Thermal Energy All substances are made up of atoms molecules The molecules carry energy in the form of kinetic energy and potential energy The total energy kinetic potential is called the thermal energy or internal energy Cold water Lower temperature Less thermal energy Boiling water Higher temperature More thermal energy Thermal energy depends on the temperature of substance higher temperature higher thermal energy Thermal energy also depends on the amount of the substance The number of atoms molecules that make up the substance 2 gallons of boiling water has twice as much thermal energy as 1 gallon of boiling water Thermal Energy vs Temperature If you spill a cup of boiling water on your hand large mass large thermal energy vs If a small drop of boiling water lands on your skin small mass small thermal energy Temperature The quantity that measures how warm or cold an object is Hot and cold is a relative term Temperature measures the average kinetic energy of the molecules that make up the object Which has more temperature a red hot tack or a cool lake The tack Which has more thermal energy The lake more molecules Temperature is proportional to the average translational kinetic energy per particle in a substance Gas how fast the gas particles are bouncing to and fro Liquid how fast particles slide and jiggle past one another Solid how fast particles move as they vibrate and jiggle in place Measure temperature Rely on the fact that objects expand when heated and contract when cooled There are exceptions Use some properties of a substance as a reference Freezing 0 Celsius and boiling 100 Celsius points of water Absolute Zero Is it possible to have negative temperatures Yes Is there a limit of how low the temperature can be Yes Is there a limit of how high the temperature can be No Kelvin Scale Absolute Zero Kelvin scientific temperature scale Absolute Zero Lowest possible temperature Kelvin 0 K 273 Celsius No thermal energy Divisions are identical to the Celsius scale When calculating Kelvin temperatures from the C add 273 Freezing point of water 0 C 273 K Boiling point of water 100 C 373 K Room temperature of water 22 C 295 K Kelvin is the standard unit of temperature Use either Celsius or Kelvin when working with temperature differences Use ONLY Kelvin when working with a specific value of temperature Internal Energy Thermal Energy Grand total of energies in a substance including kinetic and potential energies Directly proportional to the temperature in Kelvin Directly proportional to the number of molecules that make up that material What Does it Mean for Temperature to Change Raise the temperature add energy to the molecules They move faster Lower the temperature remove energy from the molecules They move slower How do you add or remove energy Why Do Objects Feel Hot or Cold to the Touch Transfer of energy to or from your body Cold objects when you touch the object thermal internal energy is removed from your body because your body is at a higher temperature than the object Your brain registers this as cold Hot objects when you touch the object thermal internal energy is transferred to your body because your body is at a lower temperature than the object Your brain registers this as hot Energy is always transferred from the higher temperature object to the lower temperature object Changing the Temperature Ice is in contact with the can Energy flows from the high temperature can to the low temperature ice The can s temperature drops The ice s temperature rises The process stops when the temperatures are equal thermal equilibrium Heat The flow of energy from a high temperature object to a low temperature object Energy in transit Measured in joules J or calories cal or Calories Cal Conversion 1 cal 4 186 J Conversion 1000 cal 1 Cal 4186 J What Will Affect How the Temperature of an Object Changes How much energy you transferred to or from the object Heat added or removed Q The longer you leave a pot of water on the stove top the warmer the water gets because you have added more heat or energy How much of the substance you have Mass m A pot of water with less water changes temperature by a greater amount than one with more water The amount of temperature change you get depends on three things The quantity of heat transferred Q J or cal The mass of the object m kg or g The specific heat of the material c J kgc or cal gc T Q mc Big change in temperature smaller heat capacity Specific Heat Capacity The larger the specific heat capacity the smaller the change in temperature for the same quantities of mass and heat transferred Capacity how much it can contain The metaphor means this water has MORE capacity than silver which means water can absorb MORE joules of heat with a LOWER temperature change Defined as the quantity of heat required to change the temperature of a unit of mass of a substance by 1 degree Celsius c Q m T Water m 1 kg T 1 Celsius Q 4186 J c water 4186 J kgc Example You wish to increase the tempertaure of your hot chocolate mass 1 kg by 4 5 degrees Celsius How much heat is required Assume the hot chocolate is made up primarily of water water has a specific heat capacity of 4186 J kgc An unknown substance is sent to your lab for testing Its mass is 5 kg You find that adding 43 000 J of heat raises its temperature by 10 degrees Celsius What is its specific heat capacity Specific Heat Capacity of Water Water has a very high specific heat capacity A great amount of heat is required to change the temperature of water Keeps the earth at moderate temperatures Keeps our bodies at moderate temperatures Calorimetry Under ideal conditions when two objects at different temperatures are mixed together the heat lost by the higher temperature object is gained by the lower temperature object Cool milk added to coffee Hot metal in a forge submerged in water Ice cubes added to tea Example A 75 gram piece of unknown material is heated to an initial temperature of 65 C The material is placed in 150 grams of water that was initially at 15 C When the system reaches equilibrium the temperature of the mixture is 20 C What is the heat gained by the water m 150 g T 5 C c 1 cal gC Q mcT Q 150 1 5 Q 750 cal What must be the heat lost by the unknown substance 750 cal What is the specific heat of the unknown substance m 75 g T 45 C Q 750 cal Q mcT 750 75 c 45 750 3375 c c 0 22 cal gC Thermal Expansion Due to rise in temperature of a substance molecules jiggle faster and move farther apart Most