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Thermo Chemistry Review: Key Concepts and Problem Solving

Explore fundamental concepts of thermochemistry, including reactions, enthalpy, heat transfer, and phase changes. Test your knowledge with practice problems and detailed solutions.

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Thermo Chemistry Review: Key Concepts and Problem Solving

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  1. Warm-up 1: Thermo (Review) 1) How many protons, neutrons, and electrons does lithium-7 have? Atomic number? Mass number? 2) What are the formulas for each: • Carbon hexahydride • Copper (III) oxide • Sulfuric acid • Zinc nitrate 3) How many liters of carbon dioxide gas would you have if you have 20 grams at STP?

  2. Warm-Up 2: Thermo 1) Label each letter. 2) What type of reaction is this? How do you know? 3) If the energy of the reactants is 65 J and the energy of the products is 100 J, what is the enthalpy? 4) What type of reaction is favored in nature?

  3. Warm-Up 3: Thermo 1) Tell what each letter in the diagram stands for: 2) Why doesn’t temperature change during a phase change? 3) If 150 grams of liquid water is heated from 25oC to 80oC, how much heat had to be added? 4) If 85 grams of water freezes to ice, how much heat was released? E H C Temp. G P F Y Time

  4. Warm-up 3 Answers 3) q = mC∆T q = (150 g)(4.18 J/goC)(80o – 25oC) q = 34,485 J 4) q = mHf q = (85 g)(334 J/g) q = 28,390 J  - 28,390 J

  5. Warm-up 4: Thermo 1) How much heat would be released if 60 grams of a liquid at 45oC turns into ice at -25oC? 2) How much heat is absorbed if 75 grams of ice at -30oC is heated until it is steam that is 140oC?

  6. 1) How much heat would be released if 60 grams of a liquid at 45oC turns into ice at -25oC? 3 steps: (1) cool the liquid, (2) freeze it, (3) cool the solid (1) Cooling a liquid  q = mC∆T q = (60 g)(4.18 J/goC)(0o – 45o) q = -11,286 J (2) Freezing  q = mHf q = (60g)(334J/g) q = 20,040 J  -20,040 J (3) Cooling the solid  q = mC∆T q = (60 g)(2.05 J/goC)(-25o – 0o) q = -3075 J Total heat = (-11,286) + (-20,040) + (-3075) = -34,401 J

  7. 2) How much heat is absorbed if 75 grams of ice at -30oC is heated until it is steam that is 140oC? 5 steps! q = (75 g)(2.05 J/goC)(0o – -30o) q = 4612.5 J q = (75 g)(334 J/g) q = 25,050 J q = (75 g)(4.18 J/goC)(100o – 0o) q = 31,350 J q = (75 g)(2260 J/g) q = 169,500 J q = (75 g)(2.02 J/goC)(140o – 100o) q = 6060 J Total q = 236,572.5 J

  8. Warm up 5: Thermo 1) What is calorimetry? 2) If 500 grams of water at 80oC loses 200 J of heat, what is the final temperature of the water? 3) An unknown substance with a mass of 25 grams absorbs 179.4 J of heat and its temperature changes by 8oC. What is the substance?

  9. Warm-up 5 Answers • 2) If 500 grams of water at 80oC loses 200 J of heat, what is the final temperature of the water? q = mCp(Tf – Ti) -200 J = (500g)(4.18J/goC)(Tf – 80oC) Tf = 79.9oC

  10. Warm-up 5 Answers 3) An unknown substance with a mass of 25 grams absorbs 179.4 J of heat and its temperature changes by 8oC. What is the substance? q = mCpΔT 179.4 J = (25g)(Cp)(8oC) Cp = 0.897 J/goC  Aluminum

  11. Warm-up 6: Thermo 1) Decide if each of the following shows an increase in entropy or a decrease: • Freezing • Microwaving soup • Decomposition of water • Condensation 2) Exactly 40 grams of a metal can absorb 800 J of energy, and in the process, heats from 90oC to 128.2oC. What is the metal? 3) What is the final temperature if 80 grams of water starts at 75oC and gives off 1600 J of energy 4) How much energy is released if 25g of steam at 110oC is converted to ice at -8oC?

  12. 2) Exactly 40 grams of a metal can absorb 800 J of energy, and in the process, heats from 90oC to 128.2oC. What is the metal? q = mC∆T 800 J = (40g)(C)(128.2o – 90o) C = 0.523  Titanium 3) What is the final temperature if 80 grams of water starts at 75oC and gives off 1600 J of energy q = mC∆T -1600J = (80g)(4.18J/goC)(Tf – 75o) Tf = 70.2oC

  13. 4) q = (25g)(2.02J/goC)(100 – 110oC) = -505 J q = (25g)(2260J/g) = -56500 J q = (25g)(4.18J/goC)(0 – 100oC) = -10,450 J q = (25g)(334J/g) = -8350 J q = (25g)(2.05J/goC)(-8 – 0oC) = -410 J q total = -76,215 J

  14. Thermo Warm-up 1)What does it mean when a reaction is at equilibrium? 2)Write the equilibrium expression for the following reaction: 2H2(g) + O2(g)  2H2O (l) 2) Draw an energy diagram for an exothermic reaction and label the following: • Energy of the reactants • Energy of the products • Enthalpy • Activation energy • What it would look like if a catalyst was added.

  15. Warm up 7: Thermo 1) What is LeChatlier’s principle? 2) For each situation, describe which way the reaction would shift, if it is an exothermic reaction. a) Adding products. b) Heating it. c) Taking away reactants. d) Adding reactants. e) Taking away products. 3) In general, which way does the reaction shift if you increase the pressure?

  16. Warm up 8: Thermo 1) How much energy is involved if you heat a 20 gram piece of ice from -15oC to liquid water at 30oC? 2) Under what conditions is a reaction always spontaneous? 3) Sketch an energy diagram for an exothermic reaction and label as much as you can. 4) Sketch a heating curve and label as much as you can. 5) How would an endothermic reaction feel if you touched the outside of the test tube?

  17. Warm up 8 Answers 1) q1 = mCΔT q1 = (20g)(2.05J/goC)(0oC -15oC) q1 = 615 J q2 = mΔHfusion q2 = (20g)(334J/g) q1 + q2 + q3 = 9803 J q2 = 6680 J q3 = mCΔT q3 = (20g)(4.18J/goC)(30oC – 0oC) q3 = 2508 J

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