المحاضرة 7: كمية الحرارة

Lecture 7: Quantity of Heat

• The lecture is about the quantity of heat.
• Heat energy (Q) is defined as the transfer of thermal energy.
• Q = mcΔT (One phase: solid, liquid, or gas)
  • m = mass of the substance
  • c = specific heat capacity
  • ΔT = change in temperature
• Q = mL (Phase change)
  • L = latent heat
• c: specific heat capacity.
  • SI unit: J/kg K
  • British unit: Btu/lb °F
• L_f: latent heat of fusion.
  • SI unit: J/kg
  • British unit: Btu/lb
• L_v: latent heat of vaporization.
  • SI unit: J/kg
  • British unit: Btu/lb
• Q = mL_f (Melting)
  • m = mass of the substance that melted.
• Q = mL_v (Vaporization)
  • m = mass of the substance that vaporized.
• Q (lost) = Q (gained) - The law of conservation of energy applies.

Specific Heat (c) & Latent Heat (L)

• c = Q / mΔT
  • Amount of heat needed to raise the temperature of a unit mass of a substance by 1°C
• L = Q / m
  • Amount of heat needed to change the phase of a unit mass of a substance without changing the temperature.
• Substances with higher specific heat capacity take longer to warm or cool.
• Substances with lower specific heat capacity take shorter time to warm or cool.

Specific Heat (c) of Substances

• Charts showing the specific heat capacity (c) of various substances (e.g., aluminum, silver, brass, etc.) are presented in tables. Values in J/kg °C are included.

Phase Change

• Melting, freezing, vaporization, and condensation are phase changes.
• L_f = Latent heat of fusion (melting) = Latent heat of freezing
• L_v = Latent heat of vaporization = latent heat of condensation
• At melting and boiling points, phase changes occur at constant temperature.

Latent Heat of Fusion and Vaporization of Substances

• Data tables present the latent heat of fusion (L_f) and latent heat of vaporization (L_v) for substances like Helium, Nitrogen, Oxygen, Ethyl alcohol, Water, Sulfur, Lead, Aluminum, Silver, Gold, and Copper. Units given include °C and J/kg.

Heating Curve of Water

• Water illustrates phase changes due to heat addition.
• Q = mc ΔT (No phase change)
• Q = mL (Phase change, constant temperature)

Example/Equations

• The lecture presents equations and examples regarding the calculation of heat transfer and phase changes involving ice, water and steam.
• Q = Q₁ + Q₂ + Q₃ + Q₄ + Q₅
• Examples with relevant parameters (e.g. mass, Specific heat capacities, Latent heats)

Important Concepts (Summary)

• Absolute zero (0 K): Temperature at which molecular movement stops.
• Melting point: Solid to liquid phase change temperature.
• Freezing point: Liquid to solid phase change temperature.
• Boiling point: Liquid to gas phase change temperature.
• Condensation point: Gas to liquid phase change temperature.

The Law of Conservation of Energy

• Energy can't be created or destroyed, only transformed.
• Q_lost = Q_gained

Examples and Problems

• Worked examples presented include calculating mass of steam needed to raise temperature of water in a glass container.

Multiple Choice Questions (MCQ)

• Multiple choice questions are about concepts like freezing/solidifying, the unit for latent heat, amount of energy needed to change phase, and specific heat capacity.
• SI units for specific heat are given in the MCQ.

تتناول هذه المحاضرة كمية الحرارة وكيفية حسابها باستخدام المعادلات الأساسية. سيتم استكشاف مفهوم الطاقة الحرارية وتغيرات الطور، بالإضافة إلى الحرارة النوعية والحرارة الكامنة. تعلم القوانين المرتبطة بحفظ الطاقة وتأثيرها على المادة.