HESI A2 Chemistry Questions

Correct Answer: B

Rationale: The correct answer is B: Production of gas. In a chemical change, new substances are formed with different properties. The production of gas is a sign of a chemical reaction due to the formation of new molecules. Choices A, C, and D are physical changes, not chemical changes. A change in shape (A) is a physical change as it does not alter the chemical composition. Melting (C) and freezing (D) are also physical changes, involving the state of matter without changing the chemical composition.

Correct Answer: B

Rationale: The correct answer is B: Neon. Noble gases are a group of elements that are inert and have a full outer electron shell, making them stable and unreactive. Neon belongs to the noble gas group in the periodic table, with a full outer electron shell, making it stable. Oxygen (A) is a reactive nonmetal, hydrogen (C) is a nonmetal but not a noble gas, and argon (D) is also a noble gas but not the correct answer in this case.

Correct Answer: B

Rationale: The correct answer is B: To speed up reactions. Enzymes work by lowering the activation energy required for a reaction to occur, thereby speeding up the reaction without being consumed in the process. This allows reactions to occur at a faster rate than they would without the enzyme. Enzymes do not provide energy (choice A) but rather facilitate energy transfer during reactions. While enzymes decrease activation energy (choice C), this is a means to speed up reactions rather than their primary function. Enzymes act as catalysts (choice D) by increasing the rate of reactions, making them an essential component in biochemical processes.

Correct Answer: A

Rationale: The correct answer is A: Uranium. Uranium has the highest atomic number among the options provided. Atomic number represents the number of protons in the nucleus of an atom. Uranium has an atomic number of 92, which is higher than the other elements listed. Hydrogen has an atomic number of 1, Radon has an atomic number of 86, and Bismuth has an atomic number of 83. Therefore, Uranium has the highest atomic number, making it the correct choice.

Correct Answer: A

Rationale: The correct answer is A: Fluorine. Fluorine has the highest electronegativity because it has the smallest atomic size among the choices, leading to a stronger attraction for electrons. This makes it more likely to attract electrons in a chemical bond. Chlorine, Nitrogen, and Oxygen have lower electronegativities compared to Fluorine due to their larger atomic sizes, resulting in weaker electron-attracting capabilities. Remember, electronegativity generally increases across a period from left to right in the periodic table.