HESI A2 Chemistry Questions

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: 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.

Correct Answer: C

Rationale: The correct answer is C: Evaporation. During evaporation, a liquid changes into a gas at the surface level due to the absorption of heat energy. This process occurs at temperatures below the boiling point of the liquid. Condensation (Choice A) is the opposite process, where a gas turns into a liquid. Sublimation (Choice B) is the phase change from solid directly to gas without passing through the liquid phase. Melting (Choice D) is the phase change from solid to liquid. Therefore, the correct choice for the phase change from liquid to gas is evaporation.

Correct Answer: A

Rationale: The correct answer is A: Decomposition reaction. In a decomposition reaction, a compound is broken down into its individual components. This process involves the breaking of chemical bonds within the compound, resulting in the formation of simpler substances. This type of reaction is characterized by one reactant and multiple products. In contrast, the other choices - B: Combustion reaction, C: Neutralization reaction, and D: Single displacement reaction - do not involve the breaking down of a compound into its components but rather involve different types of chemical transformations. Combustion reaction involves the reaction of a substance with oxygen to produce heat and light, neutralization reaction involves the reaction between an acid and a base to form water and a salt, and single displacement reaction involves the replacement of one element in a compound by another element.

Correct Answer: C

Rationale: The correct answer is C: Electrons. Electrons are negatively charged subatomic particles found in the electron cloud surrounding the nucleus of an atom. They are responsible for chemical bonding and electricity conduction. Protons (A) are positively charged, neutrons (B) are neutral, and isotopes (D) are atoms with the same number of protons but different number of neutrons.