Loudoun County Public Schools / Overview



ANSWERS: Energy, Solids, and Liquids Worksheet1. A 15.75-g piece of iron absorbs 1086.75 joules of heat energy, and its temperature changes from 25°C to 175°C. Calculate the specific heat capacity of iron. Q=mc?T 1086.75 J = (15.75)(c)(150) c = 0.460 J/goC2. How many joules of heat are needed to raise the temperature of 10.0 g of aluminum from 22°C to 55°C, if the specific heat of aluminum is 0.90 J/g°C? Q=mc?T Q = (10.0g)(0.90)(33) Q = 297J3. To what temperature will a 50.0 g piece of glass raise if it absorbs 5275 joules of heat and its specific heat capacity is 0.50 J/g°C? The initial temperature of the glass is 20.0°C. Q=mc?T 5275 J = (50.0)(0.50)(?T) ?T = 211oC Final Temp = 211 + 20.0 = 231oC4. 100.0 mL of 4.0°C water is heated until its temperature is 37°C. If the specific heat of water is 4.18 J/g°C, calculate the amount of heat energy needed to cause this rise in temperature. 100.0 mL = 100.0g Q=mc?T Q = (100.0)(4.184)(33) Q=14,000 J5. What is the specific heat capacity of silver metal in J/goC if 55.00 g of the metal absorbs 47.3 calories of heat and the temperature rises 15.0°C? Q=mc?T 47.4 cal = (55.00)(c)(15) c = 0.05745 cal/goC c = 0.24 J/goC6. A 2.70 gram piece of metal is heated to 98.7 C. It is then added to a beaker containing 150 mL of water at 23.5 C. The final temperature of the water and metal is 25.2 C. What is the specific heat of this metal?Heat Lost = Heat Gained - mc?T metal = mc?T water -(2.70)(c)(-73.5) = (150)(4.184)(1.7) c = 5.4J/goC ___________________________________________________________7.In an exothermic reaction, is the chemical potential energy of the products less or greater than that of the reactants?Products have less potential energy. Energy is released in an exothermic reaction so the products end up with less potential energy.8.In an endothermic reaction, is the chemical potential energy of the products less or greater than that of the reactants?Products have more potential energy. Energy is adsorbed in an endothermic reaction so products end up with more energy stored in them.Classify the following as exothermic or endothermic reactions:550 KJ is released - EXOTHERMICthe metabolism of glucose in the body provides energy - EXOTHERMICThe synthesis of proteins requires energy - ENDOTHERMIC125 KJ is absorbed - ENDOTHERMIC12.Classify the follow as exothermic or endothermic and provide ?H for each reaction: CH4 + 2 O2 ---> CO2 + 2 H2O + 890 kJ EXO ?H = -890 kJ Ca(OH)2 + 65.3 KJ --> CaO + H2O ENDO ?H = +65.3 kJ 2 S + 3O2 ---> 2 SO3 + 790 KJ EXO ?H = - 790 kJ N2 + O2 + 90.2 KJ --> 2 NO ENDO ?H = +90.2kJ13.Old "hot packs" are based on the crystallization of sodium acetate from a highly concentrated solution. What is the sign of ?H for this crystallization? Is the reaction exothermic or endothermic??H is negative Reaction Is exothermic14. Define the molar heat of fusion of a substance?Molar heat of fusion is the heat/energy required to melt a mole of a substance.15.How much energy would it take to melt 36 g of ice at 0oC if the molar heat of fusion of water is 6.02 KJ/mole 36g = 2.0 mole Energy = 2.0 mole x 6.02 kJ/mole = 12 kJ16. Define the molar heat of vaporization of a substance?Molar heat of vaporization is the heat/energy required to convery 1 mole of a substance from the liquid to gaseous phase.17. Rank the following intermolecular forces from the strongest (1) to the weakest (3): _1__ Hydrogen Bonding _3_ London Dispersion Forces __2_ Dipole-Dipole Interactions18.Use your best judgment to rank the following on boiling points from lowest (1) to highest (4): _1_ CH4 _4_ H2O _2__ CH3CH2CH2CH2CH3 _3_ CH2Br219. Define the normal boiling point of a substance?Normal boiling point is the boiling point at 1 atm of pressurePhase Diagram 1For each of the questions on this worksheet, refer to the phase diagram for mysterious compound X.If you have a sample of this compound at 70 atm and 200oC and you raise the temperature to500oC, what will happen (keeping the pressure the same)? _solid will turn to liquid_If you were to have a bottle containing compound X in your closet, what phase would it most likely be in? _GAS_At what temperature and pressure will all three phases coexist? ____around 50 atm and 350oC__ If I have a bottle of compound X at a pressure of 45 atm and temperature of 1000 C, what will happen if I raise the temperature to 4000 C? _____sublimate (go from solid to gas)_________Why can’t compound X be boiled at a temperature of 2000C ____never exists as a liquid at 200oCIf you wanted to, could you drink compound X? NO: it is only a liquid at really high temps and pressures__________9544048364855Solid to liquid around 100oC and then liquid to gas around 200oC0Solid to liquid around 100oC and then liquid to gas around 200oC53352707145655Around 800oC0Around 800oC30683206383655Liquid to gas0Liquid to gas50209455440680N/A0N/A47447205116830Around 400oC0Around 400oC49358544716780Around 100oC0Around 100oC218440482155526.27.28.29.30.31.02000026.27.28.29.30.31.?What is happening to the average kinetic energy of the molecules in the sample during section 1?The average kinetic energy is increasingWhat is the name of the process happening during section (4)? Boiling or VaporizationWhat would be the name of the process happening during section (4) if time were going the other way? CondensingWhat is the melting point of this substance?0oCAt what temperature would this sample boil? 100oCWhen this substance is melting, the temperature of the ice-water mixture remains constant because:Heat is not being absorbedThe ice is colder that the water630555154305Heat energy is being converted to potential energyHeat energy is being converted to kinetic energy7829543695700When a given quantity of water is heated at a constant rate, the phase change from liquid to gas takes longer than the phase change from solid to liquid becauseThe heat of vaporization is greater than the heat of fusionThe heat of fusion is greater than the heat of vaporizationThe average kinetic energy of the molecules is greater in steam than in waterIce absorbs energy more rapidly than water does3352803752850The temperature at which a substance in the liquid state freezes is the same as the temperature at which the substance a.???? Meltsb.???? Sublimesc.???? Boilsd.???? CondensesRead the vapor pressure diagram above.What is the boiling point of ethanol at normal atmospheric pressure (1 atm). Remember, 1 atm = 101.3 kPaAround 80oCWhat is the boiling point of chloroform at 1 atm?Around 60oCIn a closed container, what is the approximate vapor pressure of water at 80oC? 50 kPa ................
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