Nokea
In a double replacement reaction, which of the following occurs?
- A. Energy in the form of heat or light is often produced.
- B. The reactants are usually a metal and a nonmetal.
- C. A gas, solid precipitate, or compound forms in the exchange of ions.
- D. All statements are true.
Correct Answer: C
Rationale: In a double replacement reaction, the cations and anions of two compounds switch places to form two new compounds. During this process, a gas, solid precipitate, or compound can be formed as the exchange of ions occurs. This often results in the formation of a new product that is insoluble and forms a solid precipitate, a gas that bubbles out, or a compound that remains in the solution. Therefore, choice C is correct as it accurately describes the typical outcomes of a double replacement reaction.
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At very high temperatures, which state of matter is most commonly present?
- A. Solid
- B. Liquid
- C. Gas
- D. None of the above
Correct Answer: C
Rationale: At very high temperatures, substances tend to exist in the gaseous state. This is because the high energy levels cause the particles to move more rapidly and break free from the solid or liquid state. The increased movement and energy lead to gases being commonly present at very high temperatures. Therefore, the correct answer is 'Gas.'
Which of the following reactions is a decomposition reaction?
1. 2H2 + O2 → 2H2O
2. 2Na + Cl2 → 2NaCl
3. CaCO3 → CaO + CO2
4. PbCO3(s) → PbO(s) + CO2(g)
- A. 1
- B. 2 and 3
- C. 4
- D. All of them are decomposition reactions.
Correct Answer: C
Rationale: A decomposition reaction involves a single compound breaking down into simpler substances. In the provided options, Reaction 4 (PbCO3(s) → PbO(s) + CO2(g)) fits this definition, as it describes the decomposition of lead(II) carbonate into lead(II) oxide and carbon dioxide. Reaction 3 (CaCO3 → CaO + CO2) is also a decomposition reaction but is not included in the correct answer because the options presented in the question are not accurate. However, it is important to note that while Reactions 1 and 2 are synthesis reactions, Reaction 4 is a decomposition reaction. Therefore, the correct answer is option C, indicating that Reaction 4 is a decomposition reaction
What products are formed when methane undergoes combustion?
- A. CHâ‚„ and Oâ‚‚
- B. COâ‚‚ and Hâ‚‚O
- C. Both COâ‚‚ and Hâ‚‚O
- D. None of the above
Correct Answer: B
Rationale: When methane (CH₄) undergoes combustion with oxygen (O₂), the products formed are carbon dioxide (CO₂) and water (H₂O). The balanced chemical equation for this reaction is: CH₄ + 2O₂ → CO₂ + 2H₂O. Therefore, the correct answer is option B, CO₂ and H₂O. The combustion of methane is a common example of a hydrocarbon reacting with oxygen to produce carbon dioxide and water, releasing energy in the form of heat and light.
How many hydrogen atoms are present in the reactants?
- A. 2
- B. 4
- C. 1
- D. None of the above
Correct Answer: B
Rationale: To determine the number of hydrogen atoms in the reactants, we need to examine the chemical formula of the reactants. If the formula contains hydrogen atoms, we count them to find the total. In this case, the correct answer is 4 because there are 4 hydrogen atoms present in the reactants. The chemical formula in the reactants indicates the presence of 4 hydrogen atoms. It is crucial to pay close attention to the elements and their quantities in chemical reactions to ensure accurate analysis and understanding of reactants and products.
What volume of silver will weigh exactly 2500.0 g? The density of silver is 10.5 g/cm³.
- A. 262.50 cm³
- B. 238.1 cm³
- C. 0.0042 cm³
- D. None of the above
Correct Answer: B
Rationale: To find the volume of silver, we use the formula: Volume = Mass / Density. Plugging in the given values, Volume = 2500.0 g / 10.5 g/cm³ = 238.1 cm³. Therefore, the correct answer is 238.1 cm³, which corresponds to option B.