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: A

Rationale: The correct answer is A: Arrangement of atoms. Allotropes are different forms of the same element with different structures of atoms. This distinction is based on the specific arrangement of atoms in each allotrope, leading to varying physical and chemical properties. Gram atomic mass (B) is related to the weight of an atom, not the arrangement. Physical state (C) refers to the form of matter (solid, liquid, gas), not the atomic structure. Stability (D) may be a factor influenced by the arrangement of atoms, but it is not the primary distinguishing feature among allotropes.

Correct Answer: D

Rationale: The correct answer is D: Lye. Lye, also known as sodium hydroxide, forms hydroxide ions (OH-) when placed in water due to its highly alkaline nature. When lye dissociates in water, it releases hydroxide ions, which contribute to the solution's basicity. Lemon juice (A) and vinegar (C) are acidic solutions that release hydrogen ions (H+) in water. Battery acid (B) typically contains sulfuric acid, which also releases hydrogen ions in water. Therefore, only lye is the substance that forms hydroxide ions when placed in water, making it the correct answer.

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: The correct answer is A: 2. Helium-4 has an atomic number of 2, which represents the number of protons in its nucleus. Since the atomic number is the sum of protons and neutrons, and helium-4 has 2 protons, it must also have 2 neutrons to make the total atomic mass 4. Therefore, there are 2 neutrons in an atom of helium-4. Choice B: 3 is incorrect because it does not match the atomic number of helium-4. Choice C: 4 is incorrect as it is the total atomic mass of helium-4, not the number of neutrons. Choice D: 6 is incorrect as it does not correspond to the atomic structure of helium-4.