The role of a catalyst in a chemical reaction is to:
A. Provide an alternative pathway with lower activation energy
B. Decrease the enthalpy change
C. Increase the equilibrium constant
D. Increase the temperature of the reaction
Answer: Option A
Solution (By JKSSB Mock Tests)
A catalyst lowers the activation energy (Ea) by providing an alternative reaction mechanism, thereby increasing the rate of both forward and reverse reactions equally. It does not affect the equilibrium constant, enthalpy change (ΔH), or the position of equilibrium. It remains chemically unchanged after reaction. Positive catalysts speed up, negative catalysts slow down. Enzymes are biological catalysts.
Explanation:
Bakelite (phenol-formaldehyde resin) is thermosetting; once molded, it cannot be reshaped by heating. Polythene, nylon, PVC are thermoplastics, which can be repeatedly softened by heat.
Explanation:
Cetane number measures ignition quality of diesel fuel; higher cetane means easier ignition. Diesel has high cetane (40-55). Petrol has octane number. Methane is gas.
Explanation:
Atomic radius decreases across a period due to increasing nuclear charge. Sodium (Na) is the first element in period 3, thus it has the largest atomic radius. Argon (noble gas) has the smallest (though noble gas radii are van der Waals and larger than covalent, but still trend is decreasing). For metals, Na > Mg > Al; non-metals further smaller.
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