Heat and States of Matter Chapter 9

Temperature and Thermal Energy Section 1

Kinetic Theory of matter All around you objects are warming and cooling What causes the temperature of an object to change? Temperature is related to the motion of the particles of matter than make up an object The Kinetic theory of matter describes the motion of the particles Matter is made up of atoms, molecules, or ions that are constantly in random motion Particles in motion will have kinetic energy When particles collide they will transfer kinetic energy from one particle to another

Temperature Temperature Temperature scales Measure of the average kinetic energy of its particles AS average kinetic energy increases, temperature increases Temperature scales Kelvin (K) SI unit Celsius (oC) Fahrenheit (oF)

Temperature conversions Celsius to Kelvin K = oC + 273 Celsius to Fahrenheit oC = (5/9)(oF – 32) Fahrenheit to Celsius oF = (9/5) oC + 32

Let’s Practice What is -40 o F in degrees Celsius?

Here’s another one… What is the temperature of 22 oC in degrees Fahrenheit?

One more… What is 25 oC in Kelvin?

Thermal Energy Not only are particles in matter constantly in motion, they are attracted to one another AS the particles move further apart, they gain potential energy The sum of all the kinetic and potential energy of all the particles of an object is the thermal energy

Heat Heat Thermal energy that flows from something at a higher temperature to something at a lower temperature Form of energy Measured in Joules Always flows from warmer materials to cooler materials

Specific Heat SPECIFIC HEAT OF SOME COMMON MATERIALS Different objects will change temperature faster than others As a substances is heated, temperature changes depends on: The amount of thermal energy added Nature of the substance Specific heat is the amount of thermal energy required to raise the temperature of 1 kg of some material by 1 oC Measured in J/(kg oC) Substance Specific Heat J/(kg oC) Water 4,194 Ice 2,110 Asphalt 920 Glass 800 Iron 450

Changes in Thermal energy Changes in thermal energy are calculated using the following equation: Q = m x ΔT x C Q = Change in thermal energy (j) M = Mass (kg) ΔT = change in temperature (final temp – initial temp) C = specific heat of the substance

Let’s Try it… The air in a living room has a mass of 72 kg an. d a specific heat of 1,010 J/(kgoC). What is the change in thermal energy of the air when it warms from 20oC to 25oC?

Measuring specific Heat A Calorimeter is used to measure specific heat IN a Calorimeter, a heated sample transfers thermal energy to a known mass of water. The energy absorbed by the water is calculated Energy absorbed = energy released by the sample

States of Matter Section 2

Four states of Matter Solid Liquid Gas Plasma Tightly packed particles vibrating in space Fixed Shape and volume Liquid Attractive forces are weaker than in solid Particles slide past one another allowing flow Definite volume not specific shape Gas Particles are further apart Attractive forces are very weak NO definite volume or shape Plasma Most common Consists of positive and negative charged particles with no definite shape or volume Results from collisions between molecules moving at high speeds

States of Matter

Changing states Changes in thermal energy cause substances to change from one state to another Melting Energy must be added until particles move out of their ordered arrangement Energy required to change 1 kg of a substance from a solid to a liquid is the heat of fusion Melting point is the temperature where as solid starts to melt

Changing states Freezing Energy is released Particles move slower and the attraction between particles increase so that they form an ordered arrangement The amount of energy released is also the heat of fusion Freezingheat released (negative value) MeltingHeat absorbed (positive value)

Changing state Vaporization Particles move faster Attractive forces weaken Particles not longer cling to each other Evaporation occurs at the surface of the liquid Evaporation causes the surface of the liquid to decrease Heat of vaporization is the amount of energy required for 1 kg of the liquid to become a gas at boiling point

Changing state Condensation Gas particles slow down Attractive forces increase Return to liquid state The amount of energy released is also the heat of vaporization Vaporizationenergy absorbed (positive value) CondensationEnergy released (negative value)

Heating Curve of a substance HEATING CURVE OF WATER When the system is heated, energy is transferred into it. In response to the energy it receives, the system changes, for example by increasing its temperature. A plot of the temperature versus time is called the heating curve.

Thermal Expansion Solids, liquids, and gases will expand and contract with fluctuations in temperature Slower moving particles will be closer together smaller volume Faster moving particles will be further apartlarger volume

Transferring thermal energy Section 3

Ways to transfer thermal energy Conduction Convection Radiation

Conduction Thermal energy can be transferred when particles collide This type of energy transfer is know as conduction Particles closest to the heat source speed up, collide with nearby slow moving particles, and ultimately passing energy throughout the sample Required contact

convection Convection is the transfer of thermal energy by movement of a fluid or gas Particles gain energy from heat source. Warm air is less dense and will rise. As warm air is rising, cool air from the side replaces heated air causing a circular convection current.

Radiation Radiation is the transfer of energy by electromagnetic waves Energy transferred by radiation is called radiant energy Radiation can pass through solids, liquids, and gases

Thermal Insulators Thermal insulators are materials in which thermal energy moves slowly Examples of thermal insulators Some plastics Wood Fiberglass Air