of the chemical substances they can react to form, namely, lead sulfate and water. When fully charged, the voltage between the terminals of a lead storage battery is 2.0 volts. Most automobile starters require either 6 or 12 volts to function, so the car batteries consists of 3 or 6 individual lead cells connected together to provide the proper voltage. By connecting the terminals of the battery to a source of direct current which, flows in the direction opposite to that of normal battery current flow, the battery can be recharged. Phase Change - The term phase as used here relates to the fact that matter exists either as a solid, liquid, or gas such as ice, water, and steam for H 2 O. Transitions from one phase to another are accompanied by the absorption or liberation of heat and usually by a change in volume. Figure 12-24 uses H 2 O as an example to illustrate the process of phase change. The experiment puts ice (at -25 o C) into a container, which is surrounded by a heating coil (generating an uniform heating rate). Temperature of the ice rises from a to b until it reaches 0 o C - the melting point. Ice turns into water from b to c. The heat spent for the phase change (per unit mass) is called the heat of fusion. The temperature remains constant during the change of phase. Once the conversion is complete, the temperature of the water starts to rise