Matter

Chapter Eleven: Temperature, Heat and the Phases of Matter 11.1 Temperature and the Phases of Matter 11.2 Heat

Investigation 11A Temperature and Heat How are temperature and heat related?

11.1 Temperature There are two common temperature scales. On the Fahrenheit scale, water freezes at 32 degrees and boils at 212 degrees. The Celsius scale divides the interval between the freezing and boiling points of water into 100 degrees.

11.1 Thermometer A thermometer is an instrument that measure temperature. A type of thermometer you have likely seen uses colored liquid alcohol to sense temperature.

11.1 What temperature really is Atoms are in constant motion, even in a solid object. The back-and-forth jiggling of atoms is caused by thermal energy, which is a kind of kinetic energy.

11.1 What temperature really is Temperature measures the kinetic energy per atom due to random motion. A moving rock has both a velocity and a temperature.

11.1 Absolute zero Absolute zero is -273°C. You cannot have a temperature lower than absolute zero. Think of absolute zero as the temperature at which atoms are “frozen.”

11.1 Converting to Kelvin The Kelvin temperature scale is useful in science because it starts at absolute zero. To convert from Celsius to Kelvin, you add 273 to the temperature in Celsius.

11.1 The phases of matter A solid holds its shape and does not flow. The molecules in a solid vibrate in place, but on average, don’t move far from their places.

11.1 The phases of matter A liquid holds its volume, but does not hold its shape—it flows. Liquids flow because the molecules can move around.

11.1 The phases of matter A gas flows like a liquid, but can also expand or contract to fill a container. A gas does not hold its volume. The molecules in a gas have enough energy to completely break away from each other.

11.1 The phases of matter Within all matter, there is a constant competition between temperature and intermolecular forces. Intermolecular forces tend to bring molecules together.

11.1 The phases of matter The forces in chemical bonds are stronger than intermolecular forces.

11.1 Melting and boiling The melting point is the temperature at which a substance changes from a solid to a liquid.

11.1 Melting and boiling The temperature at which a liquid becomes a gas is called the boiling point.

As heat energy is added to ice, the temperature increases until it reaches 0°C. Then the temperature stops increasing. As you add more heat, more ice becomes liquid water but the temperature stays the same. This is because the added energy is being used to break the intermolecular forces and change solid into liquid. Once all the ice has become liquid, the temperature starts to rise again if more energy is added.

11.1 Melting and boiling points of common substances Materials have a wide range of melting and boiling points.

11.1 Melting and boiling points of common substances Most materials have a higher density as a solid than as a liquid. Water is an exception. Ice wouldn’t float if ice were more dense than water! Ice helps fish and other aquatic organisms to survive over long, cold winters because the protective layer keeps the water below it warmer.