Student Worksheet for Kinetics

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Rhoda Rosaline Hart
5 years ago
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1 Student Worksheet for Attempt to work the following practice problems after working through the sample problems in the videos. Answers are given on the last page(s). Relevant Equations Average Reaction Rate: quantity t Specific Rate = k[a] Rate = k[a] m [B] n k 2 = ( [A 2] k 1 [A 1 ] )m Rate Order = m+n in [A] m [B] n Zero Order Half Life = t 1/2 = 1 All Other Half life= t 1/2 = ka 0 Zero Order Reactions = [A] = [A 0 ] kt First Order Reactions = ln[a] = -kt + ln[a 0 ] Second Order Reactions = 1 [A] = kt + 1 [A 0 ] k Where, t is time, k is the rate constant, A and B are the reactants, A0 is the original amount of reactant, and m and n are the orders that sum to the reaction order Supercharged Science 1

2 1. Explain the significance of the peak of an energy diagram. Relate this to how an enzyme works. 2. The following data is collected during research of CH 3 CHO + HCl CH 3 CHClOH. What is the reaction order? Trial Initial [CH 3 CHO] Initial [HCl] Rate * * * How much time passed in Experiment 2, assuming that all of the HCl was consumed? 4. Write the expression rate reaction for the following equation: CH O 2 CO H 2 O 2017 Supercharged Science 2

3 5. If the rate of appearance of HCl by the following equation is 0.53 M/sec, what is the rate of disappearance of CHCl 3? CHCl CH 3 OH 3 HCl + CH(CH 3 O) 3 6. The rate law for the following reaction is rate = k[h 2 ][N 2 ]. If the rate is 6.25 x 10-2 M/s when [H 2 ] = M and [N 2 ] = 0.50 M, calculate the rate when [H 2 ] = M and [N 2 ] = 0.10 M. (Hint: find the rate constant k). N H 2 2 NH 3 7. If the concentration of reactants is tripled and the rate of reaction increases by 9x, what is the order of the reaction? How do you know? 8. What is the half-life for a first order reaction if the initial concentration of reactant is 1.57M and after 58.6 seconds the concentration has dropped to 0.75M? 2017 Supercharged Science 3

4 9. What is the half-life for a second order reaction if the initial concentration of reactant is 2.50M and after 69.2 seconds the concentration has dropped to 1.78M? 10. What is the half-life for a zero order reaction if the initial concentration of reactant is 1.45M and after 72.4 seconds the concentration has dropped to 0.93M? 11. What percentage of an original 90 gram sample will be remaining after 5 half lives? 12. The following data is collected while researching the reaction of C 2 H 4 + Cl 2 C 2 H 4 Cl 2. What is the reaction order? Experiment [C 2 H 4 ] [Cl 2 ] Rate (M/s) M 0.5M M 1.0M M 1.0M Supercharged Science 4

5 13. What is the value of the rate constant in your answer to number 11? 14. What is the rate of the reaction for the equation HNO + O 2 HNO 3 if the rate constant is 2.85*10 2 M/sec, and [HNO] is 0.2M and [O 2 ] is 0.25M? 15. The determined rate constant for the decomposition of 0.35M N 2 O 5 is 3.5*10-6. What concentration of N 2 O 5 will be left after 30 seconds if 2L of the solution is mixed with 1 L of water? 2017 Supercharged Science 5

6 1. Explain the significance of the peak of an energy diagram. Relate this to how an enzyme works. The peak of the energy diagram annotates when reactants are in their transition state (no longer reactants, but not quite products). Energy is being released and consumed at the same time. When an enzyme is used, it puts its substrates at the transition state. Hence, the entire reaction does not need to happen for the products to be made. This is why the energy required is much lower when an enzyme is present. 2. The following data is collected during research of CH 3 CHO + HCl CH 3 CHClOH. What is the reaction order? Trial Initial [CH 3 CHO] Initial [HCl] Rate * * *10-3 Beginning with Experiments 1 and 2, the concentration change is with CH 3 CHO. k 2 = ( [A 2] k 1 [A 1 ] )m = = ( )m 2 = 2 m m = 1, so the reaction of CH 3 CHO is first order. Continuing to Experiments 2 and 3, the concentration of HCl changes. k 2 = ( [A 2] k 1 [A 1 ] )m = 8.0 = 4.0 ( )m 2 = 2 n n= 1, so the reaction of HCl is also first order. Reaction rate order= m + n = = 2 nd order reaction 3. How much time passed in Experiment 2 of Question 2, assuming that all of the HCl was consumed? Average rate = Quantity t t = 1 M M/s = 500 seconds 2017 Supercharged Science 6

7 4. Write the expression rate reaction for the following equation: CH O 2 CO H 2 O - [CH 4] T = [O 2 ] = [CO 2] = 1 T T 2 [H 2 O] T 5. If the rate of appearance of HCl by the following equation is 0.53 M/sec, what is the rate of disappearance of CHCl 3? [HCl] = [CHCl 3] 3 T 1 T = = 0.18M/sec CHCl CH 3 OH 3 HCl + CH(CH 3 O) 3 Multiply both sides by 1 T to get [CHCl 3 ] by itself 6. The rate law for the following reaction is rate = k[h 2 ][N 2 ]. If the rate is 6.25 x 10-2 M/s when [H 2 ] = M and [N 2 ] = 0.50 M, calculate the rate when [H 2 ] = M and [N 2 ] = 0.10 M. (Hint: find the rate constant k). Rate= 6.25*10-2 M/s = k(0.075)(0.50) N H 2 2 NH 3 k= ( ) = 1.67 M-1 s -1 Now, use the constant to find the new rate. Rate= 1.67*0.035*0.10 = 5.8*10-3 M/s 7. If the concentration of reactants is tripled and the rate of reaction increases by 9x, what is the order of the reaction? How do you know? It is a 2 nd order reaction, and be found using: [A] m = k. In this case, 3 m = 9 m= 2 because 3 squared equals 9. Note, you should have used this method for Question Supercharged Science 7

8 8. What is the half-life for a first order reaction if the initial concentration of reactant is 1.57M and after 58.6 seconds the concentration has dropped to 0.75M? You must first solve for k, using this formula. ln[a] = -kt + ln[a 0 ] ln0.75 = -k(59.6) + ln1.57 -k = -1.24*10-2 Multiplying both sides by -1 gives the positive k for half-life. t 1/2 = k = = seconds 9. What is the half-life for a second order reaction if the initial concentration of reactant is 2.50M and after 69.2 seconds the concentration has dropped to 1.78M? Like # 7, you have to first solve for k. 1 [A] = kt + 1 [A 0 ] = k = 69.2 k = 69.2 k Multiply both sides by 1 k = = 2.34*10-3 M/s t 1/2 = 1 A 0 k t 1/2 = 1 ( ) = seconds 69.2 to isolate k. 10. What is the half-life for a zero order reaction if the initial concentration of reactant is 1.45M and after 72.4 seconds the concentration has dropped to 0.93M? [A] = [A 0 ] kt k= [A 0] [A] t 2017 Supercharged Science 8

9 = = 7.18*10-3 M/s t 1/2 = [A 0] 2k = = seconds 11. What percentage of an original 90 gram sample will be remaining after 5 half lives? Divide by 2, 5 times. 90/2 = 45 45/2 = /2 = / 2 = /2 = 2.81 Percent left= ( 2.81 ) 100 = 3.1% 90 You could have also found out how much is left (the 2.81 g) by using the formula: Original Mass 2 # of half lives 12. The following data is collected while researching the reaction of C 2 H 4 + Cl 2 C 2 H 4 Cl 2. What is the reaction order? Experiment [C 2 H 4 ] [Cl 2 ] Rate (M/s) M 0.5M M 1.0M M 1.0M 27.2 Beginning with Experiments 1 and 2, the concentration change is with Cl 2. k 2 = ( [A 2] k 1 [A 1 ] )m = 6.8 = 3.4 ( )m 2 = 2 m m = 1, so the reaction of Cl2 is first order. Continuing to Experiments 2 and 3, the concentration of C2H4 changes Supercharged Science 9

10 k 2 = ( [A 2] k 1 [A 1 ] )m = 27.2 = ( )m 4 = 2 n n= 2, so the reaction of C 2 H 4 is second order. Reaction rate order= m + n = = 3 rd order reaction 13. What is the value of the rate constant in your answer to number 11? You may choose any of the experiments, but I will use Experiment 1. Rate = k[a] m [B] n 3.5 M/s = k * 0.25 M/s 2 * 0.5 M/s 1 3.5M/s k = ((0.25 M s )2 0.5 M s ) k = 112 M -2 sec What is the rate of the reaction for the equation HNO + O 2 HNO 3 if the rate constant is 2.85*10 2 M/sec, and [HNO] is 0.2M and [O 2 ] is 0.25M? Rate= k[a] m [B] n = 2.85*10 2 * * = M/s 15. The determined rate constant for the decomposition of 0.35M N 2 O 5 is 3.5*10-6. What concentration of N 2 O 5 will be left after 30 seconds if 2L of the solution is mixed with 1 L of water? You must first determine the new molarity. M 1 V 1 = M 2 V 2 M 2 = M 1V 1 V 2 = = 0.35M2L 3L = 0.23M Now, plug these values into the rate equation. Rate= k[a] = 3.5*10-6 * 0.23 = 8.17*10-7 M/sec Now use the average reaction rate to calculate how much decomposed in the time given Supercharged Science 10

11 Average Reaction Rate: quantity t Quantity = t Rate = 30 seconds * 8.17*10-7 M/sec = 2.45*10-5 M You initially had 0.23 mol/l and 2.45*10-5 mol/l decomposed, so you are left with: 0.23M solution 2017 Supercharged Science 11

Student Worksheet for Thermochemistry

Student Worksheet for Thermochemistry Student Worksheet for Attempt to work the following practice problems after working through the sample problems in the videos. Answers are given on the last page(s). Relevant Equations/Information Specific