Rates+of+Reaction

Thank you Ali! ~Ms. Fradkin

1) For the following process it takes an hour to cook a chicken in the oven and ten minutes to marinate. Which one is the rate limiting step and why? Ans/ Cooking the chicken; because the cooking step is slower than marinating. And marinating is too fast to cookig that it becomes insignificant to the overall reaction.

2) What role does the kinetic energy play in the Transition State Theory? Ans/ The kinetic energy gets transferred into potential energy when the reactants collide.

3) What formula is used to calculate the rate of change of A with respect to time? Ans/ Rate fo reaction= ∆[A] /∆t in(mol/Ls)

4) (a)In a chemical reaction the the concentration of the reactants decreases from 0.8 to 0.2 in 10s. (b)Will the average rate of reaction at 5s be equal to the average rate of reaction in 10s? Ans/ (a) (0.2-0.8)/10 =-0.06 mol/Ls ; (b) No.

5) How does a catalyst increase the rate of a reaction? Ans/ It increases the rate of the reaction by providing an alternative mechanism with a lower activation energy. Thus the activated complex has a lower energy.

6) Write down the rate law equation. What does k represent in the equation? Does it remain constant all the time? If not what kind of factors affect the value of k? Ans/ Rate=k[A]^m [B]^n ; k represents the rate constant. There is a different rate constant for each reaction at different temperatures.

7) What is the overall reaction order when rate is k[A]^3[B]^5? Ans/ Order eight.

8) What kind of reaction in a potential energy diagram has a lower energy level at the beginning of the reaction, endothermic or exothermic? Ans/ Endothermic.

9) What is the overakll order of the following equation R=k[A]^2[B] Ans/ Three.

10) In a potential energy diagram for an exothermic reaction do the reactants or products have a higher potential energy? Will the raection rate be positive or negative? Ans/*The reactants will have a higher potential energy than the products. *Since energy is being released the enthalpy change of the overall reaction will be negative.

11) Why does only the rate of the rate limiting step affect the rate of the overall reaction? Ans/ The rate determining step is much slower than the other elementary reactions. There will be a surplus of products from other reactions end thus only the rate of the slowest reaction will affect the overall rate of the reaction.

12) What does the secant line on a concentration-time graphrepresent and what does the tangent-line represent? Ans/ Secant-line=Average rate ; Tangent-line=Instantaneous rate.

13) According to collison theory, what happens to the reacting particles when the concentration of the reactants increase? Ans/ There will be an increased number of collisions per second.

14) Why does the catalyst not affect the ∆H of a reaction? Ans/ Because it is not consumed by the reaction and ∆H is only dependent on the difference between the products and reactants.

15) What is the difference between an overall reaction and elementary reaction? Ans/ Elementary reaction involves a single molecular event, it cannot be broken down into similer steps. The overall reaction is the result of all the elementary steps.

16) Which of the following is not a method to measure reaction rates? a) Measuring volume. b) Monitoring colour. c) Mass and pH. d) Measuring surface area. e) Measuring pressure. Ans/ D

17) Why is it that heating a solution and increasing its concentration affect reaction rates in the same way? Ans/ Kinetic energy increases to achieve more collisions so there will be a higher chance of successful reaction.


 * Note: There are 3 graphs not included in this page.**