Which of the following increases the rate of a chemical reaction?
A. Adding a positive catalyst
B. Using larger pieces of solid reactants
C. Decreasing temperature
D. Decreasing concentration of reactants
Answer: Option A
Solution (By JKSSB Mock Tests)
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:
A catalyst lowers the activation energy barrier by providing a different reaction mechanism. This allows more reactant molecules to have sufficient energy to react. It does not change the thermodynamics (ΔH, equilibrium constant) or get consumed in the reaction. Enzymes are biological catalysts.
Explanation:
Rate ∝ 1/√M. Molar masses: CO₂=44, SO₂=64, CH₄=16, Cl₂=71. Methane has the smallest molar mass, so it diffuses fastest. Graham's law applies.
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