Question

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Postlab questions 1. An unknown metal sample weighing 9.25 grams is heated to 97.8°C in a hot water bath to establish thermal equilibrium. The hot metal sample is quickly transferred to 50.0 grams of water at 24. 5C contained in a Styrofoam "Coffee Cup" calorimeter. Thermal equilibrium temperature of the unknown metal and water mixture is 27.4'c. What is the specific heat of this unknown metal? 2. The final temperature of a mixture of solution prepared by dissolving 2.50 grams of NaOH in 750 ml, of water (both initially at 25°C) increases to 25.5 "C. Is this process exothermic or endothermic? What is the enthalpy of solution of NaOH in kJ/mole?

Answer 1

Given it unknown metal sample neeighing = 9.25 gram Heated to = 97.8°C Hot metal sample quickly transferred to 50.0 gram of Water at 24.5°C. Equilibrium Temperature = 27.4°C we know; specific heat of unknown metal= 4.2 JIGOL we know, heat transferred - mso let Specitic Heat of unknown metal be smetal. flowchart 97.8°C (metal) ms metal 40, (metal twater eam, 27.4°C m2 Suore 402 water 24.5°C water I heat loss = Heat Gain At eam. Heat gain by water - m2 Swalter CO2 - 50.03 X 4.2 x 27-4-24.5) - 50.0x 4.2 X 2.9 = 609 J Heat loss by metal = heat gain by water 9.25 x Smetal X ( 97-8 - 27.4) 609 smetal = 0.9471gºel specific heat of this unknown metal = 0.945/9°C

+2.50g nown Initial Temp = 25°c 75ml of water Final Temp. of solution = 25.5°C As Temp. Increases; Mence; heat is retcased an end to the system. . The process is ndodhereix. Erothermic we know Swater = 4.2519°C 25.5°C Heat gained a 25°c density of water. Iglme Hence; mass of water = 75 g. heat gained = msno - 75X 4.2 (25-5-257 275X4.28 0.5 = 151.55 on adding 250 g of Nash Heat added = 151.55 Hence; on adding one mole of noun Heat Added = 157.5 x 40 2.50 * 2520J = 2.52 KJ Enthalpy 4 of s of solution of NooH = 2.52465/mole Enthalpy = 185 -2.52 Kilmole
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iven metal sample ntighing 9.25 gpam Heated to 97-°C unknown 17 Hot metal sample quickly transfored to 50.0 Waler at 24.5'C . Equilibrium Tempurature 21.4 c we know; spedbic teat ob wnknown metal 4.2 T1 we lnow Heat tansfoned let Smetai Specitic Heat ot uukn met4 he Fiooch ant 97-8L (Metal) A0 msmetal (metal twater eam) 27.4° 402 water water 24.5°C At eam Meat loss Heat Gain Heat gain bywata m2 Swalor 482 50.0 X4. 2 Yy( 274-24.r) 50-0X 4.2 X 2-9 609 J waler eat loss by melat = Heat gain b 9.25 x Smeta X (97-8-27-4) 609 0.94 T1 Smetal this unknoun metat 0.94 Tl ot Specilic Heat

27 Nasn Tanitial Temp 25°C 75ml otwato Final Temp. ub solution 25-5°C As Temp. Intneases Mence; neat is added to the sysm . he process is EndothenrmiC enoo Swath f.21c we 25-50 C Heat ned 25°L density ot watn 1glMI Honce; mass ob waler 75 Heat gatned msAe 15x 4.2(25-5-2) 2 75X4.2X0-5 157.5J nt Nas Heat added 157.5T on adding 25D 1 one mole of Nao ading Heat Added 157-5 X40 Hence; 6n 2.5D 2520 J 2-52KJ Enthalpy of solu lien of Noot- 2-52KT/Mol