HESI A2
HESI A2 Chemistry Questions
1. How can water be boiled at room temperature?
- A. By lowering the pressure
- B. By increasing the pressure
- C. By decreasing the volume
- D. By raising the boiling point
Correct answer: A
Rationale: The boiling point of water is directly affected by pressure. By lowering the pressure, water can boil at a lower temperature, even at room temperature. This occurs because at lower pressures, the molecules of water have less resistance to escaping into the vapor phase, thus enabling boiling to occur at lower temperatures. Choices B, C, and D are incorrect because increasing the pressure, decreasing the volume, or raising the boiling point would actually require higher temperatures to boil water rather than achieving boiling at room temperature.
2. Which intermolecular force is the strongest?
- A. Dipole interactions
- B. Dispersion forces
- C. Hydrogen bonding
- D. Van der Waals forces
Correct answer: C
Rationale: Hydrogen bonding is the strongest intermolecular force due to its specific interaction between a hydrogen atom and a highly electronegative atom like nitrogen, oxygen, or fluorine. This type of bonding results in a very strong attraction between molecules, making it the strongest intermolecular force among the options provided. Dipole interactions (choice A) are weaker than hydrogen bonding as they occur between polar molecules. Dispersion forces (choice B) are the weakest intermolecular forces and are caused by temporary fluctuations in electron distribution. Van der Waals forces (choice D) are a broader term that encompasses dipole interactions and dispersion forces, making them weaker than hydrogen bonding.
3. In which state of matter are particles packed tightly together in a fixed position?
- A. Liquid
- B. Solid
- C. Gas
- D. Plasma
Correct answer: B
Rationale: In a 'solid' state, particles are tightly packed in fixed positions, maintaining a definite shape and volume. This arrangement allows solids to maintain a rigid structure. Liquids have particles that are close together but can move past each other, giving them the ability to flow and take the shape of their container. Gases have particles that are far apart and move freely, leading to their ability to expand to fill any container. Plasma is an ionized gas where particles have high energy levels and are not packed tightly together, making it an uncommon state of matter on Earth.
4. If electrons are not shared equally in a covalent bond, the bond is what?
- A. Polar
- B. Non-polar
- C. Ionic
- D. Hydrogen
Correct answer: A
Rationale: A polar covalent bond occurs when electrons are shared unequally between atoms. In this type of bond, one atom has a stronger pull on the shared electrons, leading to a partial positive and partial negative charge distribution within the molecule. Choice B, non-polar, is incorrect because in non-polar covalent bonds, electrons are shared equally between atoms. Choice C, ionic, is incorrect as ionic bonds involve a transfer of electrons rather than sharing. Choice D, hydrogen, is incorrect as it does not describe the nature of a covalent bond.
5. What is the charge of a gamma ray?
- A. -1
- B. +1
- C. +2
- D. No charge
Correct answer: D
Rationale: Gamma rays are a form of electromagnetic radiation with no charge. They are neutral particles that do not possess any electric charge. This characteristic allows them to be unaffected by electric or magnetic fields. Additionally, gamma rays travel at the speed of light in a vacuum. Choices A, B, and C are incorrect as gamma rays do not carry a charge of -1, +1, or +2; they are neutral entities.
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