# Homework Help: Turn water to steam

1. Jul 1, 2007

### mike2007

How much heat must be added to 120g of water at an initial temperature of 60C to
heat it to the boiling point?
completely convert the 100C water to steam?

Specific heat capacity of water = 1.0cal/g-C
It would take 120*1 to raise 120g of water up to 1C
difference in temperature = 100C - 60C = 40C
It would then take 120*40 to raise it to the boiling point
120*40 = 4800cal

specific heat of steam is 0.48 cal/g-C but what it the temperature of steam?

2. Jul 1, 2007

### Astronuc

Staff Emeritus
Temperature of steam at 1 atm (0.101325 MPa, or 14.7 psia) is 100°C (212°F). Steam represents a phase change.

Steam however can be superheated, but that would be in a vessel with higher steam pressure, otherwise the steam expands and cools.

Remember, the problem increasing the water temperature, then transforming liquid water at 100°C to steam (water vapor) at 100°C.

See
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/phase2.html#c3
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/phase.html

Last edited: Jul 1, 2007
3. Jul 1, 2007

### mike2007

But what do i use for the calculation of water to steam. Doesnt the system have to have some amount of heat added to convert it to steam.

4. Jul 1, 2007

### Feynman diagram

You need the latent heat of vapourization of water for the last part of the calculation, not the specific heat of steam ;)

5. Jul 1, 2007

### Astronuc

Staff Emeritus
Look at the first link I provided.

Converting liquid water to steam at 100°C (0.101325 MPa) requires a heat addition of 539 cal/g (2260 J/gm).

6. Jul 1, 2007

### mike2007

The latent heat for boiling is 540 cal/g. That means that 1g requires 540 cal of heat to steam

Thus, 120g requires 120 x 540 = 64800 cal to steam

7. Jul 1, 2007

### Astronuc

Staff Emeritus
Correct.

And then add the two heat requirements.