Unit 05Energetics: Review Sheet: Heat and Temperature 1. What is absolute zero? 2. Convert 25C to Kelvin 3. Convert 400 K to Celsius 4. What is the difference between heat and temperature? 5. Can two objects at the same temperature have the same amount of heat? Specific Heat Capacity 6. What is the definition of specific heat capacity? 7. What is the specific heat capacity of water? 8. Why is the specific heat capacity of water higher than that of ethanol? 9. Which requires more energy to change the temperature? a. Gold (C = 0.128 J/g C) or Silver (C = 0.235 J/g C)? b. Water (C = 4.184 J/g C) or ethanol (C = 2.44 J/g C)? 10. Is specific heat capacity a physical or chemical property? Calorimetry 11. 66,938 joules of heat energy is needed to raise the temperature of a 425 g aluminum baking sheet to a baking temperature of 200C? What is the initial temperature of the baking sheet? The specific heat of aluminum is 0.90 J/g 0C 12. The temperature of an iron bar with a mass of 87.0 g is raised from 31C to 543C. In the process, 4900 calories of heat energy were absorbed. What is the specific heat of iron? 13. How is calorimetry used to determine the number of calories in food? 14. More practice problems: pg 525 (#78,79) Phase Changes 15. Pg. 881 (7,8) The following graph is a heating curve for an unknown substance. 100 e d Temp 80 (C) c 60 b 40 20 a time 16. At what temperature is the melting point? 17. At what temperature is the boiling point? 18. Which letter corresponds to a time when a. the solid form of the compound is changing temperature? b. the liquid form of the compound is changing temperature? c. the gas form of the compound is changing temperature? d. The solid is melting e. The liquid is freezing f. The liquid is evaporating g. The gas is condensing 19. If you wanted to calculate the heat associated with the changes in the graph a. When would you use Q = mCT (3 answers)? b. When would you use Q = mHfus? c. When would you use Q = mHvap? Enthalpy, Entropy, Gibbs Free Energy 20. Predict whether the following reactions will be spontaneous: a. CO2(s) CO2(g) b. H2O(l) H2O (s) c. CaCl2 (s) CaCl2 (aq) d. 2H2O(g) H2(g) + O2(g) H = 145 kJ e. 2Mg + CO2 2MgO + C H = -220 kJ f. MgSO48H2O + H2O Mg2+ + SO4 2- + 9 H2O g. A reaction conducted at 900C: H = 135.5 kJ, S = 148.8 kJ h. A reaction has a G that is less than zero i. A reaction has a negative H, and positive S j. A reaction has a positive H, and a negative S k. A reaction has a positive H, and a positive S 21. The thing we measure when we want to determine the average kinetic energy of random motion in the particles of a substance is __________________. 22. The __________________ is used to describe how much energy is produced or used during a chemical change. 23. The __________________ is the energy needed to raise the temperature of a substance by one degree Celsius. 24. The measure of randomness in a system is called __________________. 25. The __________________ is the energy required to boil one mole of a substance, and its symbol is __________________. 26. __________________ reactions require energy in order to take place. 27. A(n) __________________ reaction is one where the products have lower energy than the reactants. 28. Another word for freezing is __________________. 29. __________________ changes take place by themselves, without a continuous supply of energy. 30. __________________ is the amount of energy which a system has to have in order for a chemical change to take place. 31. __________________ is the symbol which stands for the value equal to the enthalpy minus the temperature times entropy. It can be used to determine if a reaction will take place __________________. Word Bank: Heat Specific heat capacity Endothermic Temperature Heat of vaporization Catalyst Exothermic Heat of fusion Enthalpy Fusion Gibbs free energy Heat of reaction Spontaneous Activation energy Entropy Spontaneously Hfus G Hvap Energy Diagrams 32. Draw an energy diagram for a reaction. (label the axis) a. Potential energy of reactants = 350 KJ/mole b. Activation energy = 100 KJ/mole c. Potential energy of products = 250 KJ/mole 33. With a blue pencil show the amount of activation energy required for the exothermic reaction 34. The reverse reaction would be endothermic. Show the activation energy for the endothermic reaction with a green pencil 35. With a red pencil show the enthalpy change 36. Draw a second energy diagram with the same energy levels as in 1. 37. With another color pencil show how the energy of reactants, energy of products, enthalpy change and activation energy would change if a catalyst was used. 38. Is this reaction exothermic or endothermic? 39. How would you determine if it is spontaneous? Essay Questions A. Describe the driving forces of reactions. B. Explain how sweating helps to cool the body. C. What is meant by the heat death of the universe? D. A friend of yours reads that the process of freezing is exothermic. This friend tells you that this can’t be true because exothermic implies “hot”, and ice is cold. IS the process of freezing exothermic? If so, explain it so your friend can understand it. If not, explain why not.