Which of the following increases the rate of a chemical reaction?
A. Decreasing concentration of reactants
B. Using larger pieces of solid reactants
C. Adding a positive catalyst
D. Decreasing temperature
Answer: Option C
Solution (By JKExamLibrary)
A positive catalyst increases reaction rate by lowering activation energy. Decreasing temperature generally slows reactions. Decreasing concentration reduces collision frequency, lowering rate. Larger pieces have less surface area, slower reaction. Other rate-increasing factors: increasing temperature, increasing pressure (for gases), using finely powdered solids, and light for photochemical reactions.
Explanation:
Groups (vertical columns) contain elements with the same number of valence electrons, leading to similar chemical properties. The modern table is based on atomic number; 7 periods exist; noble gases are in Group 18.
Explanation:
HCl is oxidized (Cl⁻ → Cl₂, loss of electrons), so it acts as the reducing agent. MnO₂ is reduced (Mn⁴⁺ → Mn²⁺) and is the oxidizing agent.
Explanation:
Sodium and potassium are highly reactive alkali metals that react vigorously with oxygen and moisture in the air, potentially catching fire. To prevent accidental fires, they are stored immersed in kerosene oil. Magnesium and calcium do not require such extreme storage conditions.
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