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: A

Rationale: The correct answer is A: Covalent bonds. Covalent bonds involve a complete sharing of electrons between atoms with partially filled outer shells. This sharing allows atoms to achieve stable electron configurations. Hydrogen bonds involve an electrostatic attraction between a hydrogen atom and a highly electronegative atom. Proportional bonds are not a recognized type of chemical bond. Choice D, N/A, is not a valid option for this question.

Correct Answer: A

Rationale: The correct answer is A because at high pressure and high temperature, real gases have increased kinetic energy and are closer together, leading to decreased intermolecular forces. This results in gas molecules behaving more like ideal gases with negligible volume and no intermolecular interactions. Choice B is incorrect because at low pressure, real gases have low kinetic energy and are far apart, causing intermolecular forces to become more significant, deviating from ideal behavior. Choice C is incorrect as the boiling point of water is a specific condition related to water and does not necessarily indicate ideal gas behavior. Choice D is incorrect because under certain conditions of high pressure and high temperature, real gases can approach ideal behavior, demonstrating that real gases can exhibit ideal behavior under specific circumstances.

Correct Answer: D

Rationale: Rationale: 1. Wavelength is defined as the distance between adjacent peaks or troughs on a wave. 2. Frequency is the number of wave cycles per unit time, not the distance between peaks/troughs. 3. Wavenumber is the spatial frequency of a wave, not the distance between peaks/troughs. 4. Wave oscillation refers to the movement of particles in a wave, not the distance between peaks/troughs. Summary: The correct answer is D because wavelength specifically refers to the distance between adjacent peaks or troughs on a wave, whereas the other choices are related to different properties of waves.

Correct Answer: B

Rationale: The correct answer is B: Alpha radiation. Alpha radiation emits helium ions, which are essentially helium nuclei. These particles are large and have a low penetrating ability, so they can be stopped by a piece of paper. Beta radiation (choice A) consists of fast-moving electrons and can penetrate paper but can be stopped by aluminum. Gamma radiation (choice C) is high-energy electromagnetic radiation that requires thick lead or concrete to stop. X-ray radiation (choice D) is similar to gamma radiation and also requires dense materials for shielding. Therefore, alpha radiation is the only type that fits the description of emitting helium ions and being stopped by a piece of paper.