Q11. What type of reaction is represented by the following equation: AB → A + B?
a) Synthesis reaction
b) Decomposition reaction
c) Single displacement reaction
d) Double displacement reaction
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Correct Answer: b) Decomposition reaction
Explanation: A decomposition reaction involves the breakdown of a single compound into two or more simpler substances. In the given equation, the compound AB decomposes into its constituent elements, A and B.
Q12. Which of the following statements about endothermic reactions is true?
a) They release heat to the surroundings
b) They absorb heat from the surroundings
c) They proceed spontaneously
d) They always involve the formation of gases
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Correct Answer: b) They absorb heat from the surroundings
Explanation: Endothermic reactions absorb heat from the surroundings, causing a decrease in temperature. These reactions typically require an input of energy to proceed and are characterized by a positive enthalpy change.
Q13. Which of the following is NOT a sign that a chemical reaction has occurred?
a) Formation of a precipitate
b) Color change
c) Release of odor
d) No change in temperature
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Correct Answer: d) No change in temperature
Explanation: A change in temperature is often observed in chemical reactions, whether it be an increase (exothermic reaction) or a decrease (endothermic reaction). Therefore, no change in temperature is not a sign that a chemical reaction has occurred.
Q14. In which type of reaction does a single compound break down into two or more simpler substances?
a) Synthesis reaction
b) Decomposition reaction
c) Single displacement reaction
d) Double displacement reaction
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Correct Answer: b) Decomposition reaction
Explanation: A decomposition reaction involves the breakdown of a single compound into two or more simpler substances. This can occur through various mechanisms, such as thermal decomposition, electrolysis, or photolysis.
Q15. What type of reaction occurs when a more reactive element displaces a less reactive element from its compound?
a) Synthesis reaction
b) Decomposition reaction
c) Single displacement reaction
d) Double displacement reaction
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Correct Answer: c) Single displacement reaction
Explanation: In a single displacement reaction, also known as a substitution reaction, a more reactive element displaces a less reactive element from its compound. This occurs when an element in a compound is replaced by another element that is higher in the activity series.
Q16. What is the term for a reaction that releases energy in the form of light or heat?
a) Exothermic reaction
b) Endothermic reaction
c) Spontaneous reaction
d) Redox reaction
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Correct Answer: a) Exothermic reaction
Explanation: Exothermic reactions release energy in the form of heat or light to the surroundings. This energy release often results in an increase in temperature in the surrounding environment.
Q17. Which of the following statements about combustion reactions is true?
a) They always produce carbon dioxide and water
b) They are typically endothermic
c) They involve the reaction of a substance with oxygen
d) They do not release energy
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Correct Answer: c) They involve the reaction of a substance with oxygen
Explanation: Combustion reactions involve the rapid reaction of a substance with oxygen, often resulting in the release of heat and light. While combustion of hydrocarbons typically produces carbon dioxide and water, not all combustion reactions follow this pattern.
Q18. Which of the following is an example of a spontaneous reaction?
a) Photosynthesis
b) Rusting of iron
c) Decomposition of hydrogen peroxide
d) Electrolysis of water
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Correct Answer: b) Rusting of iron
Explanation: Spontaneous reactions occur naturally without external intervention. The rusting of iron, for example, occurs spontaneously in the presence of oxygen and moisture, leading to the formation of iron oxide (rust) over time.
Q19. Which of the following is NOT a type of chemical reaction?
a) Oxidation reaction
b) Neutralization reaction
c) Electrolysis reaction
d) Mechanical reaction
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Correct Answer: d) Mechanical reaction
Explanation: Mechanical reactions do not involve changes in chemical composition and are typically physical processes, such as grinding, crushing, or bending, which alter the physical properties of substances without forming new chemical bonds.
Q20. What type of reaction occurs when two reactants exchange ions to form two new compounds?
a) Synthesis reaction
b) Decomposition reaction
c) Single displacement reaction
d) Double displacement reaction
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Correct Answer: d) Double displacement reaction
Explanation: In a double displacement reaction, also known as a metathesis reaction, two reactants exchange ions to form two new compounds. This exchange typically occurs in aqueous solutions, leading to the formation of a precipitate, gas, or water.