Chemistry HESI A2 Practice Test

Correct Answer: A

Rationale: The correct answer is A: 92. Uranium-235 has an atomic number of 92, which represents the number of protons in its nucleus. Neutrons are calculated by subtracting the atomic number from the mass number (235 - 92 = 143), so there are 143 neutrons in uranium-235. This makes option A the correct choice. Options B, C, and D are incorrect because they do not accurately reflect the number of neutrons in uranium-235 based on its atomic number and mass number.

Correct Answer: C

Rationale: The given chemical equation shows aluminum replacing hydrogen in sulfuric acid, which is a single replacement reaction. In this type of reaction, one element displaces another in a compound. Here, Al replaces H in H2SO4 to form Al2(SO4)3 and HNO3. The other choices are incorrect because a decomposition reaction involves a single compound breaking down into simpler substances, a synthesis reaction involves two or more substances combining to form a new compound, and a double replacement reaction involves the exchange of ions between two compounds.

Correct Answer: B

Rationale: The correct answer is B: Absolute zero. Kelvin is based on the concept of absolute zero, which is the coldest possible temperature where particles have minimal kinetic energy. This forms the foundation for the Kelvin temperature scale. A: Freezing point is incorrect because Kelvin is not specifically based on the freezing point of any substance. C: Boiling point is incorrect as Kelvin is not directly linked to the boiling point of any substance. D: Evaporation point is incorrect because Kelvin does not relate to the point at which a substance undergoes evaporation.

Correct Answer: D

Rationale: The correct answer is D: Time. Time does not directly impact rates of reaction; rather, it is the duration over which a reaction occurs. Temperature affects reaction rates by increasing kinetic energy, surface area by exposing more reactant molecules, and pressure by affecting collision frequency. Time is not an influencing factor in itself, but the overall reaction rate may depend on the time taken for the reaction to complete.

Correct Answer: A

Rationale: The correct answer is A: 0 moles. In the given scenario, the volume of the solution is 0 L, which means there is no solution to contain any amount of salt. Molarity is the concentration of a solution in moles of solute per liter of solution. Since the volume is 0 L, there are no moles of salt present. Choice B, C, and D are incorrect because they suggest there are moles of salt present, which is not possible when the volume of the solution is 0 L.