Effect of temperature, Arrhenius equation, activation energy
- The rate of a reaction quadruples when temperature changes from 27^°C to 57^°C. Calculate the energy of activation.Given R = 8.314 J K^-1 mol^-1, log 4 = 0.6021 Answer: 2. 38.04 kJ/mol Key idea: logk₂/k₁=E_a/2.303RT₂-T₁/T₁T₂ . T₁=300 K, T₂=330 K, k₂/k₁=4 . E_a=2.303×8.314×0.6021×300×330/30≈38046\ J/m... 1
- Activation energy of any chemical reaction can be calculated if one knows the value of Answer: 1. rate constant at two different temperatures. Key idea: from the Arrhenius equation, logk₂/k₁=E_a/2.303R(1/T₁-1/T₂) . Knowing k at... 1
- Which plot of ln k vs 1/T is consistent with Arrhenius equation? Answer: 1. [graph option 1, see figure] Key idea: ln k=ln A-E_a/R·1/T , a straight line with negative slope -E_a/R and positive intercept ln... 1
- Given below are two statements : one is labelled as Assertion A and the other is labelled as Reason R :Assertion A : A reaction can have zero activation energy.Reasons R : The minimum extra amount of energy absorbed by reactant molecules so that thei… Answer: 1. A is false but R is true. Key idea: Activation energy is the extra energy reactants must absorb to reach the threshold energy: E_... 1
- The slope of Arrhenius Plot ( k v/s 1/T) of first order reaction is -5×10^3 K. The value of E_a of the reaction is. Choose the correct option for your answer.[Given R=8.314 J K^-1mol^-1] Answer: 1. 41.5 kJ mol ⁻¹ Key idea: Arrhenius equation ln k=ln A-E_a/RT ; slope of ln k vs 1/T is -E_a/R . E_a=-slope× R=5×10³×8.314=41570\... 1
- For a reaction A→B, enthalpy of reaction is -4.2 kJ mol^-1 and enthalpy of activation is 9.6 kJ mol^-1. The correct potential energy profile for the reaction is shown in option. Answer: 2. [graph option - see figure] Key idea: Δ H<0 means the product B lies below reactant A; activation enthalpy 9.6 kJ/mol means the p... 1
- The addition of a catalyst during a chemical reaction alters which of the following quantities ? Answer: 4. Activation energy Key idea: a catalyst provides a different path with a lower activation energy. It does not change the state fun... 1