HESI A2 Chemistry Questions

Correct Answer: A

Rationale: The correct answer is A: Synthesis reaction. In a synthesis reaction, two or more reactants combine to form a single product. This type of reaction is characterized by the formation of a more complex molecule from simpler ones. The other choices are incorrect because: B: Combustion reaction involves the rapid combination of a substance with oxygen, producing heat and light. C: Decomposition reaction involves the breakdown of a compound into simpler substances. D: Double displacement reaction involves the exchange of ions between two compounds to form two new compounds.

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: To speed up reactions. Enzymes work by lowering the activation energy required for a reaction to occur, thereby speeding up the reaction without being consumed in the process. This allows reactions to occur at a faster rate than they would without the enzyme. Enzymes do not provide energy (choice A) but rather facilitate energy transfer during reactions. While enzymes decrease activation energy (choice C), this is a means to speed up reactions rather than their primary function. Enzymes act as catalysts (choice D) by increasing the rate of reactions, making them an essential component in biochemical processes.

Correct Answer: C

Rationale: The correct answer is C: Argon. Noble gases are elements in Group 18 of the periodic table with full valence electron shells, making them stable and non-reactive. Argon is a noble gas with 8 valence electrons, fulfilling the octet rule. Hydrogen (A) is a nonmetal in Group 1, Fluorine (B) is a halogen in Group 17, and Nitrogen (D) is a nonmetal in Group 15, none of which are noble gases.

Correct Answer: A

Rationale: The correct answer is A: Freezing point depression. Colligative properties depend on the number of solute particles in a solution, not the nature of the solute. Freezing point depression occurs because the presence of solute particles disrupts the formation of orderly ice crystals, lowering the freezing point of the solution. Viscosity and surface tension are not colligative properties as they are not solely dependent on the number of solute particles. Boiling point elevation is a colligative property, but the question specifically asks for a property related to freezing, making it incorrect in this context.