A sample of a solid substance has a mass of 0.520 kg. Starting from 20 deg C, it

Question

A sample of a solid substance has a mass of 0.520 kg. Starting from 20 deg C, it is gently heated to 400 degrees as shown in the graph below.

Heating_graph (The horizontal axis inidicates minutes. Each minute shown corresponds to 45000 Joules of heating.)

Table fill in:

Melting temperature:_________ degrees.

Boiling temperature:_____________ degrees.

specific heat of liquid phase: ______________J/kg deg.

specific heat of vapor phase: ____________________J/kg deg.

latent heat of fusion/melting: ___________________J/kg .

latent heat of vaporization:____________________ J/kg .

Explanation / Answer

Before proceeding to answer this question, let us look at the stages of heating of a substance. basically while heating a solid substance, there are two scenarios possible. 1. While heating, temperature increases and the phase remains same 2. temperature does not increase but with the addition of heat the phase changes i.e. solid gets converted into liquid and then liquid gets converted to gas and so on.

In the above graph, temperature remains constant at 200 C and at 300 C.

so, melting temperature = 200 C

boiling temperature = 300 C

Now to calculate the specific heat, we need to find the heat supplied. As minute axis is not clear, let us assume that time required for liquid phase = 8 minute ( i.e. time taken from 200 C to 300 C)

As 1 minute corresponds to 45000 j of heating, so total heat supplied during liquid phase heating = 45000 x 8 = 360000 J

As we know, heat supplied = mass x specific heat x temperature difference

so, 360000 = 0.520 x specific heat x (300-200)

so, specific heat during liquid phase = 6923.07 J/kg

similarly, for finding the specific heat during vapor phase, we need to calculate the heat supplied.

Time taken = 2 min (i.e. time taken from 300 C to 400 C)

heat supplied = 45000 x 2= 90000 J ( As 1 minute corresponds to 45000 j of heating)

As we know, heat supplied = mass x specific heat x temperature difference

so, 90000 = 0.520 x specific heat x (400-300)

so, specific heat during vapor phase = 1730.77 J/kg

latent heat of fusion is the amount of heat required /kg to change the phase from solid to liquid.

In this case the temperature remains constant for 9 minutes at 200 C i.e. the melting process takes 9 minutes.

As 1 minute corresponds to 45000 j of heating, so total heat supplied = 45000 x 9= 405,000 J

For 1 kg, amount of heat required during melting= 405,000/0.52= 778,846.15 j/kg

so latent heat of fusion =778846.15 J/kg

latent heat of vaporisation is the amount of heat required /kg to change the phase from liquid to gas.

In this case the temperature remains constant for 13 minutes at 300 C i.e. the vaporzation process takes 13 minutes.

As 1 minute corresponds to 45000 j of heating, so total heat supplied = 45000 x 13= 585,000 J

For 1 kg, amount of heat required during vaporization= 585,000/0.52= 1125000 j/kg

so latent heat of vaporization =1125000 J/kg

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