Presentation on theme: "Thermal Energy & Thermodynamics"— Presentation transcript:
1Thermal Energy & Thermodynamics Chapter 7Thermal Energy & Thermodynamics
2Thermal EnergyThe kinetic energy of the molecules in a solid, liquid or gasThe more kinetic energy, the more thermal energy the object possessesPhysicists also call this the internal energy of an object
3Temperature A measure of how hot or cold something is Measured with a thermometerCelsius Scale sets freezing point of water at 0o and the boiling point at 100oFahrenheit Scale sets freezing point of water at 32o and the boiling point at 212o
4Temperature ScalesTemperature is measured using the Fahrenheit, Celsius, and Kelvin temperature scales.The reference points are the boiling and freezing points of water.
5TemperatureTemperature is proportional to the average kinetic energy of the molecules in a substance.If all the atoms or molecules in a substance are the same, then we are saying
6Absolute ZeroThere is no upper limit to temperature based on the equation.What if the average speed of an atom or molecule in a substance is zero?Must mean a temperature of zero!!!There is an absolute zero of temperatureHow to determine what it is?
7Absolute ZeroWe define a new temperature scale shifted from Celsius by 273o degrees. This is called the Kelvin scale. Water freezes at 273o K and boils at 373o K.
9Heat Touch something hot and thermal energy enters your hand Touch something cold and thermal energy leaves your handDirection of energy flow is from hot to coldHeat is the thermal energy transferred due to a temperature difference
10EquilibriumThermal energy transfers between two objects until the reach the same temperatureThis means until the average kinetic energy of the atoms and molecules is the same
11Quantity of Heat Heat is a form of energy It is measured in joules Common usage is a heat unit called the calorie (the energy needed to raise the temperature of 1 gram of water by 1o CChemists use the kilocalorie (1000 calories=4200 Joules)Nutritionists call it a food Calorie
12First Law of Thermodynamics Whenever heat flows into or out of a system, the gain or loss of thermal energy equals the amount of heat transferred.A system is substance, device or well-defined group of atoms or moleculesThis Law is just our old friend Conservation of Energy
13Second Law of Thermodynamics Heat never spontaneously flows from a cold substance to a hot substance.This really says that systems tend to a state of more disorder or greater entropyRead the discussion of entropy on page 167 in your textbook
14Third Law of Thermodynamics No system can reach absolute zero.
15Specific Heat Capacity Different substances require different amounts of heat to change temperature by a given amountDue to differences in internal structure of the molecules and how they are bound in the substance
16Specific Heat Capacity The specific heat capacity of any substance is defined as the quantity of heat required to change the temperature of the substance by 1o Celsius.Water has a high heat capacity which is very usefulIt accounts for climatic conditions on the west coasts of continents in the northern hemisphere
17Thermal ExpansionAt higher temperatures, molecules have more kinetic energy and on average move farther apart from each otherThis means the substance expandsAmount of expansion depends on the structure of the substance