HESI A2 Chemistry Practice Test

Correct Answer: A

Rationale: The correct answer is A: A higher concentration of reactants causes more effective collisions per unit time, leading to an increased reaction rate. This is because a higher concentration means there are more reactant molecules in a given volume, increasing the chances of collisions between them. With more collisions occurring, the likelihood of effective collisions (those with sufficient energy and correct orientation) also increases, resulting in a faster reaction rate. Choices B, C, and D are incorrect: B: A lower concentration of reactants causes fewer effective collisions per unit time, leading to a decreased reaction rate - This is incorrect as lower concentration reduces the number of collisions, including effective collisions, hence decreasing the reaction rate. C: A higher concentration of reactants causes more effective collisions per unit time, leading to a decreased reaction rate - This is contradictory and illogical as a higher concentration increasing effective collisions would logically lead to an increased reaction rate. D: A higher concentration of reactants causes fewer effective collisions per unit time, leading

Correct Answer: D

Rationale: Rationale: 1. Statement A is correct as solubility is indeed defined by the concentration in a saturated solution. 2. Statement B is correct as substances with very low solubilities are typically considered insoluble. 3. Statement C is correct as a saturated solution cannot dissolve any more solute. 4. Therefore, all statements (A, B, and C) are correct, making option D the correct choice. Other options are incorrect as they do not accurately define solubility or saturated solutions.

Correct Answer: C

Rationale: Henry's Law states that the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid (P = kC). This means that as the partial pressure of the gas increases, the amount of gas that dissolves in the liquid also increases. This relationship is specifically for gases and volatile substances in liquids. Boyle's Law relates pressure and volume, Gay-Lussac's Law relates pressure and temperature, and Charles' Law relates volume and temperature. Therefore, the correct answer is C, Henry's Law, because it directly describes the relationship between gas solubility and partial pressure.

Correct Answer: A

Rationale: The correct answer is A: Protons. Isotopes of an element have the same number of protons, as the number of protons determines the element's identity. Isotopes differ in the number of neutrons, leading to variations in atomic mass. Neutrons play a role in the stability and mass of an isotope but do not affect the element's identity. Protons and electrons determine the overall charge of an atom, but isotopes only vary in the number of neutrons, not electrons. Thus, the correct answer is A as it aligns with the fundamental concept of isotopes having the same number of protons.

Correct Answer: A

Rationale: The correct answer is A: Brownian motion. This phenomenon was first observed by Robert Brown in 1827. Brownian motion is the random movement of small particles suspended in a liquid, caused by the unbalanced impacts of molecules on the particle. This motion is a result of the constant and random motion of molecules in the liquid colliding with the particle, causing it to move in a zigzag pattern. Grey's kinesis (choice B) and Boyle's wave (choice C) are not valid terms associated with this concept and are therefore incorrect. Choice D (None of the above) is also incorrect as Brownian motion accurately describes the phenomenon described in the question.