calculate the enthalpy change of 50.0g of water from 10 degrees celcius to 150 d

Question

calculate the enthalpy change of 50.0g of water from 10 degrees celcius to 150 degrees Celsius? The specific heat of water is 4.18 J/g K and that of steam is 1.84 J/g K. The heat of vaporization is 40.67 kJ/ mol. calculate the enthalpy change of 50.0g of water from 10 degrees celcius to 150 degrees Celsius? The specific heat of water is 4.18 J/g K and that of steam is 1.84 J/g K. The heat of vaporization is 40.67 kJ/ mol. calculate the enthalpy change of 50.0g of water from 10 degrees celcius to 150 degrees Celsius? The specific heat of water is 4.18 J/g K and that of steam is 1.84 J/g K. The heat of vaporization is 40.67 kJ/ mol.

Explanation / Answer

this process takes place in three steps

1) first the temp of wate is raised from 10 C to 100 C

2) at 100 C the water is vaporized

3) then the temp of steam is raised from 100 C to 150 C

now conisder the first step :

water is raised from 10 C to 100 C

we know that

heat = mass x specific heat x temp change

given

50 g of water

temp change = 100-10 = 90

so

heat = mw x sw x dT

Q1 = 50 x 4.18 x 90

Q1 = 18810 J

Q1 = 18.81 kJ

now consider the second step :

we know that

moles = mass / molar mass

so

moles of water = 50 / 18

moles of water = 2.778

all the water is vaporized

we know that

during vaporization

heat = moles x latent heat of vaporization per mole

so

Q2 = 2.778 x 40.67

Q2 = 112.97 kJ

consider the third step :

steam is raised from 100 C to 150 C

heat = mass x specific heat x temp change

so

Q3 = 50 x 1.84 x (150-100)

Q3 = 50 x 1.84 x 50

Q3 = 4600 J

Q3 = 4.6 kJ

finally

enthalpy change = Q1 + Q2 + Q3

enthalpy change = 18.81 + 112.97 + 4.6

enthalpy change = 136.38 kJ

so the enthalpy change is 136.38 kJ   

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