HESI A2
HESI A2 Chemistry Questions
1. What is the mass number of an atom with 6 protons, 6 neutrons, and 6 electrons?
- A. 12
- B. 18
- C. 6
- D. 8
Correct answer: A
Rationale: The mass number of an atom is the sum of protons and neutrons. In this case, the atom has 6 protons and 6 neutrons, thus the mass number is 6 + 6 = 12. Therefore, choice A (12) is the correct answer. Choices B (18), C (6), and D (8) are incorrect because the mass number is determined by the sum of protons and neutrons, not the number of electrons or a different combination of particles.
2. Which chemical reaction involves the breaking of a compound into its components?
- A. Decomposition reaction
- B. Combustion reaction
- C. Neutralization reaction
- D. Single displacement reaction
Correct answer: A
Rationale: The correct answer is A: Decomposition reaction. A decomposition reaction involves breaking down a compound into its components. During this reaction, a single compound breaks down into two or more simpler substances. This process is the opposite of a synthesis reaction where multiple substances combine to form a more complex compound. Choices B, C, and D are incorrect because combustion reaction involves burning a substance in oxygen, neutralization reaction involves the reaction between an acid and a base to form water and a salt, and single displacement reaction involves an element displacing another in a compound.
3. What is the name of the force that holds ionic compounds together?
- A. Covalent bonds
- B. Ionic bonds
- C. Hydrogen bonds
- D. Metallic bonds
Correct answer: B
Rationale: Ionic bonds are the forces that hold ionic compounds together. In ionic compounds, positively and negatively charged ions are held together by electrostatic forces of attraction, forming a stable structure. Covalent bonds involve the sharing of electrons between atoms, not the transfer of electrons like in ionic bonds. Hydrogen bonds are a type of intermolecular force, not the primary force in holding ionic compounds together. Metallic bonds are found in metals and involve a 'sea of electrons' that hold metal atoms together, different from the electrostatic attraction between ions in ionic compounds.
4. Which gas is released during photosynthesis?
- A. Carbon dioxide
- B. Oxygen
- C. Nitrogen
- D. Helium
Correct answer: B
Rationale: During photosynthesis, plants utilize carbon dioxide and water to produce glucose and oxygen. Oxygen is released as a byproduct of this process, which is essential for the survival of most living organisms that depend on it for respiration. Therefore, the correct answer is oxygen. Choices A, C, and D are incorrect. Carbon dioxide is utilized in photosynthesis, nitrogen is not directly involved in the process, and helium is not a gas released during photosynthesis.
5. What is the SI unit of energy?
- A. ohm
- B. joule
- C. henry
- D. newton
Correct answer: B
Rationale: The SI unit of energy is the 'joule'. The joule is defined as the work done when a force of one newton acts over a distance of one meter. It is the standard unit used to measure energy in the International System of Units (SI). Therefore, the correct answer is 'joule.' Choice A, 'ohm,' is the SI unit of electrical resistance, not energy. Choice C, 'henry,' is the SI unit of inductance, not energy. Choice D, 'newton,' is the SI unit of force, not energy. Hence, they are all incorrect in the context of measuring energy.
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