Equations The heat energy associated with a change in temperature that does not

Question

Equations

The heat energy associated with a change in temperature that does not involve a change in phase is given by

q=msT

where q is heat in joules, m is mass in grams, s is specific heat in joules per gram-degree Celsius, J/(gC), and T is the temperature change in degrees Celsius. The heat energy associated with a change in phase at constant temperature is given by

q=mH

where q is heat in joules, m is mass in grams, and H is the enthalpy in joules per gram.

Physical constants

The constants for H2O are shown here:

Specific heat of ice: sice=2.09 J/(gC)

Specific heat of liquid water: swater=4.18 J/(gC)

Enthalpy of fusion (H2O(s)H2O(l)): Hfus=334 J/g

Enthalpy of vaporization (H2O(l)H2O(g)): Hvap=2250 J/g

Part A

How much heat energy, in kilojoules, is required to convert 30.0 g of ice at 18.0 C to water at 25.0 C ?

Express your answer to three significant figures and include the appropriate units.

Part B

How long would it take for 1.50 mol of water at 100.0 C to be converted completely into steam if heat were added at a constant rate of 25.0 J/s ?

Express your answer to three significant figures and include the appropriate units.

Explanation / Answer

ice converted to water at 0C0

q=msT

= 30*2.09*(0-(-18)

= 1128.6J

heat of fussion of ice

q = mass * enthalpy of fussion of ice

     = 30*334 = 10020J

water converted at 0C to 25C0

q=msT

= 30*4.18*(25-0)

= 3135J

total heat = 1128.6 + 10020 +3135 = 14283.6J = 14.2836KJ

part B

mass of water = no of moles * molar mass

                        = 1.5*18 = 27g

heat = mass* entahlpy of vapourisation

       = 27*2250 = 60750J

time = Q/25J/sec

       = 60750J/25J/sec

      = 2430sec = 2.43*103 sec

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