Zinc is often used to calibrate calorimeters because it undergoes a very sharp phase transition from the solid to the liquid at 419.5oC. Calculate the enthalpy change when 5 g of zinc metal is heated from 100oC to the point where the entire sample is melted. (The heat of fusion for zinc is 112.4 J/g and its specific heat capacity is 0.388 J/goC.)

I worked this for someone last night. Let me try to find it and I'll post it here.

http://www.jiskha.com/display.cgi?id=1288931370

To calculate the enthalpy change when 5 g of zinc metal is heated from 100°C to the point where the entire sample is melted, we need to consider the energy required to raise the temperature to the melting point, as well as the energy required for the phase transition from solid to liquid.

First, let's calculate the energy required to raise the temperature of the zinc from 100°C to its melting point (419.5°C). We can use the specific heat capacity equation:

q = m × c × ΔT

where:
q is the energy (enthalpy change) in Joules,
m is the mass of the substance in grams,
c is the specific heat capacity in J/g°C, and
ΔT is the change in temperature in °C.

For this calculation:

m = 5 g (given)
c = 0.388 J/g°C (given)
ΔT = (419.5°C - 100°C) = 319.5°C

Now, plug in the values to calculate the energy:

q = 5 g × 0.388 J/g°C × 319.5°C = 622.38 J

So, the energy required to raise the temperature of 5 g of zinc from 100°C to its melting point is 622.38 J.

Next, let's calculate the energy required for the phase transition from solid to liquid. This can be done using the heat of fusion equation:

q = m × ΔH

where:
q is the energy (enthalpy change) in Joules,
m is the mass of the substance in grams, and
ΔH is the heat of fusion in J/g.

For this calculation:

m = 5 g (given)
ΔH = 112.4 J/g (given)

Now, plug in the values to calculate the energy:

q = 5 g × 112.4 J/g = 562 J

So, the energy required for the phase transition from solid to liquid for 5 g of zinc is 562 J.

Finally, to calculate the total enthalpy change, we add the energy required to raise the temperature to the melting point and the energy required for the phase transition:

Total enthalpy change = Energy to raise temperature + Energy for phase transition
Total enthalpy change = 622.38 J + 562 J = 1184.38 J

Therefore, the enthalpy change when 5 g of zinc metal is heated from 100°C to the point where the entire sample is melted is 1184.38 J.