Cornell Notes 5.1 Temperature and the States of Matter Pages 137 & 139 January 24, 2012

Temperature Temperature is the measurement we use to make the sensations of hot and cold more precise. A thermometer is an instrument used to accurately measure temperature. Temperature is really the average level of heat!

Heat and thermal energy Temperature measures a kind of energy called thermal energy. Thermal energy comes from the motion of atoms in matter. We call thermal energy that is flowing heat.

Heat and thermal energy Thermal energy is often measured in calories. One calorie is the amount of energy it takes to raise the temperature of one milliliter of water by one degree Celsius.

Calories and Food The calories you see on food labels are actually Kilocalories (1000 calories.) One food calorie is the amount of heat it takes to raise 1 kg of water by 1˚C

Extreme Temperatures 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” – it is the point at which they stop moving

Liquids and Gases A fluid is a form of matter that flows when any force is applied. Gases and liquids are both called fluids.

Liquids and Gases In a liquid, molecules can slide over and around each other. This is why liquids flow and can change shape.

Liquids and Gases A gas is a phase of matter with high energy molecules that can expand to fill a container. Molecules in a gas are free to move around and so gases flow just like liquids. Molecules in a gas have much more energy than molecules in a liquid.

Difference Between Liquids and Gases The difference between a liquid and a gas is that a liquid has a fixed volume (it takes up the same amount of space) while a gas has the volume of its container (it spreads through the room.)

Solid Matter In a solid, thermal energy keeps the molecules moving, but because of those intermolecular forces, they only “spring” back and forth around the same average position. This is why solid materials hold their shape and have constant volume.

The molecules of solids shake in place. The molecules of liquids slide around each other, but stay attached. The molecules of gases fly everywhere they can. Gas molecules move fastest, liquid molecules are slower, and solid molecules move the slowest.

There are two types of forces that act between atoms. Bonds in Matter There are two types of forces that act between atoms. Molecular bonds holds atoms together in molecules. They are hard to break. Intermolecular forces hold the molecules together in substances – they are weaker.

Intermolecular Forces Na Cl Na Cl Molecular Bonds Intermolecular Forces Na Cl Na Cl

Intermolecular Forces The phases of matter (solid, liquid, gas) exist because of competition between thermal energy and intermolecular forces. When molecules have a large amount of thermal energy (high temperatures), intermolecular forces are overcome and the molecules spread apart, as in a gas.

Intermolecular Forces When molecules have a medium amount of thermal energy, they come together to form a liquid because the intermolecular forces are partially overcome.

Intermolecular Forces When molecules have a small amount of thermal energy, the intermolecular forces are stronger and molecules become fixed in place as a solid.