HESI A2
HESI A2 Chemistry Practice Test
1. Which of the following is defined as the number of cycles of a wave that move past a fixed observation point per second?
- A. Wave
- B. Wavelength
- C. Frequency
- D. Wavefunction
Correct answer: C
Rationale: Frequency is defined as the number of cycles of a wave that pass a fixed observation point per second. It is a fundamental characteristic of a wave and is measured in Hertz (Hz). The frequency of a wave determines its pitch in the case of sound waves and its color in the case of light waves. Choice A, 'Wave,' is incorrect because a wave refers to the disturbance or oscillation that travels through a medium. Choice B, 'Wavelength,' is incorrect as it represents the distance between two corresponding points on a wave (e.g., crest to crest). Choice D, 'Wavefunction,' is not the correct answer as it is a mathematical function used in quantum mechanics to describe the behavior of particles and systems.
2. What is defined as the distance between adjacent peaks or adjacent troughs on a wave?
- A. Frequency
- B. Wavenumber
- C. Wave oscillation
- D. Wavelength
Correct answer: D
Rationale: Wavelength is correctly defined as the distance between adjacent peaks or adjacent troughs on a wave. It is a crucial characteristic of waves, influencing properties such as color in light waves and pitch in sound waves. By altering the wavelength, significant changes in the wave's perception and attributes can be observed. Choice A, Frequency, refers to the number of occurrences of a repeating event per unit of time and is not related to the distance between peaks or troughs. Choice B, Wavenumber, represents the spatial frequency of a wave in terms of cycles per unit distance, not the distance between adjacent peaks. Choice C, Wave oscillation, does not specifically define the distance between adjacent peaks or troughs but rather the movement of a wave back and forth.
3. Which of the following lists four factors that affect rates of reaction?
- A. Barometric pressure, particle size, concentration, and the presence of a facilitator
- B. Temperature, particle size, concentration, and the presence of a catalyst
- C. Temperature, container material, elevation, and the presence of instability
- D. Volatility, particle size, concentration, and the presence of a catalyst
Correct answer: B
Rationale: The correct answer is B. The factors that influence rates of reaction are temperature, particle size, concentration, and the presence of a catalyst. Temperature affects the speed of molecules, particle size impacts the available surface area for reactions, concentration influences the collision frequency between reactant molecules, and catalysts accelerate reactions by providing an alternative pathway with lower activation energy. Choices A, C, and D are incorrect as they either include irrelevant factors that do not affect reaction rates (barometric pressure, container material, elevation, and volatility) or lack important factors that do influence reaction rates (like a catalyst).
4. The volume of a gas is directly proportional to its absolute temperature at constant pressure. This is a statement of:
- A. Combined Gas Law
- B. Boyle's Law
- C. Charles' Law
- D. The Ideal Gas Law
Correct answer: C
Rationale: Charles' Law states that the volume of a gas is directly proportional to its absolute temperature at constant pressure. This means that as the temperature of a gas increases, its volume also increases proportionally, and vice versa. This relationship between temperature and volume is a key feature of Charles' Law. The Combined Gas Law involves the relationships between pressure, volume, and temperature of a gas. Boyle's Law describes the inverse relationship between the pressure and volume of a gas at constant temperature. The Ideal Gas Law combines Boyle's Law, Charles' Law, and Avogadro's Law into a single expression. Therefore, the correct answer is Charles' Law, as it specifically describes the direct relationship between the temperature and volume of a gas.
5. Which law states that the pressure of an ideal gas is inversely proportional to its volume, given that the temperature and amount of gas remain constant?
- A. Henry's law
- B. Dalton's law
- C. Brown's law
- D. Boyle's law
Correct answer: D
Rationale: Boyle's law describes the relationship between the pressure and volume of an ideal gas when the temperature and amount of gas are constant. According to Boyle's law, if the pressure of a gas increases, its volume decreases proportionally, and vice versa. This law is expressed by the equation P1V1 = P2V2, where P1 and V1 represent the initial pressure and volume, while P2 and V2 represent the final pressure and volume when the temperature and amount of gas remain unchanged. Understanding Boyle's law is essential in comprehending the behavior of gases under varying conditions and is fundamental in the study of thermodynamics. The other choices are incorrect: - Henry's law deals with the solubility of gases in liquids, not the relationship between pressure and volume of gases. - Dalton's law states that the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of individual gases, not the pressure-volume relationship. - Brown's law is a fabricated concept and does not exist in the context of gas laws.
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