Nokea
In combination reactions, what is always true?
- A. Involve only one reactant.
- B. Involve an element and a compound.
- C. Form only one product.
- D. Require oxygen gas.
Correct Answer: C
Rationale: In a combination reaction, two or more substances react to form a single product. This means that combination reactions always result in the formation of only one product from multiple reactants. It is a characteristic feature of these reactions that they lead to the creation of a single product. Therefore, the correct statement is that combination reactions form only one product.
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What is the SI unit of energy?
- A. ohm
- B. joule
- C. henry
- D. newton
Correct Answer: B
Rationale: The correct answer is B: joule. The joule is the SI unit of energy, defined as the work done by a force of one newton acting over a distance of one meter. It is extensively used to measure energy in various fields such as physics, chemistry, and engineering.
Which of the following substances is most dense?
- A. A block of gold weighing 12g and having a volume of 4.6cm³
- B. A cube weighing 6g and having a volume of 0.91cm³
- C. A block weighing 143g and having a volume of 24.3cm³
- D. None of the above.
Correct Answer: B
Rationale: The correct answer is 'B: A cube weighing 6g and having a volume of 0.91cm³.' Density is calculated as mass divided by volume. For each option: A) 12g/4.6cm³ ≈ 2.61 g/cm³, B) 6g/0.91cm³ ≈ 6.59 g/cm³, C) 143g/24.3cm³ ≈ 5.88 g/cm³. Therefore, option B is the most dense with a density of approximately 6.59 g/cm³.
What is the density of a piece of cork with a volume of 23.5 cm³ and a mass of 5.7g?
- A. 0.243g/cm³
- B. 4.123g/cm³
- C. 133.95g/cm³
- D. None of the above
Correct Answer: A
Rationale: Density is calculated by dividing the mass of an object by its volume. In this case, the density of the cork can be calculated by dividing 5.7g by 23.5 cm³, resulting in a density of approximately 0.243g/cm³. Therefore, choice A, 0.243g/cm³, is the correct answer as it accurately represents the density of the cork based on the provided values.
Identify the reactants in the chemical reaction below: CH₄ + 2O₂ → CO₂ + 2H₂O
- A. CHâ‚„ and Oâ‚‚
- B. COâ‚‚ and Hâ‚‚O
- C. Both
- D. None of the above
Correct Answer: A
Rationale: Reactants in a chemical reaction are the initial substances that are transformed into products. In this reaction, CHâ‚„ (methane) and Oâ‚‚ (oxygen) are the reactants, as they are the starting materials that undergo a chemical change to form COâ‚‚ (carbon dioxide) and 2Hâ‚‚O (water). The equation clearly shows that CHâ‚„ and Oâ‚‚ are on the left side of the reaction arrow, indicating that they are the reactants. Therefore, the correct answer is A: CHâ‚„ and Oâ‚‚.
What happens to an atom that has a positive charge?
- A. Gained an electron.
- B. Lost an electron.
- C. Gained a proton.
- D. Lost a proton.
Correct Answer: B
Rationale: When an atom has a positive charge, it means it has lost one or more electrons. Electrons carry a negative charge, so the loss of an electron results in the atom becoming positively charged. Therefore, the correct answer is B: Lost an electron.