Temperature and Heat

Temperature and Heat

1. Temperature

   • is
     • Measure of the average kinetic energy
       • When
         • The average kinetic energy of the molecules goes up, the average speed of the molecules increases
           • Note
             • The average kinetic energy of the molecules of an object is an important part of the concept of temperature and provides some useful intuition what temperature.
               • Molecules
                 • Can have rotational kinetic energy and traslational kinetic energy and the molecules in periodic solids can have collective modes of motion that have energy.
     • A number, is related to energy, but it's not energy itself. ( it's a proportional to a type of energy)
       • Temperature can be measured in a variety of units
     • Directly proportional to the pressure.
       • Note
         • Ordinary gases don´t behave exactly as ideal gases and are better described by the van Waals equation of state, but as they are extrapolated to xero pressure (The same value for zero of the K scale.
   • Terms of entropy
     • If there are more ways to accomplish a given state of a system of particles, then other states will spontaneously transition to that sate over time is the transition is consistent wich conservation of energy.
   • Note
     • Temperature is not directly proportional to internal energy since temperature measure only the K.E.. part of the internal energy.
       • so
         • Two objects with the same temperature do not general have the same internal energy.
   • Scales
     • The Celsius, Kelvin and Fahrenheit temperature scales.
       • PD.
         • Kelvin scale is called absolute temperature and the Kelvin is the SI unit for temperature
         • The Rankine Scale
           • For
             • Engineering purposes
               • Degree size is the same as the Fahrenheit, and zero of scale is absolute zero.
       • Temperature Standard Points
         • By International agreement, one standard point is the triple point of water wich has been defined to be 273.16K. The freezing point of wates at atmospheric is .01K below this at 273.15K

2. Heat

   • is
     • Thermal energy transferred from a hotter system to a cooler system that are in contact
       • calculate
         • The heat released or absorbed using:
           • The
             • The mass of the substance
             • The specific heat capacity of the material
               • The heat capacity of water does change slightly with temperature
             • Change in temperature
             • "Q" is the quantity of heat transferred to or from the object
     • Measurement of some of the energy in a substance
       • Units
         • Heat ussed Joules or other energy units
   • When
     • Heat goes into a subtance one of two thing can happen:
       • 1.-The substance can experience a rise in temperature.: The heat can be realized as an increases in the average K.E.
         • Note
           • That this increases in the average K.E. of the molecules means: They will now be traveling faster than before the heat arrived
       • 2.- The substance can change state..The energy is used to change the bonding between the molecules.
         • Note
           • When heat comes into a substance, energy comes into a substances.
   • Mechanical Equivalent
     • Heat flow and work are both ways of transferring energy
       • Calories were the accepted unit of heat and joulse became the accepted unit of mechanical energy.
         • The British Thermal Unit was also indroduced
   • Changes of state
     • The heaat gained or lost by an object to the resulting temperature changes of that object, but there is not temperature change.
       • List several states changes:

3. Zeroth Law of thermodynamics

   • says
     • No heat is transferred between two objects in thermal equilibrium; they ara the same temperature.
   • consider
     • Threee ibjects, say blocks of cooper, iron and alumnium wich are in contact such that they come to thermal equilibrium
       • Equilibrium we mean that they are no longer transferring any net energy to each other.
         • They are the same temperature, and that temperature is a property of these objects.
           • The collection with higher K.E. has a higher temperature, and that net energey transfer will be from the higher temperature collection to the lower temperature collection, and not vice versa

4. Diferrence between both

   • They are related, but not identical ideas.

5. Internal Energy

   • is
     • Energy associated with the random, disorded motion of molecules.
       • associated
         • Moving objects;it refers to the invisible microscopic energy on the atomic and molecular scale.
           • Note
             • U is the common symbol used for internal energy
             • Molecules traveling at hundreds of meter per second

6. Thermal Expansion

   • is
     • Relationships for length, area, and volume in terms of the linear expansion coefficient.
   • Linear Expansion
     • is
       • Long thin rod can be reasoned out as follows:
     • Area Expansion
       • Is
         • Order of parts per million per degree.
       • Volume Expansion
         • Over small temperature ranges.
   • The Expansion of Water
     • The fact that water expands upon freezing causes icebergs to float (Density at about 4°C).
       • Part of the phases changes keeps the ice floating with 8% of its mass above the surface.
     • The Expansion upon freezing comes from the fact that water crystallizes into an open hexagonal form
       • The hexagonal lattice contains more space than a liquid state. The hexagonal ice is primary form of ice and is the domidant form the freezing point at 273K down to about 72K, 13 difference crystalline forms, and been according to Debenedetti and Stanley
     • Water Density
       • Ordinary temperatures contracts and increases in density as it is cooled, like most substances.
         • note
           • 4°C it reaches maximum density.
             • PD.
               • Watter provides the standard for density at 1 gram/cm3

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