As Figure above shows, the distance between particles is much smaller for the solid and liquid states than for the gas state. In the solid state, particles are fixed in place, while particles are more free to move in the liquid and gas states. The particles in the solid and liquid states “stick together,” but in the gas state, they move freely about the container. In general, it requires energy to separate individual particles. If we want to make a solid adopt a liquid form, we can add energy in the form of heat, increasing the temperature of the substance. Conversely, if we want to convert a substance from a gas to a liquid or from a liquid to a solid, we remove energy from the system and decrease the temperature. Pressure also plays an important role in changes of state, which will be discussed later on. We will study these difference in greater detail in the chapter States of Matter.
Jane loved making chocolate candies for Christmas to give to all her friends. First she got her double boiler out and added water before placing it over a flame. When she noticed steam coming up from the pan Jane placed solid chunks of chocolate into the pan and gently stirred until the chocolate was melted. She then added dried fruit and nuts to the chocolate. After scooping spoonfuls onto a pan she placed the pan into the freezer to cool. 20 minutes later her candies were ready to box up for gifts.
When the chocolate was solid were the particles fixed or free to move around?