ChemReaX Virtual Lab_ Chemical Kinetics

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University of Illinois, Chicago *

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Chemistry

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Feb 20, 2024

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1/21/24, 10:28 PM ChemReaX Virtual Lab: Chemical Kinetics https://docs.google.com/forms/d/e/1FAIpQLSdAKfwY0SUWyAHkJDbHZdQ56ZJ9F43gZYC_KGGeJ6QX903KIQ/viewscore?viewscore=AE0zAgAHzvpjfOP9YI… 1/11 ChemReaX Virtual Lab: Chemical Kinetics Total points 14/14 Chemical kinetics is the study of reaction rates and is complementary to the thermodynamic considerations of whether a reaction is spontaneous . The rate of a reaction (i.e., how fast it proceeds) at constant temperature depends on the concentrations or partial pressures of the reactants and products, and can be modeled by differential equations called rate laws. There are many different forms of integrated rate laws/models which express the rate of a reaction in terms of the reactant and product concentrations. A generalized integrated reaction rate model used in ChemReaX is: Rate v = k * [R1]^X * [R2]^Y * [R3]^Z, where R1, R2 and R3 are the reactants. The square brackets in our notation denote either concentration (units: moles/L) or partial pressure (units: bars). The reaction order is X+Y+Z, and the rate constant is k. The half-life of any reactant is the time taken for the concentration or partial pressure to reach half its initial value. Steps: Go to the ChemReaX "General Reactions" tab or dashboard on this site or at chemreax.com . Click "Clear All" to reset ChemReaX. Enter the reactants and products for each speci±ed reaction using the searchable dropdown lists. Click "Balance the Equation". Enter the initial concentrations or partial pressures of the reactants and products. Check the "Specify the Reaction Rate Parameters" box at the top right corner, and enter the reaction rate parameters (k, X, Y and Z) -- these are the parameters you will vary in this simulation exercise. After entering appropriate values for these parameters, simulate the reaction by clicking "Run the Reaction". Scroll down to see the simulation results and the ±nal composition (partial pressures in this exercise) of all the reactants and products. Run multiple simulations with parameter variations as needed to answer the questions below. Notation: Pi(X) means the initial partial pressure of gas X; Pf(X) means the ±nal partial pressure of gas X.

1/21/24, 10:28 PM ChemReaX Virtual Lab: Chemical Kinetics https://docs.google.com/forms/d/e/1FAIpQLSdAKfwY0SUWyAHkJDbHZdQ56ZJ9F43gZYC_KGGeJ6QX903KIQ/viewscore?viewscore=AE0zAgAHzvpjfOP9YI… 2/11 1/1 0.42 second 1.87 seconds 6.49 seconds 44.75 seconds 1/1 0.42 second 1.87 seconds 6.49 seconds 44.75 seconds Set up the reaction for the synthesis of hydrogen iodide: H2 (g) + I2 (g) 2HI (g). Set the initial partial pressures: Pi(H2) = 0.5 bar, Pi(I2) = 0.6 bar, Pi(HI) = 0. Set the temperature at 721K, leaving the pressure factor at the default value of 1.0. Set the reaction rates for a zeroth-order reaction: k=1, X=0, Y=0, Z=0. The time taken for the reaction to reach its final state is: * Change the reaction-rate model to first order: k=1, X=1, Y=0, Z=0. The time taken for the reaction to reach its final state is: *

1/21/24, 10:28 PM ChemReaX Virtual Lab: Chemical Kinetics https://docs.google.com/forms/d/e/1FAIpQLSdAKfwY0SUWyAHkJDbHZdQ56ZJ9F43gZYC_KGGeJ6QX903KIQ/viewscore?viewscore=AE0zAgAHzvpjfOP9YI… 3/11 1/1 0.42 second 1.87 seconds 6.49 seconds 44.75 seconds 1/1 0.42 second 1.87 seconds 6.49 seconds 44.75 seconds 1/1 Increases Decreases Change the reaction-rate model to second order: k=1, X=1, Y=1, Z=0. The time taken for the reaction to reach its final state is: * Change the reaction-rate model to third order: k=1, X=2, Y=1, Z=0. The time taken for the reaction to reach its final state is: * Does the time taken to reach the final state increase or decrease with reaction order? *

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1/21/24, 10:28 PM ChemReaX Virtual Lab: Chemical Kinetics https://docs.google.com/forms/d/e/1FAIpQLSdAKfwY0SUWyAHkJDbHZdQ56ZJ9F43gZYC_KGGeJ6QX903KIQ/viewscore?viewscore=AE0zAgAHzvpjfOP9YI… 4/11 1/1 Faster slope earlier, followed by a long slower tail Slower slope earlier, followed by a faster slope Does not change with reaction order 1/1 Takes twice as long to complete the reaction Takes half as long to complete the reaction 1/1 Takes twice as long to complete the reaction Takes half as long to complete the reaction How does the shape of the shape of the response curve (partial pressure vs. time) change with increasing reaction order? * If the rate constant k doubles, what happens to the time taken to complete the reaction? * If the rate constant k is cut in half, what happens to the time taken to complete the reaction? *

1/21/24, 10:28 PM ChemReaX Virtual Lab: Chemical Kinetics https://docs.google.com/forms/d/e/1FAIpQLSdAKfwY0SUWyAHkJDbHZdQ56ZJ9F43gZYC_KGGeJ6QX903KIQ/viewscore?viewscore=AE0zAgAHzvpjfOP9YI… 5/11 1/1 0.2 second 0.23 second 0.35 second 0.4 second 1/1 Yes No Set up the reaction for the synthesis of ammonia: N2 (g) + 3H2 (g) 2NH3 (g). Set the initial partial pressures: Pi(N2) = 1 bar, Pi(H2) = 3 bar, Pi(NH3) = 0. Let the temperature and pressure factor be at the default values of 298.15K and 1.0. Using a first-order rate model (k=1, X=0, Y=1), what is the approximate half-life of H2 based on the kinetics tables produced by ChemReaX: * Does doubling the values of Pi(H2) and Pi(N2) change the half-life of H2 for a first-order reaction? (Note: Ignore any differences beyond 2 decimal places.) *

1/21/24, 10:28 PM ChemReaX Virtual Lab: Chemical Kinetics https://docs.google.com/forms/d/e/1FAIpQLSdAKfwY0SUWyAHkJDbHZdQ56ZJ9F43gZYC_KGGeJ6QX903KIQ/viewscore?viewscore=AE0zAgAHzvpjfOP9YI… 6/11 1/1 Increases as Pi(H2) increases Decreases as Pi(H2) increases Does not change 1/1 Yes No 1/1 Increases Decreases Does not change Change the rate model to second order (k=1, X=0, Y=2; or k=1, X=1, Y=1), and then run a few simulations with various values of Pi(H2), always keeping it 3 times Pi(N2) so that H2 is not a limiting reactant. How does the half-life of H2 respond to changes in Pi(H2) in this second-order reaction? * Would you expect the half-lives of reactants in higher-order reactions to have a similar dependency on initial concentrations or partial pressures? * For the synthesis of ammonia as a second-order reaction (k=0, X=1, Y=1), if Pi(N2) = 1 bar and Pi(H2) is varied between 0.5 bar and 2 bars, does the half life of H2 increase or decrease with increasing Pi(H2)? (Hint: Note that H2 is a limiting reactant, and more N2 is used up as Pi(H2) increases.) *

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1/21/24, 10:28 PM ChemReaX Virtual Lab: Chemical Kinetics https://docs.google.com/forms/d/e/1FAIpQLSdAKfwY0SUWyAHkJDbHZdQ56ZJ9F43gZYC_KGGeJ6QX903KIQ/viewscore?viewscore=AE0zAgAHzvpjfOP9YI… 7/11 1/1 The half life of a reactant always increases as the initial concentration or partial pressure of that reactant increases The half life of a reactant always decreases as the initial concentration or partial pressure of that reactant increases The half life of a reactant may increase or decrease as the initial concentration or partial pressure of that reactant increases, depending on the relative quantities of the other reactants. This content is neither created nor endorsed by Google. - Terms of Service - Privacy Policy Based on the experiments with ammonia synthesis, which of these is a reasonable conclusion for a second or higher order reaction? * Forms