Matter Intermolecular Forces  Are the forces between neighboring molecules

Physical State of Matter State of matter at room temperature depends on strength of intermolecular forces ( IM) For example, a substance with strong IM forces will be a solid while a substance with very weak IM forces will be a gas

Changes of State Energy and change of state… To change states, particles must overcome the attractive forces holding them together (the number of particles does not change)

Changes of State Vaporization Liquid changes to a gas, also called evaporation, requires energy input

Changes of State Vaporization Rapidly moving particle near surface of liquid gains enough energy to escape attractive forces of other particles

Changes of State Vaporization Volatile liquid – one that readily evaporates Has weak intermolecular forces

Breaking intermolecular forces. Vaporization - the change from a liquid to a gas below its boiling point. Evaporation - vaporization of an uncontained liquid ( no lid on the bottle ).

Evaporation Molecules at the surface break away and become gas. Only those with enough KE escape Evaporation is a cooling process. It requires energy. It absorbs heat

Condensation /Change from gas to liquid /Molecules stick together /Releases energy.

Changes of State Boiling point Temperature at which vapor pressure becomes equal to the atmospheric pressure

Boiling Making bubbles of gas Forces liquid level to rise Must push against air pressure on the liquid.

Boiling Normal Boiling point is the temperature a substance boils at 1 atm pressure. – The normal boiling point of water is 100 o C The temperature of a liquid can never rise above it’s boiling point Energy goes into breaking forces, not moving faster.

Changing the Boiling Point Lower the pressure (going up into the mountains). Easier to make bubbles means lower boiling point. Food cooks slower.

Changing the Boiling Point Raise the external pressure (Use a pressure cooker) Raises the vapor pressure needed. Harder to make bubbles Raises the boiling point. Food cooks faster.

Changes of State Freezing (Solidification)Solidification Particles get closer together and more organized than in the liquid state, releases energy

Changes of State Melting Particles become less organized and farther apart, requires energy input

Changes of State Sublimation Solid changes directly to a gas, requires energy input

Changes of State Deposition Gas changes directly to a solid, releases energy

Phase Changes Solid Liquid Gas Melting Vaporization CondensationFreezing

Liquid Sublimation Melting Vaporization deposition Condensation Solid Freezing Gas Require energy Release energy

Changes of State Melting Melting point - temperature at which solid and liquid form of substance exist in equilibrium, also called freezing point

Different Boiling points Different substances boil at different temperatures because they have different intermolecular forces – Weak forces- lower boiling point

What is Thermal Energy?

Particles of matter are in constant motion. This motion relates directly to the state of matter of the object (solids, liquids, or gases). Temperature Temperature measures how fast the particles are moving. A higher temperature indicates that the particles are moving faster. Moving particles possess kinetic energy. Temperature Temperature is defined at the average kinetic energy of the particles of an object.

Temperature and Energy, continued All particles have kinetic energy. – All particles in a substance are constantly moving. – As the average kinetic energy of the particles in an object increases, the object’s temperature increases. Common thermometers rely on expansion. – Most substances expand when their temperatures increase. – thermometer: an instrument that measures and indicates temperature Thermostats rely on the expansion of different metals.

Relating Temperature to Energy Transfer, continued Temperature changes indicate an energy transfer. heat: the energy transferred between objects that are at different temperatures The transfer of energy as heat always takes place from something at a higher temperature to something at a lower temperature. The greater the difference in the temperatures of the two objects, the faster the energy will be transferred as heat.

Thermal Energy Thermal Energy is the sum total of all of the energy of the particles of an object. Thermal energytemperature Thermal energy and temperature are related though DIFFERENT. Temperature Temperature is the average kinetic energy of the particles of an object. Thermal energy Thermal energy is the total amount of energy of the particles of an object. A bathtub full of water at 100 o F has more thermal energy than a thimble of water at 100 o F. The temperature is the same but the total amount of energy is different. The bathtub has more energy.

heat What is heat? Heat Heat is thermal energy that flows from something at a higher temperature to something at a lower temperature. specific heat What is specific heat? Specific heat Specific heat is a property of matter which determines how readily a material is to absorb heat and change temperature. Specific Heat Specific Heat is defined as the amount of heat energy needed to raise the temperature of 1 kg of a substance by 1 o C or 1 K.

Did you notice that water has a very high specific heat, whereas iron has a low specific heat? Water requires a lot of heat energy to raise its temperature.

Transferring Thermal Energy How is Thermal Energy Transferred? YOU MUST KNOW THIS!!!!! Conduction Conduction – direct contact Convection Convection – through a fluid Radiation Radiation – by electromagnetic waves

conduction What is heat transfer by conduction? Heat transfers as particles of an object increase their collisions as heated. These collisions transfer the heat energy through the object by colliding with adjacent particles.

convection What is heat transfer by convection? Heat is transferred through a substance through currents. This occurs in fluids (liquids AND gases) Convection Convection currents are caused by heating of a liquid or gas, the liquid or gas rises, then cools and falls. This occurs in the mantle of the earth And in the atmosphere. Most of our weather patterns are the result of convection currents in the atmosphere.

What is heat transfer by radiation? Radiation is heat transfer by electromagnetic waves. These wave may pass through all states of matter and also through NO matter – such as the vacuum of space. This energy is often called radiant energy. Radiant energy from the sun travels through the vacuum of until it reaches the earth.

How is heat flow controlled? Insulators – a material which does not allow heat to pass through it easily. Some animals have good insulation to survive severe winters.

Buildings and houses are insulated so that heat does not pass out of (winter time) and into (summer time).

What are some other uses of insulation?

Using heat – How do we use heat in our lives? Forced-Air Systems – a fuel is burned in a furnace and a fan circulates the heat in the house

Radiator Systems – closed metal containers that contain hot water or steam. The thermal heat is transferred to the air and circulated by convection currents. Electric radiators – heat metal coils which transfer the thermal heat to the surrounding air.

Refrigerators, air conditioners, and heat pumps – how do they work? A coolant is circulated through pipes by a compressor. When the pipes get small and narrow the coolant compresses and changes to a liquid giving off heat energy. When the pipes get larger, the coolant changes from a liquid to a gas (evaporates) causing the area to absorb heat and get cooler Radiator Systems – closed metal containers that contain hot water or steam. The thermal heat is transferred to the air and circulated by convection currents. Electric radiators – heat metal coils which transfer the thermal heat to the surrounding air.

The human coolant – Built-In cooling system The human body has a cooling system which function automatically – perspiration – sweat. Like a refrigeration system, the evaporation of the sweat from the surface of the body causes energy to be absorbed from the skin, causing the skin to feel cooler. No sweat!!!