Nokea
One factor that affects rates of reaction is concentration. Which of these statements about concentration is/are correct?
- A. A higher concentration of reactants causes more effective collisions per unit time, leading to an increased reaction rate
- B. A lower concentration of reactants causes fewer effective collisions per unit time, leading to a decreased reaction rate
- C. A higher concentration of reactants causes more effective collisions per unit time, leading to a decreased reaction rate
- D. A higher concentration of reactants causes fewer effective collisions per unit time, leading to an increased reaction rate
Correct Answer: A
Rationale: A higher concentration of reactants causes more effective collisions per unit time, leading to an increased reaction rate. This is because a higher concentration means there are more reactant molecules in a given volume, increasing the likelihood of collisions between them. With more collisions occurring, there is a greater chance of successful collisions leading to the formation of products, hence increasing the reaction rate. Choice B is incorrect as a lower concentration decreases the number of collisions, reducing the reaction rate. Choice C is incorrect as a higher concentration increases collision frequency, which typically results in a higher reaction rate. Choice D is incorrect as a higher concentration usually leads to more collisions, thus increasing the reaction rate.
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What are mixtures of 2 or more metals called?
- A. Solutions
- B. Alloys
- C. Compounds
- D. Suspensions
Correct Answer: B
Rationale: Alloys are mixtures of two or more metals, combining their properties to create materials with enhanced characteristics. Examples of alloys include bronze (copper and tin) and steel (iron and carbon). Alloys are commonly used in various industries due to their improved strength, durability, and other desirable qualities. Solutions (Choice A) refer to a homogeneous mixture of two or more substances, where one substance is dissolved in another. Compounds (Choice C) are substances composed of two or more elements chemically combined in fixed proportions. Suspensions (Choice D) are heterogeneous mixtures where particles are dispersed but can settle out over time.
How many amino acids are essential for human life?
- A. 22
- B. 20
- C. 18
- D. 24
Correct Answer: B
Rationale: There are 20 essential amino acids required for human life. These amino acids cannot be synthesized by the body and must be obtained through the diet. They play crucial roles in various physiological functions and are necessary for protein synthesis and overall health. Choice A is incorrect because there are not 22 essential amino acids. Choice C is incorrect as there are more than 18 essential amino acids. Choice D is incorrect as there are not 24 essential amino acids for human life.
A molecule of water contains hydrogen and oxygen in a 1:8 ratio by mass. This is a statement of _____.
- A. The law of multiple proportions
- B. The law of conservation of mass
- C. The law of conservation of energy
- D. The law of constant composition
Correct Answer: D
Rationale: The statement that a molecule of water contains hydrogen and oxygen in a 1:8 ratio by mass is an example of the law of constant composition. This law states that all samples of a given chemical compound have the same elemental composition. In the case of water (H2O), no matter where you obtain a sample of water, it will always be composed of hydrogen and oxygen in a 1:8 ratio by mass. The law of multiple proportions deals with compounds that can be formed by the combination of elements in different ratios. The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction. The law of conservation of energy states that energy cannot be created or destroyed, only transferred or converted.
Which of the following is defined as the number of cycles of a wave that move past a fixed observation point per second?
- A. Wave
- B. Wavelength
- C. Frequency
- D. Wavefunction
Correct Answer: C
Rationale: Frequency is defined as the number of cycles of a wave that pass a fixed observation point per second. It is a fundamental characteristic of a wave and is measured in Hertz (Hz). The frequency of a wave determines its pitch in the case of sound waves and its color in the case of light waves.
Choice A, 'Wave,' is incorrect because a wave refers to the disturbance or oscillation that travels through a medium. Choice B, 'Wavelength,' is incorrect as it represents the distance between two corresponding points on a wave (e.g., crest to crest). Choice D, 'Wavefunction,' is not the correct answer as it is a mathematical function used in quantum mechanics to describe the behavior of particles and systems.
What are the s block and p block elements collectively known as?
- A. Transition elements
- B. Active elements
- C. Representative elements
- D. Inactive elements
Correct Answer: C
Rationale: The s block and p block elements are collectively known as representative elements. These elements are part of the main group elements in the periodic table, excluding the transition elements. The s block elements are located in groups 1 and 2, while the p block elements are found in groups 13 to 18. These elements display a diverse range of chemical behaviors and properties, representing the variety of elements in the periodic table. Choice A, Transition elements, is incorrect because transition elements are the elements in groups 3 to 12, which are located between the s block and the p block elements. Choice B, Active elements, is not a specific term used to refer to the s and p block elements collectively. Choice D, Inactive elements, is incorrect as the s and p block elements are known for their reactivity and participation in a wide range of chemical reactions.