**4.1.For the reaction R—>P, the concentration of reactant changes from 0.03 M to 0.02 M in 25 minutes. Calculate the average rate of reaction using units of time both in minutes and seconds.**

**Answer :**

**4.2.In a reaction, 2A —-> Products, the concentration of A decreases from 0.5 mol L ^{-1} to 0.4 molL^{-1} in 10 minutes. Calculate the rate during this interval?**

**Answer :**

**4.3. For a reaction, A + B → Products, the rate law is given by : r = k [A] ^{1/2}[B]^{2}. What is the order of reaction?**

**Answer :**

Rate law(r) = k [A]^{1/2}[B]^{2}

order of reaction = 12+2=212or2.5

**4.4.The conversion of molecules X to Y follows second order kinetics. If concentration of X is increased to three times how will it affect the rate of formation of Y ?**

**Answer :**

The reaction is : X—>Y

According to rate law,

rate = k[X]^{2}

If [X] is increased to 3 times, then the new rate is

rate’ = k[3X]^{2}

rate’ = 9 k [X]^{2} = 9 rate

Thus, rate of reaction becomes 9 times and hence rate of formation of Y increases 9-times.

**4.5. A first order reaction has a rate constant 1.15 x 10 ^{-3} s^{-1}. How long will 5 g of this reactant take to reduce to 3 g?**

**Answer :**

**4.6.Time required to decompose SO _{2}Cl_{2} to half of its initial amount is 60 minutes. If the decomposition is a first order reaction, calculate the rate constant of the reaction.**

**Answer :**

For 1st order reaction,

**4.7. What will be the effect of temperature on rate constant?**

**Answer :**

In general, the rate constant for a reaction nearly becomes double with about 10° rise in temperature because of the fact that the effective collisions become almost double. The exact dependence of the reaction rate on temperature is given by Arrhenius equation; k=Ae−Ea/Rt.

Where A is the Arrhenius factor or the frequency factor. It is also called pre exponential factor. It is a constant specific to a particular reaction. R is gas constant and Ea is activation energy measured in joules/mole (J mol^{-1}).

**4.8.The rate of the chemical reaction doubles for and increase of 10 K in absolute temperature from 298 K. Calculate E _{a}.**

**Answer :**

**4.9.The activation energy for the reaction, 2 HI(g) —-> H _{2}+I_{2} (g) is 209.5 k J mol^{-1} at 581 K.Calculate the fraction of molecules of reactants having energy equal to or greater than activation energy?**

**Answer :**

Fraction of molecules having energy equal to or greater than activation energy is given by: