what happens in a single displacement reaction

HESI A2

HESI A2 Chemistry Practice Questions

1. What happens in a single displacement reaction?

A. A compound decomposes into two substances.
B. An active element displaces a less active element.
C. A precipitate solid forms from the reaction of two solutions.
D. The oxidation states of atoms in the reactants change.

Correct answer: B

Rationale: In a single displacement reaction, an active element displaces a less active element in a compound. This process involves one element replacing another in a compound, resulting in the formation of a new compound. Option A is incorrect because a single displacement reaction does not involve the decomposition of a compound into two substances. Option C is incorrect because it describes a precipitation reaction, not a single displacement reaction. Option D is incorrect because it describes oxidation-reduction reactions, not specifically single displacement reactions.

2. What is the function of white blood cells?

A. To carry oxygen to the cells
B. To fight infection
C. To transport nutrients
D. To clot blood

Correct answer: B

Rationale: White blood cells are a vital part of the immune system. Their primary function is to fight infections by attacking bacteria, viruses, and other pathogens that enter the body. They play a crucial role in protecting the body against illnesses and maintaining overall health. Choice A is incorrect because the role of carrying oxygen to cells is primarily performed by red blood cells. Choice C is incorrect as the transportation of nutrients is mainly carried out by the bloodstream and specialized cells. Choice D is incorrect as the process of clotting blood is primarily mediated by platelets.

3. What is the main difference between a reversible and irreversible process in thermodynamics?

A. Reversible processes involve heat transfer, while irreversible processes do not.
B. Reversible processes occur instantaneously, while irreversible processes take time.
C. Reversible processes can be run in both directions with the same outcome, while irreversible processes cannot.
D. Reversible processes violate the first law of thermodynamics.

Correct answer: C

Rationale: A reversible process is an idealized process that can be reversed without leaving any change in either the system or the surroundings. In contrast, irreversible processes cannot be reversed and often involve entropy production or dissipation. Choice A is incorrect because both reversible and irreversible processes can involve heat transfer. Choice B is incorrect as the speed of a process does not determine its reversibility. Choice D is incorrect because reversible processes do not violate the first law of thermodynamics; they comply with it by maintaining a balance between energy inputs and outputs. Therefore, the correct answer is C, as it accurately captures the main difference between reversible and irreversible processes in thermodynamics.

4. What is the main function of the nervous system?

A. Transporting blood
B. Protecting the body from infection
C. Regulating body temperature
D. Digesting food

Correct answer: C

Rationale: The main function of the nervous system is to control and coordinate body activities by transmitting signals between different parts of the body and responding to internal and external stimuli. This allows for the regulation of body temperature, movement, sensory perception, and various other functions necessary for homeostasis. Choices A, B, and D are incorrect as they do not align with the primary role of the nervous system. Transporting blood is mainly carried out by the circulatory system, protecting the body from infection is a function of the immune system, and digesting food is the role of the digestive system.

5. The quality, safety, and efficacy of the new medicines are not known. What does efficacy mean?

A. Cost
B. Effectiveness
C. Quality
D. Usage

Correct answer: B

Rationale: Efficacy refers to how effective something is. In this context, it refers to the effectiveness of the new medicines. 'Cost' (Choice A) is incorrect as it relates to the price of something, not its effectiveness. 'Quality' (Choice C) is incorrect as it refers to the standard or degree of excellence. 'Usage' (Choice D) is incorrect as it refers to how something is used, not its effectiveness.