer to metals with high atomic weights, which is not the defining characteristic of arsenic and silicon.

Correct Answer: D

Rationale: The correct answer is D: column. Elements in the same column of the periodic table, also known as groups, have similar properties due to the same number of valence electrons. This similarity is a result of the elements' electronic configuration, leading to comparable chemical behavior. In contrast, rows (choice A) represent periods, indicating elements with increasing atomic numbers but not necessarily similar properties. Principal energy levels (choice B) are related to the energy levels of electrons in an atom, not the grouping of elements. Choice C, period, refers to elements arranged horizontally on the periodic table, which do not share the same properties as elements in the same column.

Correct Answer: B

Rationale: To balance the equation Fe + Cl2 → FeCl3, we need to ensure the same number of each type of atom on both sides. Starting with Fe, we have 1 Fe on the left and 1 Fe on the right, so Fe is balanced. Next, we have 2 Cl on the left from Cl2 and 3 Cl on the right from FeCl3. To balance Cl, we need to multiply Cl2 by 3 to get 6 Cl atoms on each side. Therefore, the correct balanced equation is: 2Fe + 3Cl2 → 2FeCl3. Choice A (2Fe + 2Cl2 → 2FeCl3) is incorrect because it doesn't balance the Cl atoms properly. Choice C (3Fe + 2Cl2 → 3FeCl3) is incorrect because it doesn't balance the Fe atoms. Choice D (3Fe + 3Cl2 → 6FeCl3)

Correct Answer: A

Rationale: Answer A (NH₃) does not name a polar molecule because it has a trigonal pyramidal shape with a lone pair on nitrogen, causing an uneven distribution of electron density. This results in a net dipole moment, making NH₃ a polar molecule. In contrast, choices B (H₂S), C (SO₂), and D (CO₂) all have symmetrical shapes or polar bonds that cancel out the dipole moments, making them nonpolar molecules.