G11 Gen Thermal Energy Lesson 1 Mr. Adham Zewin (1)

Page 1: Heat and Thermal Energy Transfer

• Heat:

  • Definition: The transfer of thermal energy from a hotter object to a cooler one.

  • Direction: Heat flows spontaneously from hot to cold.

  • Conditions: Cannot flow cold to hot without work done.

  • Measurement: Measured in joules (J).

• Thermal Energy Transfer:

  • Occurs through contact and redistribution of energies via particle collisions.

  • Example: Heat transfers from warm skin to a cooler thermometer.

• Heat Absorption:

  • Positive heat value (Q) when an object absorbs thermal energy.

• Heat Loss:

  • Negative heat value (Q) when an object loses thermal energy.

• Types of Heat Transfer:

  • Conduction:

    • Description: Transfer through direct contact in solids.

    • Example: Metal rod heated at one end; spoon in hot water.

  • Convection:

    • Description: Transfer in liquids/gases through fluid motion.

    • Example: Water heating in a pot; atmospheric convection (e.g., thunderstorms).

  • Radiation:

    • Description: Energy transfer through electromagnetic waves, requiring no medium.

    • Example: Sun warming Earth; heat felt from fire or light bulb.

Page 2: Specific Heat

• Definition of Specific Heat:

  • The energy needed to raise the temperature of a unit mass of material by one degree.

  • Measurement: Joules per kilogram per degree Celsius (J/kg°C).

• Key Points:

  • Different materials heat at different rates; low specific heat materials heat faster (e.g., metals) while high specific heat materials heat slower (e.g., water).

  • Example: Aluminum specific heat = 900 J/kg°C (900 J required to raise 1 kg by 1°C).

• Specific Heat of Common Materials:

  • Metals: Low specific heat, good thermal conductors (used in cooking).

  • Water: High specific heat, heats slowly and retains heat longer.

  • Ice and Water Vapor: High specific heats.

• Real-World Implications:

  • Water’s high specific heat stabilizes large bodies of water and helps regulate body temperature.

Page 3: Measuring Heat

• Heat Measurement:

  • Formula: Q = mC∆T

  • Variables:

    • Q = heat

    • m = mass

    • C = specific heat of the substance

    • ∆T = change in temperature (final - initial)

• Example Calculation:

  1. Copper Water Pipe:

  • Mass = 2.3 kg, Initial Temperature = 20.0°C, Final Temperature = 80.0°C.

  • Q = (2.3 kg)(385 J/kg·K)(80.0°C - 20.0°C) = 5.3 × 10^6 J.

  2. Electric Heater Calculation:

  • Cost of heating 75 kg from 15°C to 43°C:

  • Q = (75 kg)(4180 J/kg·K)(43°C - 15°C) = 8.8 × 10^6 J.

  • Cost = (8.8 × 10^6 J)/(3.6 × 10^6 J/kWh) * $0.15/kWh = $0.37.

Page 4: Challenges in Heat Transfer

• Change in Temperature for Water:

  • Given 836.0 kJ added to 20.0 L water:

    • Q = mC∆T leads to ΔT = 10.0 K.

• Using Methanol:

  • Density = 0.80 g/cm³, mass of methanol = 16 kg:

    • Q = mC∆T results in ΔT = 21 K.

• Comparison of Coolants:

  • Water better than methanol for temperatures above 0°C due to less temperature change during thermal absorption.

Page 5: Calorimetry

• Calorimeter:

  • Device to measure thermal energy changes.

  • Insulated to minimize external energy transfer.

• Setup:

  • Hot substance and cold water reach equilibrium temperature.

• Working Principle:

  • Energy conservation in a closed system: energy can be transferred between substances without leaving the system.

Page 6: Energy Transfer Concept

• Energy Changes:

  • The energy change is equal to the heat transferred.

• Equilibrium Temperature:

  • Final temperature reached by both substances relates to their temperature changes.

• Specific Heat Calculation:

  • Positive energy change = rise in temperature; negative energy change = fall in temperature.

Page 7: Specific Heat Problems

• Aluminum Block in Water:

  • Aluminum (100g) at 100.0°C mixed with water (100g) at 10.0°C; final temperature = 26.0°C. Specific heat calculated using mC(Tf - Ti).

• Metal Weights Calculation:

  • Fishing weights (100g at 100°C) placed in water (100g at 35°C); final temperature = 45°C. Specific heat determined.

• Water Mixture Calculation:

  • Mixing 200g of water at 80°C with 200g of water at 10°C results in final temperature of 45°C.

Page 8: Challenge Problem on Mixing

• Water Mixed at Different Temperatures:

  • 400g water at 15°C mixed with 400g water at 85°C; the final equilibrium temperature calculated to be 50.0°C.

• Adding Methanol:

  • Addition of 400g methanol at 15°C to the previous mixture; equilibrium calculated to be 42.1°C.

Page 9: Energy Exchange During Collisions

• Collision Dynamics:

  • Objects absorb energy, exchange kinetic energy, or lose energy to the environment during collisions.

• Particle Energy in Gases:

  • Gases possess both linear and rotational kinetic energy.

• Potential Energy Causes:

  • Potential energy in materials results from internal bonds and particle interactions.

Page 10: Energy Transfer in Gases

• Energy Transfer Causes:

  • Caused by temperature gradients and collisions with container walls.

  • Uniform temperature distribution results from particle collisions.

Page 11: Kinetic Theory of Matter

• Kinetic Theory: Explains the relationship between random particle motion and macroscopic properties.

• Behavior of Helium Balloon:

  • Expands in sunlight due to increased speed and frequency of collisions of helium atoms.

Page 12: Thermal Energy in Solids

• Solids' Atomic Behavior:

  • Atoms in solids vibrate in place but do not move.

• Absolute Zero:

  • Atoms become motionless when cooled to absolute zero, considered the lowest possible temperature.

Page 13: Temperature Dependence

• Temperature Definition: Depends on the average kinetic energy of particles, independent of the total number of particles.

• Thermal Energy: Depends on both temperature and number of particles; larger objects at the same temperature have more thermal energy.

Page 14: Measuring Temperature with Thermometers

• Thermometer Function: Thermal energy transfer occurs when placed in contact with bodies, leading to temperature equilibrium.

• Kinetic Energy Comparison: Particle kinetic energy varies between thermometer and body.

Page 15: Thermal Conduction Overview

• Thermal Conduction Defined: Transfer of thermal energy through particle collisions, especially in solids.

• Skin and Thermometer Interaction: Thermal energy transfers from skin to thermometer upon contact.

Page 16: Thermal Equilibrium Explained

• Equilibrium: Occurs when the thermometer and body reach the same temperature; energy transfer stops.

• Energy Distribution: Systems naturally move towards uniform energy distribution.

Page 17: Temperature Limits and Absolute Zero

• Upper Temperature Limit: No known maximum but absolute zero indicates the minimal kinetic energy scenario.

• Significance of Absolute Zero: Atoms lose all thermal energy and kinetic energy, marking it as the lowest temperature.

Page 18: Heat Definitions and Measurements

• Heat Definition: The transfer of thermal energy from hotter to cooler regions.

• Heat Flow Direction: Naturally from hot to cold.

• SI Unit: Joule (J).

• Positive Heat Absorption: Indicates a gain in thermal energy.

• Example of Conduction: A spoon heating in coffee.

Page 19: Heat Transfer Processes

• Convection: Heat transfer through fluid movement.

• Radiation: Heat transfer through electromagnetic waves.

• Thermal Equilibrium: The state where heat transfer ceases between bodies.

• Metal Thermal Conductivity: Metals feel colder due to their rapid heat conduction compared to wood.

Page 20: Understanding Specific Heat

• Specific Heat Definition: Energy required to raise the temperature of a unit mass by 1°C.

• Water's Heating Characteristics: Takes longer to heat due to higher specific heat than metals.

• Heat Transfer Examples: The warmth from a bonfire is attributed to radiation.