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Chrome File Edit View History Bookmarks People Window Help Student x ) D CALM: Computer Assisted Lea D FlinnPREP courses C secure https://calmweb.chem.indiana.edu/FtworthCountryDayTXHS5/cgi-bin/bmw.pl?sid.151 alm 369962622 Tutorial Trouble Report Message Board Professor To Exit Topic 5-Thermodynamics Section 1-Thermochemistry Question 13 Sodium metal reacts violently with water to produce hydrogen gas and sodium hydroxide 2 Na(s) + 2 H2O(l) 2 NaOH(aq) + H2(g) A student adds 0.76 grams of Na metal 1 to 250 mL of water and the temperature changes from 255°C to 34.4 oC. Calculte hn in units of kJ/mol. What is the alHpun? Push mel to continue. kJ/mol. Department of Chemistry I College of Arts and Sciences I Chemistry Library 1 OoeStart Personnel 1 CALMIC 800 E. Kirkwood Ave., Bloconingio. IN 47405-7102 1 Ph: (812) 8SS9043ih:(812) 8ssoo · Copyright O2008 I The Trustees ef Indiana University I Copyright Complaints

Explanation / Answer

Q = mcT

Q = heat energy (Joules, J)

m = mass of a substance (g), here water, 250 g

c = specific heat (units J/g °C), 4.184 J/g °C (specific heat of water)

T = change in temperature (Celsius, C), (34.4 - 25.5) = 8.9 °C

Q = mcT

so, Q = 250 g x 4.184 J/g °C x 8.9 °C = 9309.4 J = 9.31 kJ

so 0.76g of sodium metal gives 9.31 kJ of heat, so one mole of sodium (23 g) will corresopnd to

(9.31 x 23)/ 0.76 = 281.75 kJ/mol

so Hrxn is 281.75 kJ/mol

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