7.2 Temperature and the Phases of Matter Vocabulary Fahrenheit scale Celsius scale thermometer solid liquid gas Intermolecular forces evaporation absolute zero Kelvin plasma

Objectives Convert between temperature scales. Explain the relationship between temperature and the movement of particles in a system. Describe the relationship between temperature and states of matter.

Measuring Temperature Fahrenheit freezes at 32 degrees boils at 212 degrees Celsius freezes at 0°C boils at 100°C.

Comparison of Fahrenheit and Celsius

Converting Between the Scales

Thermometer an instrument that measures temperature

Temperature and Energy Temperature is a measure of the kinetic energy. Atoms in a solid material act like they are connected by springs

Average Motion Is the motion of the whole collection or all the atoms together. The kinetic energy that comes from the average motion of all the atoms together is not what temperature measures.

Random Motion Each atom in an object jiggles back and forth independently of the other atoms.

Temperature and Random Motion Temperature measures the kinetic energy in just the random motion. Temperature is not affected by any kinetic energy associated with average motion.

Melting and Boiling Even rocks can melt and boil if they have enough heat applied to them. The higher the temperature, the higher the random kinetic energy of each atom.

The Phases of Matter Solid holds its shape. Liquid holds its volume, — it flows. Gas flows like a liquid, but can also expand or contract to fill a container gas does not hold its volume

Plasma: A Fourth State of Matter Temperatures greater than 10,000 °C the atoms in a gas start to break apart. In the plasma state, matter becomes ionized. Plasma can conduct electricity. Ex: Lightning, the sun, nebulas

Intermolecular Forces The force that attracts molecules together when they are close. Different strength Their strength determine if matter exist as solid, liquid or gas.

Temperature vs. Intermolecular Forces Kinetic energy from temperature tends to push molecules apart. If temperature wins you have gas. Intermolecular forces tend to bring molecules together. If intermolecular forces win you have a solid.

Strength of Intermolecular Forces Iron is a solid at room temperature and water is a liquid at room temperature. Which has a stronger intermolecular force? Why?

Changing Phase The melting point is the temperature at which a substance changes from a solid to a liquid. Different substances have different melting points. Different particles have different intermolecular strength.

Changing Phase Boiling takes place within the liquid as bubbles of gas particles form and rise to the surface. Intermolecular forces are completely pulled apart.

Changes in State Require Energy It takes energy to break the bonds created by intermolecular forces.

Absolute Zero Molecules have the lowest energy they can have. Absolute zero occurs at minus 273°C (-459°F) You cannot have a temperature lower than absolute zero.

The Kelvin Scale Useful for many scientific calculations. Starts at absolute zero. Measures the actual energy of atoms.

Converting to Kelvin Example: Kelvin (K) unit of temperature is the same size as the Celsius unit Add 273 to the temperature in Celsius to get the temperature in Kelvins. Example: 21°C is equal to 294 K (21 + 273).

7.2 Section Review Page 175 A comfortable room temperature is 20ºC. What is this temperature in degrees Fahrenheit? In which system are the molecules moving faster, a cold glass of tea or a hot cup of tea? Describe what happens at the atomic level during melting. Explain why particles in a gas are free to move far away from each other.