which element would you expect to be least reactive

HESI A2

Chemistry HESI A2 Practice Test

1. Which element would you expect to be least reactive?

A. Li
B. Cr
C. Nd
D. Xe

Correct answer: D

Rationale: Xenon (Xe) is a noble gas located in Group 18 of the periodic table. Noble gases are known for their stable and unreactive nature due to having a full outer shell of electrons. Therefore, xenon would be expected to be the least reactive among the given elements. Choice A (Li) is a metal in Group 1 of the periodic table, which tends to be reactive, especially with water. Choice B (Cr) is a transition metal known for its reactivity in some forms. Choice C (Nd) is a rare earth element, which can exhibit varying reactivity depending on the compound or environment.

2. Which of the following is a colligative property of a solution?

A. Freezing point depression
B. Viscosity
C. Surface tension
D. Boiling point elevation

Correct answer: A

Rationale: A colligative property is a property that depends on the number of solute particles in a solution, not on the identity of the solute particles. Freezing point depression is one such property, where adding a solute to a solvent lowers the freezing point of the solution compared to the pure solvent. This phenomenon occurs because the presence of solute particles disrupts the formation of the regular crystal lattice structure, requiring a lower temperature for solidification to occur. Choices B, C, and D are not colligative properties. Viscosity and surface tension are not dependent on the number of solute particles but on intermolecular forces and molecular interactions. Boiling point elevation is another colligative property, but in this case, the question asked for a colligative property of a solution, making freezing point depression the correct answer.

3. What is 0 K equal to in °C?

A. -300°C
B. -273°C
C. -250°C
D. -200°C

Correct answer: B

Rationale: 0 Kelvin, also known as absolute zero, is equal to -273°C. This is the point at which all molecular motion stops, making it the lowest possible temperature on the Kelvin scale. Choice A (-300°C) is incorrect as it is not the correct conversion of 0 K to °C. Choice C (-250°C) and Choice D (-200°C) are also incorrect as they do not correspond to the accurate conversion of 0 K to °C.

4. What type of chemical reaction involves the combination of two elements to form a product?

A. Decomposition
B. Combustion
C. Synthesis
D. Double replacement

Correct answer: C

Rationale: A synthesis reaction involves the combination of two or more substances to form a single, more complex product. In the context of chemical reactions, it specifically refers to the combination of two elements to form a compound. Therefore, the correct answer is C. Decomposition reactions involve the breakdown of a single compound into simpler substances (opposite of synthesis). Combustion reactions involve a substance reacting with oxygen to produce heat and light, not the combination of elements. Double replacement reactions involve the exchange of ions between two compounds, leading to the formation of two new compounds, not the combination of two elements.

5. What are the three types of intermolecular forces?

A. Ionic, covalent, hydrogen
B. Hydrogen bonding, dipole interactions, dispersion forces
C. Van der Waals, ionic, covalent
D. Hydrogen, Van der Waals, dispersion forces

Correct answer: B

Rationale: The three types of intermolecular forces are hydrogen bonding, dipole interactions, and dispersion forces. Option A includes ionic and covalent bonds, which are intramolecular forces, not intermolecular. Option C includes van der Waals forces, which encompass dipole interactions and dispersion forces, but also includes ionic and covalent bonds. Option D is close but misses dipole interactions, which are distinct from hydrogen bonding and dispersion forces. Therefore, option B is the correct choice as it includes the three specific types of intermolecular forces.