Chemistry Test Chemical Reactions 3 — Questions and Answers
Question 1: What does it mean for a chemical reaction to be exothermic?
- It absorbs heat from the surroundings
- It releases heat into the surroundings (Correct answer)
- It requires ultraviolet light to proceed
- It produces only gaseous products
Correct answer: It releases heat into the surroundings
Exothermic reactions release energy as heat, making the surroundings feel warmer.
Question 2: In a neutralization reaction, an acid reacts with a base to produce:
- An oxide and hydrogen gas
- A salt and water (Correct answer)
- A precipitate and carbon dioxide
- An ester and oxygen
Correct answer: A salt and water
Neutralization reactions produce a salt and water when an acid and base combine.
Question 3: Which factor does NOT affect the rate of a chemical reaction?
- Concentration of reactants
- Surface area of solid reactants
- Color of the reaction vessel (Correct answer)
- Presence of a catalyst
Correct answer: Color of the reaction vessel
The color of the reaction vessel has no effect on reaction rate; concentration, surface area, and catalysts all influence how fast reactions proceed.
Question 4: What is a precipitate in a double displacement reaction?
- A gas released during the reaction
- An insoluble solid that forms in solution (Correct answer)
- The solvent left after evaporation
- A catalyst added to speed up the reaction
Correct answer: An insoluble solid that forms in solution
A precipitate is an insoluble solid product that forms when two solutions are mixed in a double displacement reaction.
Question 5: In the combustion reaction CH₄ + 2O₂ → CO₂ + 2H₂O, what is oxidized?
- Oxygen
- Carbon dioxide
- Carbon in methane (Correct answer)
- Water
Correct answer: Carbon in methane
Carbon in methane is oxidized because it loses electrons (its oxidation state increases from -4 to +4).
Question 6: Which statement about reaction equilibrium is correct?
- The reaction has completely stopped
- Concentrations of all species are equal
- Forward and reverse reaction rates are equal (Correct answer)
- Only the reverse reaction continues
Correct answer: Forward and reverse reaction rates are equal
At equilibrium, the forward and reverse reactions occur at the same rate, so concentrations remain constant but are not necessarily equal.
Question 7: What type of reaction is: 2KClO₃ → 2KCl + 3O₂?
- Synthesis
- Decomposition (Correct answer)
- Single displacement
- Combustion
Correct answer: Decomposition
This is a decomposition reaction because one compound (KClO₃) breaks down into two simpler substances.
Chemistry Test Chemical Reactions 3
What does it mean for a chemical reaction to be exothermic?