Chemistry sample questions for entrance exam

Question: 1If the concentration is expressed in moles per litre, the unit of the rate constant for a first order reaction isChoicea) mollitre1sec1 b) mollitre1 c) sec1 d) mol1Correct Answer : cQuestion: 2A reaction AB follows a second order kinetics . Doubling the concentration of A will increase the rate of formation of B by a factor ofChoicea) 2 b) 12 c) 4 d) 14Correct Answer : cHints : Question: 3The rate of constant of first order reaction whose half life is 480 sec isChoicea) 1.44 x 103sec1 b) 1.44 sec1 c) 0.72 x 103sec1 d) 2.88 x 103sec1Correct Answer : aHints :Question: 4The reaction 2H2O2O2 is r =k[H2O2Choicea) Zero order reaction b) First order reaction c) Second order reactiond) Third order reactionCorrect Answer : bQuestion: 5A chemical reaction is catalysed by X. Hence XChoicea) does not affect equilibrium constant of the reaction b) decrease rate constant of the reaction c) decrease enthalpy of reaction d)increases activation energy of the reactionCorrect Answer : aQuestion: 6For the first order reaction with rate constant k, which expression gives the half life period? (initial conc = a)Choicea) in2ka b) 1ka c) 0.693k d) 32ka2Correct Answer : cQuestion: 7The rate constant is given by the equation k=P.ZeeRT. Which factor should register a decrease for the reaction to proceed more rapidly ?Choicea) T b) Z c) E d) PCorrect Answer : pHints :For K to increase, activation energy should decreaseQuestion: 8For a reaction of type A+B products, it is observed that doubling concentration of A cause the reaction rate to be four times as great, but doubling amount of B does not affect the rate. The rate equation isChoicea) Rate =K[A][B] b) Rate =k4A2 c) Rate = K[A2B0 d) Rate = K[A2B2Correct Answer : cHints :Question: 9The reaction N2O5inccl42NO212O2g is the first order in N2O5 with rate constant 6.2 x 104s1. What is the value of rate of reaction when[N2O51.25molL1 ?Choicea) 7.75 x 104 mol L1s1 b) 6.35 x 103 mol L1s1 c) 5.15 x 105 mol L1s1d) 3.85 x 104 mol L1s1Correct Answer : aHints :Rate = K [N2O56.21041.257.75104Question: 10The Arrhenius equation expressing the effect of temperature on the rate constant of the reaction isChoicea) k = e EaRT b) k = EaRT c) k = loge EaRT d) k = A.eEaRTCorrect Answer : dHints :Question: 11If reaction between A and B to give C shows first order kinetics in A and second order in B, the rate equilibrium can be written asChoicea) Rate =k[A][B12 b) Rate =k[A12[B c) Rate =k[A][B2 d) Rate =k[A2BCorrect Answer : cHints :r = k[A2when concentration is doubled r = k[2A2k4[A24rQuestion: 1275% of first order reaction is complete in 30 minutes. What is the time required for 93.75% of the reaction (in minutes) ?Choicea) 45 b) 120 c) 90 d) 60Correct Answer : dHints :Product concentration is zero initially.OH2 50%H275%H287.5%H293.75 .After 4H293.75% reaction is completed. For 75%, 2 H2ie,.2H230H2302Question: 13The time taken for 90% of a first order reaction to complete is approximatelyChoicea) 1.1 times of that of half life b) 2.2 times of that of half life c) 3.3 times of that of half life d) 4.4 times of that of half lifeCorrect Answer : cHints :t90%2.303klogaa0.9a2.303klog102.303kt 1 2 = 2.3030.3010k0.693kt 90 % t 1 2 1 0.3010 3.3 ie.t90%3.3timest12Question: 14The half life period for a first order reaction is 693 seconds. The rate constant of this reaction would beChoicea) 0.1sec1 b) 0.001sec1 c) 0.01sec1 d) 0.0001sec1Correct Answer : cQuestion: 15The order of reaction is decided byChoicea) temperature b) mechanism of reaction as well as relative concentration of reactants c) molecularity d) pressureCorrect Answer : bHints :