Chapter 1: Temperature and Heat – Study Notes

C1.1 Sensation of hotness and temperature

• Activity 1 (perception of temperature):
  • Place one hand in cold water and the other in hot water for a couple of minutes, then place both hands in warm water.
  • Observation: Each hand will feel a specific sensation due to heat transfer direction.
• Generalization about heat sensation:
  • Our sense of heat tells us whether heat energy is leaving the skin (cold sensation), entering the body through skin contact (hot sensation), or both depending on the situation.
• Question on absolute hotness:
  • Is there such a thing as absolute hotness? Hotness is relative to the observer’s sensation; therefore, absolute hotness cannot be determined by sensation alone.
• Temperature as an absolute measure:
  • Scientists define temperature as the degree of hotness of a body, a property that can change and be measured.
  • Physical changes tend to occur at the same temperature anywhere in the universe, given the same external conditions (e.g., at 1 atm, water boils at 100°C on Earth).
  • Question: At the same pressure (1 atm), would water boil at the same temperature on the Moon? (Implied: yes, it would boil at 100°C if the pressure is 1 atm there too, but lunar atmospheric conditions differ.)
• Thermometric properties and thermometers:
  • Thermometric properties are properties of objects that can be used to make thermometers (e.g., the change of volume of a fixed-mass gas at constant pressure).
  • Not every property that changes with temperature is a thermometric property; thermometric properties must be measurable and vary with temperature in a well-defined way under the same conditions.
  • Examples of thermometric properties include the expansion of gases, liquid column rise in thermometers, etc.
• Conceptual aim (Chapter 1): Temperature and Heat
  • Introduction to how temperature relates to heat transfer and measurement.

C1.1 Key concepts to remember

• Temperature: a quantitative measure of hotness/coldness; objective but measured via thermometric properties.
• Absolute temperature: an objective scale (Kelvin) linked to thermodynamic properties; independent of the particular thermometric liquid.
• Thermometric properties: measurable properties used to define temperature scales.

C1.2 Temperature scale

• Ice point and steam point (at 1 atmosphere):
  • Ice point = 0°C (the thermometer reads 0°C when in thermal equilibrium with melting ice at 1 atm).
  • Steam point = 100°C (the thermometer reads 100°C when in thermal equilibrium with steam above boiling water at 1 atm, i.e., 1.01 × 10^5 Pa).
• Calibration of a Celsius thermometer (experiment outline):
  • Use a mercury-in-glass thermometer to construct a Celsius scale.
  • Ice point corresponds to 0°C; steam point corresponds to 100°C.
  • Define ice point distance and steam point distance on the thermometer stem; plot a temperature axis (vertical) against a length axis (horizontal).
  • The size of a degree Celsius is 1/100 of the temperature difference between the ice point and the steam point; the same difference in the thermometric property corresponds to the same scale interval.
• Terminology:
  • Ice point: mercury level at equilibrium with melting ice at 1 atm; defined as 0°C on the Celsius scale.
  • Steam point: mercury level at equilibrium with steam above boiling water at 1 atm; defined as 100°C on the Celsius scale.
• Safety, apparatus, and types of thermometers:
  • Thermometers types encountered: mercury-in-glass, alcohol-in-glass, thermocouple, bimetallic strip.
  • The experiment checks calibration and is an opportunity to discuss laboratory safety (hazards listed later in the notes).
• Activity 3: Identify the thermometric property used in each thermometer (mercury-in-glass, alcohol-in-glass, thermocouple, and bimetallic strip).
• Step-by-step procedure (summary): 1) Mark the ice point on the thermometer. 2) Mark the steam point. 3) Ensure the thermometer bulb is just above the surface of boiling water to read steam temperature (avoid submerging to read water temperature). 4) Read the thermometer once the reading stabilizes and record it. 5) Measure the barometric pressure in the room. 6) Answer questions about calibration and the implications of non-760 mm readings.
  • Follow-up questions explore how deviations in barometric pressure affect the interpretation of the Celsius scale.
• Practical notes:
  • Steam can cause burns; never touch hot flasks or glassware during experiments. Follow safety precautions for handling hot equipment and steam.
  • This experiment emphasizes the manipulative skills and safety awareness necessary in the laboratory.
• Graphical calibration (Celsius scale):
  • Measure the distance from the bottom of the thermometer to the ice point (L_ice).
  • Measure the distance to the steam point (L_steam).
  • On graph paper, plot temperature axis (vertical) vs. thermometer length axis (horizontal).
  • The scale is designed so that 1 degree Celsius corresponds to a fixed fraction of the ice-to-steam length difference.

C1.2 Temperature scale – highlights and concepts

• Limitations of Celsius scale:
  • The Celsius scale depends on the thermometric agent (e.g., mercury vs. alcohol), which can behave differently with temperature.
  • If readings from two liquids are aligned at ice and steam points, they may diverge at other temperatures.
• Ideal gas as thermometric agent:
  • All ideal gases behave similarly, making them good candidates for defining a physically meaningful temperature scale.
  • Boyle's law (for ideal gases) provides a universal relationship at equal temperatures: the quantity pV is constant for a fixed amount of gas at a fixed temperature.
• Boyle's law (contextual introduction):
  • Experiment setup with a strong glass tube and Bourdon gauge to measure pressure and volume of a fixed mass of gas at constant temperature.
  • Observations: As pressure increases, volume decreases; the product pV remains approximately constant.
  • Practical data can be tabulated (P in kPa, V in cm^3) and used to show pV = constant.
• The Kelvin scale (absolute temperature):
  • Governing equation: $pV = C T_K$ where C is a constant depending on the amount of gas (moles).
  • Absolute temperature T_K is defined such that the ice point corresponds to 273.15 K and the steam point corresponds to 373.15 K; the difference is 100 K between these two fixed points.
  • Transformation between scales: $T<em>K = T</em>C + 273.15$ and equivalently, $T<em>C = T</em>K - 273.15.$
  • At the ice point, TK = 273.15 K; at the steam point, TK = 373.15 K.
• Relationship of gas properties to temperature:
  • For a fixed amount of an ideal gas at constant volume, the pressure is directly proportional to the absolute temperature: $$p
    ightarrow p ext{ increases as } T_K ext{ increases} \