what is the role of a catalyst in a chemical reaction

HESI A2

Chemistry HESI A2 Quizlet

1. What is the role of a catalyst in a chemical reaction?

A. Slows down the reaction
B. Has no effect
C. Speeds up the reaction
D. Stops the reaction

Correct answer: C

Rationale: A catalyst speeds up a chemical reaction by lowering the activation energy required for the reaction to occur. It does not get consumed in the reaction and remains unchanged at the end, allowing it to facilitate multiple reaction cycles. Choice A is incorrect because a catalyst actually speeds up the reaction. Choice B is incorrect because catalysts do have an effect by accelerating the reaction. Choice D is incorrect because catalysts do not stop the reaction, but rather increase the reaction rate.

2. 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.

3. To the nearest whole number, what is the mass of one mole of water?

A. 16 g/mol
B. 18 g/mol
C. 20 g/mol
D. 22 g/mol

Correct answer: B

Rationale: The molar mass of water (H₂O) is calculated by adding the atomic masses of two hydrogen atoms (each with a molar mass of approximately 1 g/mol) and one oxygen atom (with a molar mass of approximately 16 g/mol). Therefore, the molar mass of water is approximately 18 g/mol, making choice B the correct answer. Choice A (16 g/mol) is incorrect because it represents the molar mass of oxygen, not water. Choices C (20 g/mol) and D (22 g/mol) are incorrect as they do not correspond to the molar mass of water.

4. What is the charge of an alpha particle?

A. -1
B. +1
C. +2
D. No charge

Correct answer: C

Rationale: An alpha particle consists of two protons and two neutrons, resulting in a total charge of +2 due to the presence of two positively charged protons. Therefore, the correct answer is C, indicating a charge of +2. Choices A, B, and D are incorrect because an alpha particle is positively charged due to the two protons it contains, resulting in a charge of +2.

5. On what concept is Kelvin based?

A. Freezing point
B. Absolute zero
C. Boiling point
D. Evaporation point

Correct answer: B

Rationale: The correct answer is B: Absolute zero. Kelvin is based on the concept of absolute zero, which is the point where molecular movement ceases entirely. This temperature scale starts at absolute zero (0K), where theoretically no molecular movement occurs. Choices A, C, and D are incorrect because Kelvin is not based on the freezing point, boiling point, or evaporation point, but rather on the absolute absence of molecular motion.