HESI A2
Chemistry HESI A2 Quizlet
1. Which of the following can act as a catalyst in a chemical reaction?
- A. Enzyme
- B. Light
- C. Water
- D. Metal
Correct answer: A
Rationale: Enzymes are biological catalysts that speed up chemical reactions without being consumed. They lower the activation energy required for the reaction to occur, facilitating and accelerating the process. Choice B, Light, is not a catalyst but can sometimes trigger reactions by providing energy. Choice C, Water, and choice D, Metal, are not catalysts but can participate in reactions as reactants.
2. What can stop the penetration of alpha particles?
- A. Aluminum foil
- B. Glass
- C. Piece of paper
- D. Plastic
Correct answer: C
Rationale: Alpha particles can be stopped by a piece of paper due to their low penetration power. The paper acts as a shield, effectively blocking the alpha particles from passing through. In contrast, materials like aluminum foil, glass, and plastic are not as effective as a simple piece of paper in stopping alpha particles. Aluminum foil is more effective against beta particles, gamma rays, and x-rays due to its higher density. Glass and plastic also provide some protection against beta particles and gamma rays, but they are less effective than a piece of paper against alpha particles.
3. What term is used to describe the emission of particles from an unstable nucleus?
- A. Radioactivity
- B. Radiation
- C. Decay
- D. Fusion
Correct answer: A
Rationale: Radioactivity is the term used to describe the emission of particles from an unstable nucleus. When a nucleus is unstable, it undergoes radioactive decay by emitting particles such as alpha or beta particles. This process releases energy and transforms the unstable nucleus into a more stable configuration. Choice B, 'Radiation,' is a broad term that encompasses various forms of energy emitted from a source; it is not specific to the emission from an unstable nucleus. Choice C, 'Decay,' is closely related but doesn't specifically indicate the emission of particles from an unstable nucleus. Choice D, 'Fusion,' refers to the process of combining nuclei to form a heavier nucleus, not the emission of particles from an unstable nucleus.
4. What number represents the number of protons an element has?
- A. Atomic mass
- B. Mass number
- C. Atomic number
- D. Neutron number
Correct answer: C
Rationale: The correct answer is C, atomic number. The atomic number corresponds to the number of protons in an element. This number is unique to each element and determines its placement on the periodic table. It is equal to the number of protons found in the nucleus of an atom of that element. Choice A, atomic mass, represents the average mass of an element's isotopes. Choice B, mass number, is the sum of protons and neutrons in an atom. Choice D, neutron number, specifically refers to the count of neutrons in an atom and not protons.
5. What effect does increasing the surface area of a reactant have?
- A. Decreases the reaction rate
- B. Has no effect
- C. Increases the reaction rate
- D. Stops the reaction
Correct answer: C
Rationale: Increasing the surface area of a reactant leads to more particles being exposed to the reaction, which in turn increases the reaction rate. This is because a larger surface area provides more sites for collisions between reacting particles, resulting in a higher frequency of successful collisions and thus accelerating the reaction. Choice A, 'Decreases the reaction rate,' is incorrect because increasing surface area actually accelerates the reaction. Choice B, 'Has no effect,' is incorrect as increasing surface area does have a significant effect on the reaction rate. Choice D, 'Stops the reaction,' is incorrect as increasing surface area does not stop the reaction but rather enhances it.
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