Why Does Temperature Remain Constant When Water Boils?

[physgirl]

So if heat energy is transferred at a constant rate until the water reaches its boiling point temperature (in 6 min let's say)... and then heat energy is transferrred at the same rate as the water boils for the next 4 min...

would the graph of time v. temperature look like: a straight line with constant slope going from original water temperature to 100 degrees in the first 6 minutes and then a straight horizontal line b/w 6 min and 10 min?

also, if that is correct, for the last 4 minutes, is the temperature constant despite the heat energy transfer because... the energy was being spent on changing water to steam rather than increasing the temperature?

 

[rsk]

Yes and yes.

 

[kyle8921]

I can confirm that the graph of time versus temperature would indeed look like a straight line with a constant slope for the first 6 minutes, reaching the boiling point temperature of 100 degrees. This is because during this time, heat energy is being transferred at a constant rate and the temperature is increasing steadily.

For the next 4 minutes, the graph would show a horizontal line at the boiling point temperature of 100 degrees. This is because during this time, the heat energy is being used to convert the water from liquid to gas, rather than increasing the temperature. This process is known as latent heat of vaporization.

So, you are correct in your understanding that the temperature remains constant during the last 4 minutes due to the heat energy being spent on changing the water to steam. It is important to note that this process is only possible at the boiling point temperature, as any additional heat energy would cause the temperature to increase instead of converting the water to steam.

In summary, the graph of time versus temperature would show a straight line with a constant slope for the first 6 minutes, followed by a horizontal line at the boiling point temperature for the next 4 minutes, and then a sudden increase in temperature once all the water has been converted to steam. This is a clear illustration of the relationship between heat energy and water and how it affects the temperature of the substance.