This document discusses concepts related to energy and heat. It defines temperature and explains that temperature is related to the kinetic energy of atoms and molecules. It explores the relationship between energy, work, and heat, noting that heat refers to the transfer of energy between systems with a temperature difference. The document also discusses historical theories of heat and caloric and introduces the modern idea that heat is related to the motion of particles and internal energy of a system.

1. ENERGY & HEAT
Why sometimes it’s hot and others it’s cold

2.  What is Temperature?
 Where is Heat?
 Is there a relationship between Energy, Work & Heat?
 How do Energy and Heat relate to each other?
 What effects does Heat have in matter?
 An old theory about Heat
 A modern idea about Heat
 A new kind of Energy: Internal Energy
 Internal Energy and States
A Guide to Heat

3.  Temperature is what we usually measure with
thermometers
 A thermometer is a device designed to be put in contact
with another object and get a number because it has
been previously calibrated in a certain scale
 A usual standard temperature scale in Europe and other
countries is the CENTIGRADE or CELSIUS (°C) scale,
where 0 °C is the ice melting point at 1 atm of pressure,
and 100 °C is the water boiling point at the same
pressure
 We will soon learn that, in fact, temperature deals with
the kinetic energy of atoms and molecules of which
matter is composed
What is Temperature?

5.  While all physical systems do have amounts of energy,
they do not have any work neither heat at all
 Concepts like work or heat refer to a PROCESS, and
cannot be held by any system
 Work is a form of changing one system’s energy by means
of a macroscopic FORCE acting along a macroscopic PATH
 Sometimes, one system’s energy can change due to
macroscopic forces but without any macroscopic motion
 Heat happens when energy is transferred without any
macroscopic changes because it is transferred to each
one of its particles moving in a chaotic way
Where is Heat?

6. Is there a relationship
between Energy, Work & Heat?

7.  We have already seen the way how WORK & ENERGY are related:
W = DE
 In fact, the same relationship can be applied to HEAT & ENERGY:
Q = DE
 That is true, because heat is nothing but a different form of
transferring Energy between two systems with a temperature
difference
 It is a main idea in science, that if we put together two systems
originally at a different temperature (one HOT and the other
COLD), ENERGY SPONTANEUSLY FLOWS FROM THE HOT TO THE
COLD BODY UNTIL THEY ARE IN THERMAL EQUILIBRIUM, and
the contrary never happens
How do Energy and Heat
relate to each other?

8.  As a process to transfer energy, heat can have many
different effects on bodies:
 It changes its temperature: when a body gains energy
by means of heat, its temperature raises
 If temperature approaches a change of state, then
the solid body melts or the liquid boils
 When a body loses energy by means of heat, its
temperature descends, and changes in state can
happen in the contrary sense
 In all situations, changes in temperature due to heat
transference change the volume of bodies (specially
in gaseous state), what is known as dilatation
What effects does Heat
have in matter?

9.  Former scientists (XVIII C) imagined that the effect of heat
and temperature should be related to an INVISIBLE FLUID
they called CALORIC
 The idea allowed them to do some measures of heat and
temperatures, design thermometers and calorimeters, and
define the early classical unit for Heat: CALORIE (cal)
 But some issues avoided this idea to be acceptable: if
caloric was a fluid, that meant to be some sort of matter,
then it should have weight. Cold and hot bodies should
have a different mass, and that never happens. If we melt
1 g ice, we always get 1 g water, not any more nor less
 It also seemed to be inexhaustible, because in many
experiences something strange happened: the more
caloric you got from a body, the more remained inside it
An old theory about Heat

10. Ice calorimeter designed
by Lavoisier and Laplace

11.  A modern theory about heat comes from a key idea:
matter is made up of very tinny particles (atoms,
molecules…) constantly moving according to different
degrees of freedom
 In gases particles have practically infinite freedom to
move around, in liquids particles also move almost
freely but not totally free, while in solids particles can
hardly do but vibrate around an equilibrium position
 Temperature is a measure of the mean kinetic energy
of a set of particles that constitute any kind of matter
 There is a NATURAL TEMPERATURE SCALE (KELVIN
SCALE) where ABSOLUTE ZERO (0 K) would mean NO
MOTION AT ALL. That temperature equals to −273 °C
and is in fact impossible to reach
A modern theory about Heat

12.  Heat (Q) is similar to work. It relates to changes in energy
of bodies. But Heat changes INTERNAL ENERGY (U) :
Q = DU
 INTERNAL ENERGY is the addition of all types of energy
in a certain amount of particles
 It includes kinetic energy due to all sorts of motion
(translation, vibration, rotation…) and potential energy
due to all electrostatic interactions between them
A new kind of Energy:
Internal Energy

13. Internal Energy and States