cotol-assighment-take Use the References to access important values if needed fo
ID: 692220 • Letter: C
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cotol-assighment-take Use the References to access important values if needed for this question. The following information is given for magnesium at 1atm: Th = 1090.00°C Tu = 649.00°C Specific heat solid = 1.017 J g °C Specific heat liquid 1.339 J g (1090.00)-5.424 x 10 Jg A H fh (649.00c)-368.3Jg A 22.90 g sample of liquid magnesium at 704.00°C is poured into a mold and allowed to cool to 25.00°C. How many kJ of energy are released in this process? Report the answer as a positive number.) Energy = kJ Retry Entire Group No more group attempts remain Submit AnswerExplanation / Answer
When we cool magnesium in mold from 704.0 oC to 25.0 oC until it becomes solid at 25.0 °C, we are proceeding through 3 steps, and you have to make the calculations for each of those steps.
q = c · m · T { where q = heat, c = specific heat cont. m = mass,T = temperature diferece }
Heat of fusion of magnesium : Hf = 368.3 J/g
Heat of vaporization of magnesium : Hv = 5424 J/g
Specific heat of solid magnesium : c = 1.017 J/gC;
Specific heat of liquid magnesium : c = 1.339 J/gC
step 1)
Find the heat released from liquid magnesium cooling to the temperature by 55.0 °C from 704.0 °C to 649.0 °C.
q1 = m .cliquid Mg T1
q1 = (22.9 g) (1.339 JgC) ( 55 ) C
q1 = 1686.4705 J
step 2)
Find the latent heat released to freez Mg liquid at 649.0 °C into solid Mg at 649.0 °C.
q2 = m Hf
q2 = (22.9 g) (368.3 J/g)
q2 = 8434.07 J
step 3)
Find the sensible heat released to decrease the temperature of Mg solid by 624.0 °C from 649.0 °C to 25.0 °C.
q3 = m c T3
q3 = (22.9 g) (1.017 JgC) (624 )C
q3 = 14532.5232 J
total amount of energy released to mold from Mg liquid at 704.0 C to solid Mg at 25.0 C will be the sum of all the calculated energies
qtotal = q1+ q2 + q3
qtotal = 24653.0637 J
qtotal = ~ 24.65 KJ
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