which of these factors would not affect rates of reaction

HESI A2

Chemistry HESI A2 Practice Test

1. Which of the following factors would not affect rates of reaction?

A. Temperature
B. Surface area
C. Pressure
D. Time

Correct answer: D

Rationale: Time would not directly affect rates of reaction. The rate of a chemical reaction is determined by factors that affect the frequency of successful collisions between reactant molecules, leading to a reaction. Temperature, surface area, and pressure can influence reaction rates by impacting the kinetic energy of molecules, the exposed surface for collisions, and the concentration of reactants, respectively. However, time, in the context of this question, does not alter the rate of reaction but may affect the extent of the reaction or the amount of product formed over time.

2. Which of these represents a strong acid?

A. CH₃COOH
B. H₂SO₄
C. NH₃
D. KOH

Correct answer: B

Rationale: Among the options provided, H₂SO₄ (sulfuric acid) represents a strong acid. Strong acids completely ionize in water to produce a high concentration of H+ ions. Sulfuric acid is a strong acid known for its ability to dissociate almost completely in water, making it a strong acid. Choice A, CH₃COOH (acetic acid), is a weak acid that only partially dissociates in water. Choices C and D, NH₃ (ammonia) and KOH (potassium hydroxide), are bases and not acids.

3. How can the reaction rate of a chemical reaction be increased?

A. Increase the temperature
B. Increase the surface area
C. Increase the concentration of reactants
D. Add a catalyst

Correct answer: A

Rationale: To increase the reaction rate of a chemical reaction, one effective method is to increase the temperature. Raising the temperature provides more energy to the reacting particles, enabling them to collide more frequently and with higher energy, leading to an increase in the reaction rate. While increasing the surface area, concentration of reactants, and adding a catalyst are strategies that can also enhance the reaction rate, raising the temperature has the most direct and immediate impact. Increasing the surface area allows for more contact between reactants, increasing the concentration provides more reactant particles to collide, and adding a catalyst lowers the activation energy required for the reaction to occur. However, these methods may not have as immediate and significant an effect as increasing the temperature.

4. What charge do Group VA elements typically have?

A. -1
B. -2
C. -3
D. 0

Correct answer: C

Rationale: Group VA elements, also known as Group 15 elements, typically have a charge of -3. This is because they have five valence electrons and tend to gain three electrons to achieve a stable octet configuration, resulting in a -3 charge. Choice A (-1) and Choice B (-2) are incorrect because Group VA elements need to gain three electrons to reach a stable electron configuration, not just one or two. Choice D (0) is also incorrect because Group VA elements do not lose electrons to form a charge of 0.

5. Which of these elements has the greatest atomic mass?

A. Au
B. Ba
C. I
D. W

Correct answer: D

Rationale: Among the elements listed, Tungsten (W) has the greatest atomic mass. The atomic mass of Tungsten is approximately 183.84 atomic mass units (amu), while the atomic masses of the other elements listed are as follows: Gold (Au) is around 196.97 amu, Barium (Ba) is approximately 137.33 amu, and Iodine (I) is about 126.90 amu. Therefore, Tungsten (W) has the greatest atomic mass out of the given elements. Gold (Au) has a higher atomic mass than Barium (Ba) and Iodine (I), making choices A, B, and C incorrect.