2003 Virginia SOLs
Motivation for Learning
Matter can undergo a physical change from one state to another: solid, liquid or gas. When a material changes from a solid to a liquid, the process is called melting, and occurs at a temperature called the melting point, which is specific to the given substance. The liquid can change back into a solid by freezing; this same temperature is called the freezing point. When a liquid boils, it vaporizes and becomes a gas; at that temperature, called the boiling point, the gas can also become a liquid. This process is called either condensation (gas to liquid) or vaporization (liquid to gas). Under certain conditions, it is possible for a substance to change from a solid to a gas or vice versa in a process called sublimation.
The particles (atoms or molecules) of a material in each of these three states have different properties. In a solid, they are held together very tightly and have little room to move; in a liquid, the particles have more energy than in a solid and are able to move around more; in a gas, particles are not held together at all and are able to move around completely. They have much more energy and move more quickly than those in the other two states. When the temperature of a solid rises, energy is added and the kinetic energy of its individual particles increase. Eventually, the temperature reaches a point at which the added energy breaks forces between individual particles, allowing for more movement. This is the melting point, and the solid becomes a liquid. The amount of energy necessary to induce this change is called the heat of fusion. A similar process occurs when a liquid becomes a gas, and the required energy is called the heat of vaporization.
In this experiment, the students will study these three phases of water by melting ice and then boiling water. They should record the temperature of the liquid over a period of time and plot this data in order to visualize the two changes of state. At each point, the temperature should stabilize briefly as the heat energy is absorbed and a portion of the graph will be horizontal. From this plot, the students should be able to determine the freezing, melting and boiling points of water.
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Students with Special Needs
All students should be able to participate in this acitivity.
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information on laboratories with students with special needs.
Data sheet to be completed during the laboratory.