Answer Key Lesson 1-7 PDF

## LESSON 1 ### SHOW ME WHAT YOU KNOW! 1. An environmental chemist is studying data for the reaction between N₂ and O₂ gasses shown below. The concentration of nitrous oxide increases by 0.45M over a period of three minutes. What is the reaction rate of nitric oxide in M/s? N...

## LESSON 1 ### SHOW ME WHAT YOU KNOW! 1. An environmental chemist is studying data for the reaction between N₂ and O₂ gasses shown below. The concentration of nitrous oxide increases by 0.45M over a period of three minutes. What is the reaction rate of nitric oxide in M/s? N_2(g) + 2O_2(g) → 2NO_2(g) + 0.45M = 0.0025M/S 180S 2. A chemist studies the reaction of lithium and nitrate ions. At the beginning of the reaction they have 5g of lithium ions, 10g of nitrate ions, and no lithium nitrate. 30 seconds later after the reaction is complete the chemist measures that there is 0g of lithium ions, 5g of nitrate ions, and 5g of lithium nitrate. Calculate the reaction rate for each species given the reaction: Li⁺ + NO₃^- → LiNO₃ | Species | Rate | Units | |---|---|---| | Li⁺ | -5g | g/s | | NO₃^- | +5g | g/s | | LiNO₃ | +5g | g/s | 3. For the reaction below, what are two ways that a reaction rate could be measured? Pay attention to states! Cu(s) + 4H⁺(aq) + 4NO₃^-(aq) → Cu⁺²(aq) + 2NO₃^-(aq) + 2NO₂(g) + 2H₂O(l) * Mass * Concentration * Pressure 4. The decomposition of NO₂ produces NO and O₂ according to the reaction below. The data in the chart was collected during the reaction. Calculate the reaction rate for each species during a time period of 400s. 2NO_2(g) → 2NO_(g) + O_2(g) | Time (s) | [NO₂] (mol/L) | [NO] (mol/L) | [O₂] (mol/L) | |---|---|---|---| | 0.0 | 0.100 | 0.00 | 0.00 | | 100 | 0.066 | 0.034 | 0.017 | | 200 | 0.048 | 0.052 | 0.026 | | 300 | 0.038 | 0.062 | 0.031 | | 400 | 0.030 | 0.070 | 0.035 | | Species | Rate | Units | |---|---|---| | NO₂ | -0.07M | M/s | | NO | +0.07M | M/s | | O₂ | +0.035 M | M/s | ## LESSON 2 ### SHOW ME WHAT YOU KNOW! 1. Calculate the average rate of reaction for Substance A and Substance B over the full 500 seconds of the reaction. * **Substance A:** -1.650M / 500s = -0.0033M/s * **Substance B:** +1.650M / 500s= +0.0033M/s a) Is species A a product or a reactant? Explain your reasoning. Species A is a *reactant* because its concentration decreases over time, indicating that it is being consumed in the reaction. b) Is species B a product or a reactant? Explain your reasoning. Species B is a *product* because its concentration increases over time, indicating that it is being produced by the reaction. ## LESSON 3 ### SHOW ME WHAT YOU KNOW! 1. Find the reaction rate at 150s for both A and B on the graph. * **Substance A:** Using the points (200, 0.4) and (0, 1.25), the rate is: (0.4 - 1.25) / (200 - 0) = -0.00439 g/s. * **Substance B:** Using the points (250, 1.55) and (0, 0.4), the rate is: (1.55 - 0.4) / (250 - 0) = 0.00469 g/s 2. b) Calculate the average rate of reaction for each species from 0-1200s. | Species | Average Rate | Units | |---|---|---| | NO₂ | +0.5M / 1200s | M/s | | O₂ | +0.12M / 1200s | M/s | | N₂O₅ | -0.25M / 1200s | M/s | c) Calculate the instantaneous rate at 600 seconds for each species. * **Average Rate:** Calculated over a specific time interval. * **Instantaneous Rate:** The exact rate at a particular point in time. d) Label which species are reactants, and which are products. * **Reactants:** N₂O₅ * **Products:** NO₂, O₂ ## LESSON 4 ### SHOW ME WHAT YOU KNOW! 1. For the reaction below, the rate of N₂O₅ consumption is 2.4M/hour. 2N₂O₅ → 4NO₂ + O₂ a) What rate is NO₂ formed at? -2.4M/hr N₂O₅ * 4NO₂ / 2N₂O₅ = +4.8M/hr NO₂ b) What rate is O2 formed at? -2.4M/hr N₂O₅ * 1O₂ / 2N₂O₅ = +1.2M/hr O₂ 2. For the reaction below, write the coefficients in the rate expression for NH₃ compared to each other species in the reaction. 24NH₃ + 5O₂ → 4NO + 6H₂O - Δ[NH₃] / Δt = 4 Δ[O₂] / Δt = 4 Δ[NO] / Δt = 6 Δ[H₂O] / Δt 3. In the reaction below, 4.0 mol of methane combusts in 3.2 seconds. CH₄ + 2O₂ → CO₂ + 2H₂O a) Write out a rate expression for CH₄ compared to each species. - Δ[CH₄] / Δt = -1/2 Δ[O₂] / Δt = Δ[CO₂] / Δt = 1/2 Δ[H₂O] / Δt b) What is the reaction rate of CH₄ in mol/sec? -4.0 mol / 3.2s = -1.25 mol/s c) Calculate the rates of O₂, H₂O, and CO₂ using the CH₄ rate. * **O₂:** -1.25 mol CH₄/s * 2O₂ / 1CH₄ = -2.5 mol O₂/s * **H₂O:** -1.25 mol CH₄/s * 2H₂O / 1CH₄ = +2.50 mol/s H₂O * **CO₂:** -1.25 mol CH₄/s * 1CO2 / 1CH₄ = +1.25 mol/s CO₂ ## LESSON 5 ### SHOW ME WHAT YOU KNOW! 1. Consider the following reaction: Al + 3CuCl → AICI₃ + 3Cu At the start of the reaction there are 38 mol of Al, 125 mol of CuCl, and no products. The amount of Al is measured during the reaction: at 2 seconds 36 mol, at 4 seconds 30 mol, at 6 seconds 22 mol, and at 8 seconds 18 mol. Find the amount of all species using the chart. | Time (seconds) | [Al] | Rate of Change | [CuCl] | [AICI₃] | [Cu] | |---|---|---|---|---|---| | 0 | 38 | - | 125 | 0 | 0 | | 2 | 36 | -2mol/2s | 119 | 2 | 6 | | 4 | 30 | -6mol/2s | 101 | 8 | 24 | | 6 | 22 | -8mol/2s | 77 | 16 | 48 | | 8 | 18 | -4mol/2s | 65 | 20 | 60 | 2. Consider the following reaction: 2KBr + 1Mg → 1MgBr₂ + 2K At the start of the reaction there are 29 mol of Mg, 58 mol of KBr, and no products. The amount of MgBr₂ is measured during the reaction: at 2 seconds 4 mol, at 4 seconds 8 mol, at 6 seconds 14 mol, and at 8 seconds 26 mol. Find the amount of all species using the chart. | Time (seconds) | [MgBr₂] | Rate of Change | [Mg] | [KBr] | [K] | |---|---|---|---|---|---| | 0 | 0 | - | 29 | 58 | 0 | | 2 | 4 | +4 mol/2s | 25 | 50 | 8 | | 4 | 8 | +4 mol/2s | 21 | 42 | 16 | | 6 | 14 | +6 mol/2s | 15 | 30 | 28 | | 8 | 26 | +12 mol/2s | 3 | 24 | 52 | ## LESSON 6 ### SHOW ME WHAT YOU KNOW! 1. Explain how each of the following changes either increases or decreases the rate of a chemical reaction. * **Increasing Concentration:** More particles leads to more collisions, increasing the reaction rate. * **Decreasing Temperature:** Particles have less energy, meaning slower movement, fewer collisions, and a decreased reaction rate. * **Increasing the Volume:** More space for particles to move around in leads to fewer collisions, decreasing the reaction rate. * **Adding a Catalyst:** Allows reactions to occur with less energy, which speeds up the reaction rate. * **Increasing the Pressure:** Less space between particles leads to more collisions, increasing the reaction rate. * **Decreasing the Surface Area:** Less sites for reactions to occur on leads to a decreased reaction rate. ## LESSON 7 ### SHOW ME WHAT YOU KNOW! 1. What is an activated complex/transition state? A temporary "in between" arrangement of atoms as reactants transition to products. 2. The heat content (enthalpy) of reactants is 45kJ. The heat content (enthalpy) of products is 68kJ. What is the enthalpy of the reaction? Is it exothermic or endothermic? * ΔΗ = 68kJ - 45kJ = +23kJ; This reaction is *endothermic* because ΔH is positive, meaning heat is absorbed during the reaction. 3. On the following 2 diagrams label the following: * Reactants * Products * Activated complex * Activation energy * Change in enthalpy * If the reaction is exothermic or endothermic * **Exothermic Reaction:** Energy is *released*, the products are at a *lower energy level* than the reactants. * **Endothermic Reaction:** Energy is *absorbed*, the products are at a *higher energy level* than the reactants. 4. Using the diagram above, answer the following questions: * **a) Is the reaction endothermic or exothermic?** Exothermic, because the products are at a lower energy level than the reactants. * **b) Which letter represents the total energy the reactants have?** B * **c) Which letter represents the total energy the products have?** F * **d) Which letter represents the change in enthalpy of the reaction?** D * **e) Which letter represents the activation energy of the reaction?** A * **f) Which letter represents the total energy of the activated complex?** E * **g) If a catalyst were added, which letter would change?** A and C; a catalyst would lower the activation energy. 5. Using the diagram to the right, answer the following questions: * **a) What is the energy of the reactants?** 80kJ * **b) What is the energy of the products?** 160kJ * **c) What is the change in enthalpy?** +80kJ * **d) What is the activation energy?** 160kJ * **e) What is the energy of the transition state?** 240kJ * **f) Is the reaction endothermic or exothermic?** Endothermic because ΔH is positive. 6. Using the diagram to the right, answer the following questions: * **a) What are the reactants?** X₂ + Y₂ * **b) What is the energy of the reactants?** 50kJ * **c) What are the products?** 2XY * **d) What is the energy of the products?** 100kJ * **e) What is the activation energy?** 160kJ * **f) What is the change in enthalpy?** +50kJ * **g) What is the transition state species?** X₂Y₂ * **h) What is the energy of the transition state?** 150kJ * **i) Would this reaction be faster or slower than the one above?** Faster, it has a smaller activation energy. 7. Use the adjacent diagram to answer the following questions: * **a) What is the energy of the reactants?** 100kJ * **b) What is the energy of the products?** 25kJ * **c) What is the energy of the activated complex?** 250kJ * **d) What is the enthalpy change for this reaction?** -75kJ * **e) What is the activation energy of the reaction?** 150kJ * **f) Is this reaction endothermic or exothermic?** Exothermic because ΔH is negative. 8. Use the adjacent diagram to answer the following questions: * **a) What is the energy of the reactants?** 35kJ * **b) What is the energy of the products?** 15kJ * **c) What is the energy of the activated complex?** 45kJ * **d) What is the enthalpy change for this reaction?** -20kJ * **e) What is the activation energy of the reaction?** 10kJ * **f) Is this reaction endothermic or exothermic?** Exothermic because ΔH is negative. 9. Which of the reactions from questions 7 and 8 would be faster? Which would be slower? Explain why. Reaction #8 would be faster because it has a smaller activation energy. ## LESSON 8 ### SHOW ME WHAT YOU KNOW! 10. A reaction happens between reactants A and B to produce product C. We know that the potential energy of the reactants is 200kJ. The activation energy of the reaction is 250kJ. The potential energy of the resulting product is 100kJ. Use this information to respond to the following questions: a) Draw the potential energy diagram of this reaction on the empty graph below. Remember to label the following: * Axis Names * Y-axis Values * Activation Energy * Activated Complex * Reactants * Products b) Use a dashed line to show what would happen if a catalyst was added. c) Calculate the change in enthalpy of the reaction. -100kJ d) Is this reaction endothermic or exothermic? Exothermic because ΔH is negative.