Name ______

THERMODYNAMICS

Introduction - Water exists in all 3 phases of matter, which are (s)______, (l)__water____, and (g) ______. It requires heat energy to change the phase of water from solid to liquid and from a liquid to a gas, meaning heat needs to be absorbed. When water vapor changes into liquid water, energy is (released or absorbed). Therefore, when condensation occurs in the atmosphere energy is (added or taken away) from the atmosphere.

The strange thing about water is that when a phase change occurs, the temperature of the water does not change. As water boils when you’re making pasta, the temperature of the water remains at 100° C. The heat energy that is added while a phase change occurs is called Latent Heat, which is a form of Potential Energy. It is potential energy because now the water vapor has the potential to release energy when condensation occurs.

Vocabulary:

Freeze –

Condensation –

Evaporation –

Melt –

Joules –

Latent Heat -

Heat of Vaporization

Heat of Fusion -

An experiment was performed in a laboratory under ideal conditions. Heat energy was added to one gram of ice at -100°C until it was water vapor at 200°C. The number of joules of heat added and the temperature of the subject was recorded in the table below.

Procedure - Plot the data below on the graph on the following page. After you are finished, connect the points. Label the parts of your graph were the following take place: melting, condensation, evaporation, and freezing. Then answer the questions that follow.

Temp (°C) / Heat (Joules) / Temp (°C) / Heat (Joules) / Temp (°C) / Heat (Joules)
-100 / 0 / 10 / 586 / 100 / 2092
-75 / 52 / 25 / 649 / 100 / 2510
-50 / 105 / 50 / 753 / 100 / 2929
-25 / 159 / 75 / 858 / 100 / 3222
0 / 209 / 100 / 962 / 125 / 3272
0 / 334 / 100 / 1046 / 150 / 3322
0 / 418 / 100 / 1255 / 175 / 3372
0 / 544 / 100 / 1674 / 200 / 3422

Questions:

1.How many joules were required to change the gram of ice at 0°C to water at 0°C? (hint look at the chart, take the joules at the last 0°C reading and subtract from the joules at the first 0°C)?

2.How many joules were required to change the gram of water to a gram of water vapor (steam)?

3.Which process requires more energy, melting a gram of ice or evaporating a gram of water? How does the length of your flat lines compare for each?

4.How did the temperature change as the ice was melting?

5.How did the temperature change as the water was boiling?

6.How does the distance between molecules change as an object is heated from a solid to a gas?

7.When energy is being absorbed during a phase change latent heat is created, during which phase changes is latent heat created, or put into storage? During which phase changes is latent heat released?

8.For the following write down if energy is released or absorbed, and also how many joules are released or absorbed.

Liquid to Gas ______Liquid to Solid ______

Solid to Liquid ______Gas to Liquid ______

Conclusion - Describe how kinetic and potential energy change as water is heated from ice to steam.

Heat Energy (Joules)

Heat Energy (Joules)