1. Powder sugar dissolve faster than crystalline sugar. Why?
2. It takes more time to cook rice at higher altitudes. Explain.
3. What is molecularity of a reaction ? Explain with the help of examples.
4. What is order of reaction? Explain.
5. An exothermic reaction A-> B has an activation energy of 13 kcal/mol of A and energy of the reaction is 44 kcal. Find out the activation energy of the reverse reaction.
6. Enzyme catalysed reaction are faster than metal catalysed reactions. Why?
7. If reactant is taken in excess, what will be the order of the reaction w.r.t. that reactant?
8. The alkaline hydrolysis of ethyl acetate is a reaction of second order while with HCl it is of first order, why?
9. Two reactions have identical values of activation energy. Does this mean that these two reactions have the same rate constant if run at the same temperature. Explain.
10. Gasoline evaporates faster than water. Explain.
Solutions:-
Ans1:- Powder sugar dissolves faster than crystalline sugar because powder sugar had greater surface area than crystalline sugar. Greater the surface area in contact with water, faster will be the rate of dissolution.
Ans2:- At high altitudes, water boils at less than 100°C due to low atmospheric pressure. As a result, the rate of cooking becomes less due to decrease in boiling point of water and it takes more time to cook rice.
Ans3:- Molecularity is the number of atoms, ions and molecules actually taking part with one another simultaneously so as to result into a chemical reaction. It is always a whole number. Molecularity is a theoritical value.
Ans4:- Order of the reaction is the sum of the exponents to which the concentration terms must be raised in the rate law equation. It may be whole number, zero and even a fraction. It is an experimental value and can't be determined from stoichiometry of the equation.
Ans5:- Activation energy for the forward reaction is 13 kcal.
Heat of the reaction, ∆E = 44 kcal
Energy of activation for the reverse reaction,
B-> A = activation energy + ∆E
= 13+44
= 57 kcal
Ans6:- Enzyme catalysed reactions have low activation energy and, so that, enzyme catalysed reactions are faster than metal catalysed reactions.
Ans7:- Zero order.
Ans8:- In the former case, the rate depends on the concentration of both ester and alkali while in later case it depends only upon the concentration of ester. So that, alkalined hydrolysis is second order reaction and acidic hydrolysis is a first order reaction.
Ans9:- The value of A, the frequency factor and effectiveness of collisions can be different for each reaction even if their temperature and activation energy's value are the same. So, the two reactions can not have the same rate constants under such conditions.
Ans10:- Activation energy for evaporation of gasoline is less than that of evaporation of water. So, gasoline evaporates faster than water.