Temperature and Thermal Energy

TemperatureTemperature – average K.E. of the particles in a sample.

Depends on the size of the particles and their velocity (½ mv2).Temperature Ave. K.E. of particles Does not depend on the mass of sample : (total number of particles).

Measure using a thermometerCelsius : °C

Water freezes at 0°CWater boils at 100°C (at 1 atm pressure)

Kelvin : KWater freezes at 273.15 KWater boils at 373.15 K (at 1 atm pressure)T = 273.15 + TC

Fahrenheit : °FWater freezes at 32°FWater boils at 212°F (at 1 atm pressure)

Kelvin was developed to work with gases. No negative temperatures.Absolute zero : 0 K, lowest temperature, no motion of particles (or anything).

Internal EnergyKinetic Molecular Theory – matter is made up of tiny particles that are in constant motion.

States of Matter – solids, liquids, gases, plasmaState of matter depends on the temperature and the forces holding the particles together.

Internal Energy – the total amount of energy of the particles in a sample.

Symbol : UUnits of Joules, JDepends on:1. Kinetic energy of the particles

(temperature)Translational, Rotational, Vibrational

2. Mass of sample (number of particles)

HeatTransfer of energy between two objects because of a difference in their temperatures.Heat flows from hot objects to cold objects.Changes the internal energy (U) and the temperature (T) of the sample.Symbol : QUnits : Joule (J)

calorie (cal) = 4.186 JCalorie (food calorie) = 1 kcal = 4.186 kJBritish thermal unit (Btu) = 1.055 kJ

Transferring EnergyEnergy is transferred by conduction, convection, and radiation.Conduction – transfer of the K.E. when particles collide. Matter must touch.

Works best in solids.Thermal conductors – metalsThermal insulators - wood

Convection – transfer of energy because of the movement of fluids.

Fluids move because of a change in density.Hot air rises, cold air settles.Causes changes in weather.Works best in liquids and gases.

Sea Breeze

Land Breeze

Radiation – transfer of energy by electromagnetic waves.

Solar energy - no matter is needed.Energy is absorbed and then the matter gets warm.

Thermal EquilibriumThermal Equilibrium – the rate that energy flows from one sample to another is the same as the rate the energy flows back.

Objects have the same temperatureObjects may not have the same internal energy

Place a hot metal into cold water, they have reached thermal equilibrium when they reach the same temperature.One object lost energy and one object gained energy.

Specific Heat Capacity

Substance Specific HeatJ/kg°C

Ti

°CTf

°CT°C

Copper 385 25 37.99 12.99

Aluminum 903 25 30.54 5.54

Methanol 2450 25 27.04 2.04

Water 4186 25 26.20 1.20

Hydrogen 14,298 25 25.35 0.35

Add 5000 J of energy to 1.0 kg of each of the following substances.

Specific Heat Capacity – the amount of energy required to raise 1 kg of a substance 1°C.The capacity of a substance to absorb energy for given change in temperature.Symbol : Cp (constant pressure)

Units : CkgJ

Substances with high Cp will absorb large amounts of energy for a given temperature change. Substances with a low Cp can only absorb a small amount of energy for the same temperature change. Water is used as a coolant because it can absorb large quantities of heat without a large change in temperature.Hydrogen is also a good coolant, but it is explosive!

You bite into a hot pizza that just came out of the oven. The crust and the toppings are all at the same temperature. The roof of you mouth is burned, but you tongue is not. Why?Topping is mostly water, it contains more energy than the crust because it has a higher capacity of heat than the bread that has very little amount of water.

One to remember!

Specific Heat   Specific Heat

Substance J/kg °C Substance J/kg °C

Aluminum 903 Lead 130Brass 376 Methanol 2450

Carbon 710 Silver 235Copper 385 Steam 2010Glass 664 Zinc 388Ice 2090 Water 4186Iron 450    

The amount of energy transferred as heat depends on the specific heat capacity, the mass and the change in temperature.

Q = mCpT Q = mCp(Tf – Ti)Tf > Ti gaining energy +Q (getting hot)Tf < Ti losing energy -Q (getting cold)Cp for water is 4186 J/kg°C.