When 1.75 g of acetone, C_3H_6O, vaporizes at 298 K, 933 J of heal is absorbed.

Question

When 1.75 g of acetone, C_3H_6O, vaporizes at 298 K, 933 J of heal is absorbed. Calculate the enthalpy of vaporization, Delta H_vap (in kJ/mol), of acetone at 298 K. Calculate the total amount of heat (in kJ) absorbed when 45.4 g of ice, initially at -20.0 degree C, is completely converted into steam at 120.0 degree C? (Specific heat (J/g. degree C): ice and steam = 2.0; water = 4.184; Delta H_fus = 6.02 kJ/mol; delta H_vap = 40.6 kJ/mol) A sample of ice at 0.0 degree C is added to 100.0 g of water at 35.0 degree C. The final temperature of mixture is 18.5 degree C. Calculate the mass of ice. (Specific heat (J/g. degree C) of water - 4.184; Delta H_fus = 6.02 kJ/mol); The enthalpy of vaporization of Freon (CCl_2F_2) is 167 kJ/kg at its boiling point (-29.8 degree C, 1 atm) If the enthalpy of fusion of water at 0 degree is 6.02 KJ/mol. how many grams of Freon must evaporate to freeze 45.4 g of water at 0 degree C?

Explanation / Answer

4)

1st calculate the heat required to freeze the water

mol of water = mass of water / molar mass of water

= 45.4 g / 18 g/mol

= 2.52 mol

heat required,

Q = n*Hfusion

= 2.52 mol * 6.02 KJ/mol

= 15.2 KJ

This heat must be supplied by Freon

Heat supplied by Freon, Q = 15.2 KJ

use:

Q = m(freon)*HVap

15.2 KJ = m(freon) * 167 KJ/Kg

m(freon) = 0.0909 Kg = 90.9 g

Answer: 90.9 g

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