HESI A2 Chemistry Questions

Correct Answer: A

Rationale: The correct answer is A: boron. Diatomic molecules consist of two atoms of the same element bonded together. Boron exists as a monatomic element, meaning it exists as single atoms. Fluorine, oxygen, and nitrogen exist naturally as diatomic molecules (F2, O2, N2) due to their stability when bonded together. Boron does not form diatomic molecules because it is less stable in that form.

Correct Answer: B

Rationale: The correct answer is B: Solid. In solids, particles are tightly packed in a fixed position due to strong intermolecular forces holding them in place. This results in a definite shape and volume. In liquids (choice A), particles are close together but not in fixed positions, allowing them to flow and take the shape of their container. In gases (choice C), particles are far apart and move freely, leading to indefinite shape and volume. In plasma (choice D), particles are highly energized, ionized, and not bound together, making them not tightly packed or in fixed positions.

Correct Answer: B

Rationale: The correct answer is B: It releases heat. In an exothermic reaction, energy is released in the form of heat to the surroundings. This results in a temperature increase in the surrounding environment. The other choices are incorrect because: A: It absorbs heat - This is a characteristic of an endothermic reaction, where heat is absorbed from the surroundings. C: It remains neutral - This does not describe the nature of an exothermic reaction, which involves the release of heat. D: It requires energy input - This is more in line with an endothermic reaction, where energy input is needed to drive the reaction.

Correct Answer: A

Rationale: The correct answer is A: Carbon dioxide. When an acid reacts with a carbonate, it produces carbon dioxide gas due to the chemical reaction. The acid donates hydrogen ions to the carbonate, forming carbonic acid, which then breaks down into water and carbon dioxide. Oxygen (B), hydrogen (C), and nitrogen (D) are not produced during this specific reaction and are not part of the chemical equation for the reaction between an acid and a carbonate.

Correct Answer: B

Rationale: The correct answer is B: Halogens. Halogens are a group of elements in Group 17 of the periodic table, including chlorine, fluorine, and iodine. They are known for their high reactivity and tendency to form salts with metals. Alkali metals (A) are in Group 1, transition metals (C) are in the middle part of the periodic table, and noble gases (D) are in Group 18. These choices are incorrect as they do not include chlorine, fluorine, and iodine, which are characteristic of the halogens.