Unit 12: Temperature and Thermal EnergyThermodynamics is the study of heat

transformations into other forms of energy.◦Used to develop higher performance

products:

Unit 12: Temperature and Thermal EnergyAtoms/molecules collide and trade

energies.◦Linear kinetic energy◦Rotational kinetic energy◦Potential energy

Unit 12: Temperature and Thermal EnergyPut a helium balloon in the sun. Does it

get larger or smaller? What if you put it in the refrigerator?

It gets larger in the sun because molecules keep bouncing off of each other. The colder it is, the slower the motion of the molecules.

Unit 12: Temperature and Thermal EnergyParticles in a hot object have greater

kinetic and potential energies than particles in a cold object do.

This means hot objects have greater average thermal energy than a similar cold object.

Unit 12: Temperature and Thermal EnergyTemperature depends only upon the

average kinetic energy of the particles in the object.

How do you measure your own body temperature?

Unit 12: Temperature and Thermal EnergyMeasuring body temperature:

1. Your body is hot compared to the thermometer

2. Particles in your body have greater thermal energy and are moving faster than the particles in the thermometer.

3. Fast moving particles collide with slow moving particles.

4. Energy is transferred from your skin to the thermometer by the process of conduction (the transfer of kinetic energy when particles collide).

Unit 12: Temperature and Thermal Energy As particles in

thermometer gain more energy, the body particles lose energy and ultimately the thermometer and your body are at the same temperature.

Unit 12: Temperature and Thermal Energy You have reached

thermal equilibrium, the state in which the rate of energy flow between two objects is equal and the objects are at the same temperature.

Unit 12: Temperature and Thermal Energy Temperature Scales:◦ Celsius vs. Kelvin

Celsius is good for day to day measurements Celsius is not conducive for working on science and

engineering problems because it has negative temperatures which implies negative kinetic energy.

Kelvin is based upon absolute zero (the point of lowest internal energy, or for our purposes, the lowest temperature is 0 K.)

◦ TC + 273 = TK

Examples: Convert to Celsius/Kelvin155 K 78 ˚C

Unit 12: Temperature and Thermal EnergyHeat is the energy that is transferred

between two objects that come into contact with each other.◦Heat flows from the hotter object to the

cooler one.◦Q represents heat◦Heat is measured in joules.

If Q is negative, heat has left the object If Q is positive, heat has been absorbed by the

object.

Unit 12: Temperature and Thermal EnergyConduction: the

transfer of heat when two objects come into direct contact with one another.

Unit 12: Temperature and Thermal EnergyConvection: the

motion of fluid in a liquid or a gas caused by temperature differences.

Unit 12: Temperature and Thermal EnergyRadiation: the

transfer of energy by electromagnetic waves.

Unit 12: Temperature and Thermal EnergySpecific heat of a material is the

amount of energy that must be added to the material to raise the temperature of a unit mass by one temperature unit. ◦Represented by C. ◦Units are the J/kg·K

Unit 12: Temperature and Thermal EnergySome objects are easier to heat than

others.Example: it take 897 J of energy to raise

1 kg of Al 1K.

Unit 12: Temperature and Thermal EnergyHeat transfer, Q is equal to the mass of

an object times the specific heat of the object times the difference between the final and initial temperatures.

Q = mCΔT = mC(Tf - Ti)

Unit 12: Temperature and Thermal EnergyExample:

Sometimes a short circuit in an electrical wiring system can produce enough heat to melt a wire. How much heat must be transferred to a 20.0 g piece of copper wire (C = 385 J/kg·K) in order to raise it from room temperature (25.0 ˚C) to its melting temperature (1082.0 ˚C)? (8140 J)

Unit 12: Temperature and Thermal EnergyConservation of Energy: In an isolated,

closed system, the thermal energy of object A plus the thermal energy of object B is constant.

EA + EB = constant

Unit 12: Temperature and Thermal EnergyA calorimeter is an

isolated, closed system used to measure changes in thermal energy.

Unit 12: Temperature and Thermal EnergyExample:

A 0.025 kg block of copper (C = 385 J/kg·K) at a temperature of 82˚C is added to a calorimeter containing 0.025 kg of water at a temperature of 22˚C. What is the temperature of the copper block and the water when they reach thermal equilibrium?