Physics 2


4.1 Thermodynamics

  • science that deals with the relationship between heat and other form of energy.

  • Greek words “therme” = heat and “dynamics” = power.

  • coined by the english physicist, James Prescott Joule (1849).

  • 1842, Nicolas Sadi Carnot → Father of Thermodynamics → published “Reflections on the Motive power of fire” → discourse on heat, power and engine efficiency.

Branches of Thermodynamics:

  1. Classical Thermodynamics → branch concerned with thermodynamics states and properties (energy, work and heat) and with the laws of thermodynamics without the atomic interpretation. (macroscopic approach)

  2. Statistical Thermodynamics → branch that includes atomic and molecular theories. (microscopic approach)

  3. Chemical Thermodynamics → branch concerned with the study of the interrelation of heat with chemical reactions or with a physical change of states within the confines of the laws of thermodynamics.

Phases of Substances

  1. Solid → substance does not take the shape or volume of the container.

  2. Subcooled Liquid → liquid is non-saturated. (non-saturated = not at its boiling point)

  3. Saturated Liquid → liquid can absorb as much heat as it can without vaporizing.

  4. Liquid-vapor mixture → liquid and vapor co-exist with the same temperature and pressure.

  5. Saturated vapor → vapor has absorbed more heat than necessary to vaporize it.

  6. Ideal gas → the gas (a highly superheated vapor) behaves in accordance with the ideal gas law.

  7. Real gas → the gas does not behave in accordance with the ideal gas law.

  8. Gas Mixture → two or more gases mixed together freely.

  9. Vapor/Gas mixtures → two or more gases mixed freely with water vapor.

Temperature

→ degree of hotness or coldness of a certain substance with respect to some standard value.

→ dependent on the substance’s energy content,-. ( measure of the average kinetic energy of the different particles in a sample matter.

→ property being measured by the thermometer or a thermoscope.

thermometer or thermoscope → any device that measures temperature.

Temperature Scales:

4 very common temperature scales used:

  1. Celsius scale → AKA Centigrade scale, most widely accepted temperature scale used globally. → there are 100 degrees of separation between freezing and boiling point of water. centigrade= 100 steps. named after Swedish astronomer → Anders Celsius.

  2. Fahrenheit scale →German physicist → Gabriel Daniel Fahrenheit → First inventor of the first mercury thermometer → 180 degrees of separation.

  3. Kelvin scale → SI unit of temperature and most common unit adopted in the scientific community. similar to Celsius scale → 100 degrees of separation between freezing and boiling point. → 0K=273 units colder than its equivalent value in the Celsius scale. 0K= absolute zero temperature.

    absolute zero temperature → lowest temperature any matter can reach or it is the temperature below which any other value has no physical significance.

    → Sir William Thomson or Lord Kelvin.

  4. Rankine scale → William John Rankine.

    → absolute scale equivalent of the Fahrenheit scale. there are 180 degrees of separation between the boiling point and the freezing point.

Thermal Expansion

Two types of expansion → linear and volume.

Solid → both expansion types are significant

Liquid & GAs → volume expansion is significant.


Expansion by Length (Linear Expansion ) → dimension that increased is the length. the change in length increases linearly with the change in temperature.

Expansion by Volume (Volume Expansion) → expansion in3D (three dimensions), not just length. the only type of expansion considered for fluids (liquids/gases).

Heat

Heat → internal energy in transit from one body of matter to another by a virtue of a temperature difference between them.

→ units : kilocalorie and BTU (British thermal unit). 1 kilocalorie (1kcal or Cal ) is the amount of heat required to raise the temperature of 1kg of water by 1°C.

British Thermal Unit (1 BTU) → the amount of heat need to raise the temperature of 1 lbm of water by 1 °F.

HEAT CAPACITY AND SPECIFIC HEAT CAPACITY

Heat Capacity (C)

→if heat is applied, its temperature increases in proportion to the amount of heat transferred.

→ as heat is removed, its temperature decreases in proportion of the amount of heat removed.

Specific Heat Capacity (C)

→ ratio of the amount of heat required to raise the temperature of a unit mass of a substance by one unit of temperature to the amount of heat required to raise the temperature of a similar mass of a reference material, usually water, by the same amount.

Molar specific heat (Cm) → product of the molecular weight and the specific heat of the substance.

Latent Heat (QL) → quantity of heat absorbed or released by a substance undergoing a change of state, such as ice changing to water or water to steam, at constant temperature and pressure.

Different types of latent heat:

  1. Latent heat of fusion → amount of energy supplied to a given substance to change from solid to liquid and vice versa.

  2. Latent heat of vaporization → amount of energy that must be supplied to a given substance to change form liquid to gas and vice versa.

  3. Latent heat of sublimation → amount of energy supplied to a given substance to change from solid to gas without becoming liquid and vice versa.