if gas a has four times the molar mass of gas b you would expect it to diffuse through a plug

HESI A2

Chemistry HESI A2 Practice Test

1. If gas A has four times the molar mass of gas B, you would expect it to diffuse through a plug ___________.

A. at half the rate of gas B
B. at twice the rate of gas B
C. at a quarter the rate of gas B
D. at four times the rate of gas B

Correct answer: A

Rationale: When comparing the diffusion rates of two gases, according to Graham's law of diffusion, the rate of diffusion is inversely proportional to the square root of the molar mass. If gas A has four times the molar mass of gas B, the square root of the molar masses ratio (4:1) is 2. This means that gas A would diffuse through a plug at half the rate of gas B. Therefore, the correct answer is A, at half the rate of gas B. Choices B, C, and D are incorrect because they do not reflect the correct relationship between the molar masses and the rates of diffusion according to Graham's law.

2. What is the name of the process by which a gas turns into a liquid?

A. Sublimation
B. Condensation
C. Evaporation
D. Deposition

Correct answer: B

Rationale: The correct answer is B: Condensation. Condensation is the process where gas transforms into a liquid. When gas cools down, it loses energy and its particles come closer, leading to the formation of liquid droplets. Sublimation is the direct transition from solid to gas without passing through the liquid state. Evaporation is the process of liquid turning into a gas, and deposition is the transition of gas directly into a solid. Therefore, choices A, C, and D are incorrect as they describe different phase transitions.

3. Which of the following elements is the most electronegative?

A. Oxygen
B. Fluorine
C. Nitrogen
D. Sodium

Correct answer: B

Rationale: Fluorine is the most electronegative element on the periodic table. It has the highest electronegativity value, indicating its strong ability to attract electrons in a chemical bond. This property makes it highly reactive, explaining why it is the correct answer in this question. Oxygen and Nitrogen are also electronegative elements, but they are not as electronegative as Fluorine. Sodium, on the other hand, is not electronegative; it is an electropositive element.

4. What defines a balanced chemical equation?

A. An equation where the number of atoms of each element is the same on both sides
B. An equation where there are more products than reactants
C. An equation where the number of molecules is balanced
D. An equation with equal masses on both sides

Correct answer: A

Rationale: A balanced chemical equation is one in which the number of atoms of each element is the same on both sides. This balance ensures the law of conservation of mass is upheld, where the total mass of the reactants equals the total mass of the products. Options B, C, and D are incorrect. Option B is incorrect as a balanced equation has an equal number of products and reactants. Option C is incorrect as balancing refers to the number of atoms, not molecules. Option D is incorrect as balancing is based on the number of atoms, not masses. Therefore, option A is the correct choice as it accurately describes a balanced chemical equation.

5. How many electron pairs are shared to form a triple covalent bond?

A. 1
B. 2
C. 3
D. 4

Correct answer: C

Rationale: The correct answer is C. In a triple covalent bond, three pairs of electrons are shared between two atoms. This sharing results in a total of six electrons being shared, making the bond strong. Choice A (1) is incorrect because a single covalent bond involves the sharing of one pair of electrons. Choice B (2) is incorrect as a double covalent bond consists of the sharing of two pairs of electrons. Choice D (4) is incorrect because there are only three pairs of electrons shared in a triple covalent bond, not four.