Chemistry Test Chemical Reactions 2 — Questions and Answers
Question 1: What type of reaction occurs when iron rusts in the presence of oxygen and water?
- Decomposition
- Synthesis
- Oxidation-reduction (Correct answer)
- Double displacement
Correct answer: Oxidation-reduction
Rusting is an oxidation-reduction (redox) reaction where iron loses electrons to oxygen, forming iron oxide.
Question 2: In the reaction 2H₂O₂ → 2H₂O + O₂, what is the role of MnO₂ if added?
- Reactant
- Product
- Catalyst (Correct answer)
- Inhibitor
Correct answer: Catalyst
MnO₂ acts as a catalyst, speeding up the decomposition of hydrogen peroxide without being consumed.
Question 3: Which of the following is an example of a synthesis (combination) reaction?
- CaCO₃ → CaO + CO₂
- 2Na + Cl₂ → 2NaCl (Correct answer)
- AgNO₃ + NaCl → AgCl + NaNO₃
- Zn + 2HCl → ZnCl₂ + H₂
Correct answer: 2Na + Cl₂ → 2NaCl
2Na + Cl₂ → 2NaCl is a synthesis reaction because two elements combine to form a single compound.
Question 4: What happens to the rate of a chemical reaction when the temperature is increased?
- It decreases because molecules move slower
- It stays the same regardless of temperature
- It increases because molecules collide more frequently and with more energy (Correct answer)
- It decreases because activation energy increases
Correct answer: It increases because molecules collide more frequently and with more energy
Higher temperature gives molecules more kinetic energy, increasing both collision frequency and the fraction of collisions with sufficient energy to react.
Question 5: In a single displacement reaction, which species is replaced?
- The solvent
- A less reactive element is displaced by a more reactive one (Correct answer)
- A more reactive element is displaced by a less reactive one
- Both elements exchange partners
Correct answer: A less reactive element is displaced by a more reactive one
In single displacement, a more reactive element displaces a less reactive element from its compound.
Question 6: What is the term for the minimum energy required to start a chemical reaction?
- Enthalpy
- Entropy
- Activation energy (Correct answer)
- Bond dissociation energy
Correct answer: Activation energy
Activation energy is the minimum energy colliding particles must have for a reaction to occur.
Question 7: Which observation best indicates that a chemical reaction has occurred?
- Ice melting into liquid water
- Salt dissolving in water
- A gas being produced when vinegar is added to baking soda (Correct answer)
- Sugar dissolving in hot tea
Correct answer: A gas being produced when vinegar is added to baking soda
Gas production (CO₂) when vinegar reacts with baking soda signals a new substance has formed, indicating a chemical reaction.
Chemistry Test Chemical Reactions 2
What type of reaction occurs when iron rusts in the presence of oxygen and water?