Chapter 4: Heat and Temperature Summary

Chapter 4: Heat and Temperature Summary

Matter

There are three phases of matter: Solid, Liquid and Gases.

State   Characteristic	Solid	Liquid	Gas
Shape	Definite	Indefinite	Indefinite
Volume	Definite	Definite	Indefinite
Movement Allowed	Vibration	Vibration, Rotation and Limited translation	Vibration, rotation and translation
Atom/Molecules	Stationary and in contact	Mostly in contact	Mostly not in contact

 

Molecular Motions

• Characterized by Kinetic Energy (KE). Temperature is a measurement index for the KE.
• Illustration

1. Faster diffusion of gases at high temperature
2. Expansion and contraction with temperature changes

Temperature

• Refers to the internal energy of an object (Average kinetic energy)
• Measured using thermometer whose functionality depends on thermometric properties e.g., thermostats and bimetallic.
• Thermometric scales used include Fahrenheit, Celsius and Kelvin.
• Conversion to either scale from another is as shown;

T_F= Fahrenheit to Celsius

T_C=Celsius to Fahrenheit

T_K= Celsius to Kelvin

 

Heat

• Internal Energy transferred from one point to another due to differences in temperature or energy form conversion.
• External energy (E)= Total potential E. + Total Kinetic E. (of an object)
• Internal E. = Total Kinetic E.
• Change from external to internal energy results in Temperature increase
• Specific heat refers to heat energy required to raise the temperature of 1 kg object by one degree Celsius
• Heat transfer is by conduction, convection or radiation
• Conduction involves heat transfer in solids through atom collision hence cannot occur in vacuum
• Convection is heat transfer by bulk movement of hot material such as rising of hot air in natural convection
• Energy transfer through electromagnetic waves and hence can occur in a vacuum. Temperature determines emission rate, light intensity and radiation type.

Evaporation: involves overcoming of cohesion force by molecules that then escape

Condensation: involves losing of KE by gas molecules that merge to liquid

Thermodynamics

• Study of heat and its relationship to mechanical and other energy forms
• Involves consideration of the system, surroundings and internal energy
• Laws of thermodynamics

1^st Law: Conservation of energy- heat is not lost but is converted from one form to another. Considers internal energy

2^nd Law: Comprises three parts;

1. No heat to work is 100% efficient- some energy is lost.
2. A cold body requires work to heat hot body.
3. Entropy of an isolated system always increases