Unit 2 Heat and temperature

What is matter? -Matter is what makes up all substances, whether it is a solid, liquid or gas. Molecules, atoms and sub-atomic particles are all matter.

What’s matter made of? -All matter is made up of constantly jiggling atoms or molecules. The motion of these particles determines whether a substance is a solid, liquid, or a

States of Matter Solid Liquid Gas

What are the properties of each state of matter? -Each state of matter has different properties. Solids Have definite shape. Have definite volume In a solid, the particles are so close that the forces of attraction confine the material to create the specific shape. In solids, the motion of the particles is severely constrained to a small area, in order for the solid to maintain its shape.

Liquids Have definite volume. Takes the shape of the container In a liquid, the particles are farther apart, but they are still close enough that attractive forces confine the material to the shape of its container. In liquids, the movement is somewhat constrained by the volume of the liquid

Gases Has no definite shape Has no definite volume In a gas, the separation between particles is very large compared to their size, such that there are no attractive or repulsive forces between the molecules. In gases, the movement of the particles is assumed to be random and free.

How does each state of matter change How does each state of matter change? - Each change in the state of matter has a specific name. Start from: Change to: Name Solid liquid melting Liquid solid freezing gas boiling condensation gas (skipping liquid phase) sublimation solid (skipping liquid phase) deposition

What does this have to do with energy transfer or heat flow? - Collisions of particles transfer energy, in effect creating heat transfer by conduction. Particles often collide with each other, when this happens energy is transferred from the faster (hotter) moving particle to the slower (cooler) moving particle. This makes the slower moving particles increase in speed.

When molecules in a substance are made to move faster, they get warmer When molecules in a substance are made to move faster, they get warmer. The warmer an object gets, the more kinetic energy and thermal energy it contains. Kinetic energy – energy of motion Thermal energy – total energy of the atoms and molecules

What does all of this have to do with temperature? -Temperature is the measurement of the average internal kinetic energy of the material or object. When a material reaches the temperature at which a change in state occurs, the temperature will remain the same until all the energy is used to change the state.

How high can something’s temperature go? -In principle, temperature has no upper limit. However, there is a limit to how cold something can get, it is absolute zero. At this point all particle movement has stopped.

What is heat? What is cold? -Heat is the movement, or transfer of thermal energy. -Cold is the lack of thermal energy. The direction of thermal energy flow is always from warmer to colder. Ex. Hand touches a hot stove – hand gets burned Ex. Hand touches ice – ice starts to melt.

Is all of the heat transferred, or is some destroyed? -It can’t be destroyed; it is transferred without a net loss or net gain. The Law of conservation of energy states that energy can not be created or destroyed, it can only be changed from one form to another.

We apply the above law to thermal systems to get the First law of thermodynamics: -Whenever heat flows into or out of a system, the gain or of loss thermal energy equals the amount of heat transferred.

The Second law of thermodynamics restates what we’ve learned about the direction of heat flow. -Heat never spontaneously flows from a cold substance to a hot substance.

The Third law of thermodynamics deals with absolute zero. -No system can reach absolute zero.

Why do some things stay hot longer than others? -Different substances have different capacities for storing thermal energy. Each substance has its own specific heat capacity. The specific heat capacity of any substance is defined as the quantity of heat required to change the temperature of a unit mass of the substance by 1 degree.

Heat Transfer & Change of Phase Why does a silver spoon in left in very hot soup get hot too? -Thermal energy is transferred from the hot end of the spoon through the entire length, it’s called conduction.

Conduction is the transfer of heat energy by collisions between particles in a substance (especially a solid). Electrons in atoms collide with each other inside the object being heated. Good conductors of heat are metals with loose electrons – silver, copper, iron, etc. Poor conductors are called insulators. These don’t have loose electrons – wool, wood, paper, styrofoam, etc.

Do liquids and gases transfer heat by conduction? -Liquids and gases transfer heat mainly by convection. Convection is the transfer of heat by motion of a fluid, or by currents.

When does heat transfer occur? -Heat Transfer occurs whenever matter changes phases. When energy is added and absorbed, the change of phase will move in the following direction: solid > liquid > gas When energy is released, the change of phase will move in the following direction: gas > liquid > solid

Evaporation occurs at the surface of a liquid. What is evaporation? -Evaporation is the process by which a liquid changes to the gaseous phase. Evaporation occurs at the surface of a liquid. Evaporation is a cooling process. Sublimation occurs when molecules jump from a solid phase directly to a gaseous state. Ex. Think of dry ice.

What’s the opposite of evaporation? -Condensation Condensation is the changing of a gas to a liquid. Condensation is a warming process.

How does boiling relate to evaporation? -Boiling is evaporation within a liquid. Boiling is a cooling process.

What is melting? -Melting occurs when a substance changes from a solid to a liquid. As the kinetic energy increases, the molecules can not stay in the same tight structure of the solid.

What’s the opposite of melting? -Freezing. Freezing occurs when a liquid changes to a solid.

What do you need for a change of phase? -Energy A transfer of energy occurs at every change of phase. Heat of Fusion – the amount of energy needed to change any substance from solid to liquid (or a liquid to solid). Heat of Vaporization – the amount of energy required to change any substance from liquid to gas (or a gas to liquid).