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Thermochemistry / Energy Test Review PREAP NAME_______________________________________Period______ To be completed on notebook paper. Number all questions/tasks. You only need to rewrite them if the problem requires it to be solved. Remember the powerpoint notes are online. THIS IS A DAILY GRADE 1) Define: Potential Energy Temperature Exothermic Process Specific Heat Kinetic Energy Chemical Potential Energy Endothermic Reaction Molar Heat of Fusion Heat Endothermic Process Exothermic Reaction 2) Draw a heating curve for water. Label the y axis temperature and the x axis heat (or heat added over time can also be used). Indicate the following by labeling the graph as you see fit. a. On the axis show the temperatures at which water undergoes phase changes b. Melting pt, boiling pt, freezing pt, condensing pt. c. Where temperature remains constant d. Where potential energy is increasing or decreasing (state which one) e. Where kinetic energy is increasing or decreasing (state which one) f. Where solid, liquid, and gas are and where solid-liquid and liquid-gas g. Where the formulas Q=mC∆T and Q=mol • ∆H are applied h. Where the speed of the molecules is not changing i. Where the intermolecular bonds between water molecules are being broken or formed (state which one) j. Where the speed of the molecules is increasing or decreasing (state which one) k. What would be different about a COOLING curve? Be sure you understand which things would change (direction of energy flow) and which things would not (types of energy, boiling pt., etc.) 3) What’s the difference between Heat and Temperature? They are different, but they are related…how? a. Give an example of how they are different. (see powerpoint notes for one if you can’t think of one) 4) Define each of the following phase changes in terms of endothermic and exothermic. State which direction heat energy flows regarding the system and the surroundings. State whether bonds are being broken or formed. State what is happening to kinetic energy and potential energy during the phase change. a)Freezing b)melting c)vaporizing (boiling) d)condensing e)subliming 5) Why does spraying crops with water protect them during freezing cold weather? (see powerpoint notes) Constants: You don’t have to memorize these, just know how / when to use them Specific Heat Constants for water Csolid = 2.11 J/g°C Cliquid = 4.2 J/g°C Cgas = 2.01 J/g°C Molar Heat constants for water Hfusion= 6.02 kJ/mol Hvaporization= 40.65 kJ/mol 6) Equations: a. Rearrange Q=mC∆T to solve for: m= c= ∆T = b. Rearrange Q=mol • ∆H to solve for: mol= ∆H= c. What are the unit(s) of m, C, ∆T, mol, ∆H, and Q? d. Will you use the formula Q=mC∆T during a phase change? e. What temperatures limit the range of the formulas? f. Why is the following incorrect? (its not sig figs) Q = 10.0 g • 4.2 J/g°C • 125°C = 5250J g. Between what temperatures can you use Csolid = 2.11 J/g°C? Cliquid = 4.2 J/g°C? Cgas = 2.01 J/g°C? h. Why is Hvaporization a larger number than Hfusion? How is this related to the length of the flat portions of the heating curve? i. Why does water have a greater amount of heat energy than a piece of lead that is the same temperature and same mass? 7) A very hot 15.0g piece of lead is placed inside a calorimeter with water and the 28.0 g of water are heated from -5°C to 150°C? How many joules of energy are absorbed by the water? 8) How much heat, in joules, is released when 48.0g of steam is cooled from 1350°C to 50.0°C? 9) How much heat, in joules, is needed to change 35.0 grams of ice at 0.0°C to liquid water at 0.0°C? 10) How much heat, in joules, is needed to raise the temperature of 2.5 moles of water from 50.0°C to 75.0°C 11) How many joules are required to boil 140.0 grams of water? 12) How many joules are given off when 145 grams of water are cooled from 35.0°C to -35.0°C 13) A reaction occurs between 78.0g hydrochloric acid and 1.20g calcium that raises the temperature inside the calorimeter from 25.0°C to 78.0°C. The specific heat of the solution is 4.2 J/g°C. The mass of the total solution is 79.20g. Determine the ΔHrxn (in kJ/mol) using Q=mCΔT and Q=molΔHrxn (SHOW WORK) (this is like what we did in the lab) 14) Oxygen is necessary for releasing energy from glucose in organisms. How many kJ of heat are produced when 2.24 mol glucose reacts with an excess of oxygen? C6H12O6(s) + 6O2(g) 6CO2(g) + 6H2O(g) + 2808 kJ/mol (The answer is in the powerpoint notes) 15) Solve the problem below (The answer is in your powerpoint notes labeled as 17.2 sample problem) 16) What is the relationship between Hreaction , Hproducts , and Hreactants? a. What does a -Hreactants reveal? What has more potential energy, the reactants or the products? b. What does a +Hreactants reveal? What has more potential energy, the reactants or the products? 17) What is Hess’s Law? Explain it. 18) Carbon occurs in two forms: graphite and diamond. The enthalpy of combustion of graphite is -393.5 kJ, and that of diamond is - 395.4 kJ. Calculate H for the conversion of graphite to diamond: C(graphite) C(diamond) C(graphite) + O2(g) -> CO2(g) H = -393.5 kJ C(diamond) + O2(g) -> CO2(g) H = -395.4 kJ 19) Given the following reactions and their enthalpy changes, calculate the enthalpy change for the first reaction H2(g) + C(s) + O2(g) -----> HCOOH(l) H=? C(s) + O2(g) ---> CO2(g) H=-394 kJ H2(g) + 1/2 O2(g) ---> H2O(l) H=-286kJ HCOOH(l) + 1/2 O2(g) ---> CO2(g) + H2O(l) H=-275kJ 20) Calculate for the reaction 2 Al (s) + 3 Cl2 (g) 2 AlCl3 (s) from the data. 2 Al (s) + 6 HCl (aq) 2 AlCl3 (aq) + 3 H2 (g) H = -1049. kJ HCl (g) HCl (aq) H = -74.8 kJ H2 (g) + Cl2 (g) 2 HCl (g) H = -1845. kJ AlCl3 (s) AlCl3 (aq) H = -323. kJ 21) Calculate H for the reaction CH4 (g) + NH3 (g) HCN (g) + 3 H2 (g), given: N2 (g) + 3 H2 (g) 2 NH3 (g) H = -91.8 kJ C (s) + 2 H2 (g) CH4 (g) H = -74.9 kJ H2 (g) + 2 C (s) + N2 (g) 2 HCN (g) H = +270.3 kJ 22) Calculate H for the reaction: C2H4 (g) + H2 (g) C2H6 (g), from the following data. C2H4 (g) + 3 O2 (g) 2 CO2 (g) + 2 H2O (l) H = -1411. kJ C2H6 (g) + 3½ O2 (g) 2 CO2 (g) + 3 H2O (l) H = -1560. kJ H2 (g) + ½ O2 (g) H2O (l) H = -285.8 kJ 23) One reaction involved in the conversion of iron ore to the metal is FeO (s) CO (g) Fe (s) CO2 (g) Calculate the standard enthalpy change for this reaction from these reactions of iron oxides with CO : (1) 3 Fe2O3 (s) CO (g) 2 Fe3O4 (s) CO2 (g) H - 47.0 kJ (2) Fe2O3 (s) 3 CO (g) 2 Fe (s) 3 CO2 (g) H - 25.0 kJ (3) Fe3O4 (s) CO (g) 3 FeO (s) CO2 (g) H 19.0 kJ (this one can be tricky if you don’t pay close attention) o 24) Calculate the standard enthalpy change, ΔH , for the formation of strontium carbonate (the material that gives the red color in fireworks) from its elements. Sr (s) C(graphite) 3 O2 (g) SrCO3 (s) 2 The information available is (1) Sr (s) 1 2 O2 (g) SrO (s) H - 592 kJ (2) SrO (s) CO2 (g) SrCO3 (s) H - 234 kJ (3) C(graphite) O2 (g) CO2 (g) H - 394 kJ a. Is this reaction endothermic or exothermic? b. Would the reverse reaction be endothermic or exothermic? c. Does this make sense? The forward reaction is the formation of the firework chemical SrCO3 while the reverse reaction would be the same reaction that occurs when you light the firework.
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