Temperature Scales: Kelvin, Celsius, Fahrenheit

Temperature Scales

• The diagram shows three thermometers, each labeled with boiling point of water, melting point of water, and absolute zero.
• The Kelvin scale is the most important scale since it is based on absolute zero.
• Absolute zero is -273.15 degrees Celsius.

Conversion of Temperature Scales

• A change of one degree Celsius is the same as a change of 1.8 degrees Fahrenheit.

Thermal Equilibrium

• Two systems at different temperatures, if placed into contact with another, a higher temperature will transfer heat to the lower temperature.
• The system will reach thermal equilibrium, they will then be in the same temperature.

Zeroth Law of Thermodynamics

• "Zeroth law" states that if two systems are in thermal equilibriums with a third system, they are in thermal equilibriums with each other.

Thermometer

• A instrument used to measure temperature.
• There are nine types of thermometers.

Liquid Thermometer

• Some examples of such liquids are mercury, alcohol, and toluene.

Mercury Thermometer

• It consists of a bulb containing mercury attached to a glass tube of narrow diameter filled with mercury and a standard temperature scale is marked on the tube.
• The boiling point of water and melting point of water.
• With changes in temperature, the mercury expands and contracts and the temperature can be read from the scale.

The Alcohol Thermometer

• Consists of a glass capillary tube marked with degrees Celsius or Fahrenheit and containing alcohol which rises or falls as it expands or contracts with changes in temperature.

Thermal Expansion

• Thermal expansion is the tendency of matter to change in volume in response to changes in temperature.
• When a substance is heated, its kinetic energy increases, this increased energy causes the molecules to vibrate more and they are moved further apart from each other.
• Thermal expansion can occur in any dimension of an object, with corresponding effects on its volume.
• All dimensions of the object expand proportionally to the temperature change.
• All materials expand differently depending on the material's structure and properties.
• The thermal expansion of solids are categorized into three types: linear, areal, and volumetric.

Linear Expansion

• Is the change in length of an object when subjected to temperature changes, the increase in length is proportional to the original length.
• L = L0(1+αΔT)
• Where L = final length, L0 = original length, α = coefficient of linear expansion, and ΔT = change in temperature.

Areal Expansion

• The change in the area of a surface when the temperature changes.
• A = A0(1+2αΔT)
• The coefficient of area expansion of a solid, which is approximately twice the coefficient of linear expansion.

Coefficient of Volumetric Expansion

• Is defined as the change in volume per unit original volume per unit temperature change.
• The change in volume is proportional to the original volume and the change in temperature.
• V = V0(1+βΔT)
• Where V0 is the original volume, β is the coefficient of volumetric expansion, and ΔT is the change in temperature.

Calorimetry

• Calorimetry is the branch of thermodynamics that deals with the measurement of heat transfer during physical and chemical processes.
• Heat transfer describes the flow of energy between systems at different temperatures.
• The amount of heat transferred is: Q = m·c·ΔT.

Quantity of Heat

• Heat is a transfer of energy - energy is highly localized.
• Heat transfer describes the flow of energy between systems at different temperatures.
• The increasing temperature is the increase of kinetic energy in the matter of the object.
• The amount of heat transferred is: Q = m·c·ΔT.

Specific Heat Capacity

• The values for the specific heat of some common substances are given in the table.
• Specific heat capacity is the amount of heat energy required to raise the temperature of a unit mass of a substance by one degree Celsius.

Problems

• Various problems related to thermal expansion, calorimetry, and specific heat capacity are provided.