AP Chemistry Lab #13



AP Chemistry Lab #14: Reaction Kinetics Name________________________

Date __________ Period ______

Introduction

The purpose of this experiment is to determine the rate law and activation for a specific reaction. The reaction is as follows

A + B + C -------> Products

125 mL Erlenmeyer flask stopwatch or clock thermometer

Droppers starch solution hot water bath

Solution A (1.00 M) Solution B (2.00 M) Solution C (catalyst)

(1.00 M)

I. Safety Concerns:

* Please wear your goggles and aprons the entire lab period.

* Solution A is toxic by ingestion, corrosive and a strong oxidizer.

* Solution B is toxic by ingestion.

* Solution C is toxic by ingestion, body irritant.

II. Procedure:

1. You will be given 100 mL of Solutions A, B and C.

2. In one flask have a volume of Chemical A and add 10 drops of starch(use this amount of starch for each trial). Use no more than 25 mL.

3. In another flask have a volume of Chemical B and 10.00 mL of Chemical C(Use this amount of Chemical C for every trial. Use no more than 25 mL

4. Make sure the total volume is the same for all trials perhaps 40 mL.

4. Now mix the chemicals and record the time in seconds the reaction turns a blue or black color. Make up four experiments with various volumes.

5. Place a thermometer in the 125 mL flask and note the temperature.

6. Measure out the volumes of A, B, C exactly like your first experiment and place the flasks in the 40(C water for three minutes. Now mix the solutions in the 125 mL flask in the hot water bath and record the temp as you are timing.

Table 1: Volumes Used

|Experiment Number |Vol of A (mL) |Vol of B (mL) |Vol of C (mL) |

| | | | |

|1 | | |10.00 |

| | | | |

|2 | | |10.00 |

| | | | |

|3 | | |10.00 |

| | | | |

|4 | | |10.00 |

| | | | |

|5 | | |10.00 |

III. Calculations

1. Determine the Molarity of A, B and C in Table 2 by using M1V1 = M2 V2

2. Calculating the Relative Rate of Reaction

Reaction rates are expressed in the units of Molarity/time (time is measured in seconds in this lab.) Since solution C is the “timer” in these reactions, the rate can be expressed as the moles of Solution C consumed per liter divided by the time (in seconds) it takes for the color to change. This gives a relative rate for the reaction.

3. Set up Rate equations for the different experiments to determine the orders with respect to A and B.

Table 2: Reaction Rates

|Experiment No. |Molarity of A |Molarity of B |Molarity of C |Time |Rate (M |Temp |

| |(mol/L) |(mol/L) |(mol/L) |(sec) |of C /s) |(C |

| | | | | | | |

|1 | | | | | | |

| | | | | | | |

|2 | | | | | | |

| | | | | | | |

|3 | | | | | | |

| | | | | | | |

|4 | | | | | | |

| | | | | | | |

|5 | | | | | | |

In the space below, show how you calculated the molarity of A and of B-. You only need to show the calculations for run #1.

In the space provided below, show how you determined the orders for each reactant.

What is the order with respect to A? _____

What is the order with respect to B? ______

Write the rate law for this reaction here: ____________________________

Calculate the value of the specific rate constant, k, for runs 1-4. Determine an average value for the specific rate constant at room temperature. SHOW YOUR WORK BELOW AND LABEL THE CORRECT UNITS!! (The subscripts refer to the experiment number).

k1 = ________ k2 = ________ k3 = __________ k4 = __________

At Room Temperature

Average value of the Specific Rate Constant (kave) at room temperature = _________

Average room temperature for Experiments 1 through 4 = ________

At Elevated Temperature

Value of the Specific Rate Constant at the elevated temperature (Run 5) = _________

Elevated temperature (temperature for Experiment 5) = _________

Activation Energy, Ea

Use the average values for k and T at room temperature and use the value for the K in Experiment 5 at the elevated temperature to determine the activation energy. SHOW YOUR CALCULATIONS!! Determine your Activation Energy in kJ/mol

IV. Answer the following Analysis Questions in the spaces provided below.

1. List 2 specific places in your lab procedures where errors could have been made. Explain how these errors would have affected the values of your rate constants.

2. How was your rate constant affected by using a higher temperature in Experiment 5? Explain why the reaction was affected by temperature.

3. The total volume of each reaction was 30.0 mL. Why was it necessary to keep the volume constant for each reaction?

4. How would the rates of the various reactions been affected if you had only used half as much of each of the solutions? How would the rate constants have been affected by using only half as much of each of the chemicals in a particular reaction?

5. How would the activation energy of the reaction have been affected if you used the same amounts of chemicals, but doubled the concentration of each chemical?

IV. Solve the following Review Questions in the spaces provided below.

1. An elementary reaction has the reactant H2O2 breaking down to form H2 and O2. When the concentration of H2O2 is 0.500 M, the initial rate is 0.00832 moles per liter per second (M/s). When the concentration is increased to 1.00 M the rate is 0.06656 M/s. What is the order for the hydrogen peroxide in this reaction?

2. Under certain conditions the reaction N2O4 ( 2 NO2 was studied. It was found that the initial rate of reaction was 3.5 x 10-3 M/s when the concentration of N2O4 was 0.015 mol/L. If the concentration of N2O4 is increased to 0.045 mol/L the rate is 0.0105 mol/L-s. What is the order of N2O4 in this reaction?

3. A reaction has the following rate law: rate = k[A] [B]2. Indicate the order with respect to each species as well as the overall order. Then calculate the total factor by which the rate would increase if each reactant’s concentration were doubled.

4. For the reaction described by the following rate law: rate = k[A] [B]2 [C]-1, indicate the order with respect to each species and the overall order. Then calculate the total factor by which the rate would increase if each reactant’s concentration were doubled.

5. The specific rate constant for the decomposition of NO2 is 0.755 M-1s-1 at 330°C and 4.02 M-1s-1 at 378°C. What is activation energy for the reaction?

6. A reaction has an activation energy of 125 kJ/mol. At 25°C the rate is 5.0 x 105 M/s. If the temperature is decreased to 0°C with all other things being the same, then what is the rate of reaction?

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