310105g Heat and Temperature 2025 (TF)

HEAT AND TEMPERATURE

Objectives

• Describe the relationship between various temperature scales

• Describe temperature, heat, sources of heat energy, specific heat, and the laws of thermodynamics

• Describe molecular theory of heat and heat transfer, its significance on the change of state of a substance

• Explain coefficient of linear expansion, volumetric expansion, and surface expansion of liquids and solids

• Solve problems related to expansions of solids and liquids, and changes in heat content of liquids

• Describe laws related to heat, conductors, insulators and processes of heat transfer through conduction, convection, and radiation

• Understand steam tables and properties like sensible heat, latent heat of fusion, latent heat of evaporation, saturation temperature, and super heat

TEMPERATURE

Definition of Temperature

• Temperature is the measure of the movement (average kinetic energy) of molecules.

• Higher molecular movement (vibration) correlates with higher temperature.

TEMPERATURE SCALES

Key Temperature Scales

• Kelvin (K): Absolute zero is 0 K, where all molecular vibration stops.

  • Key Points:

    • H2O Freezes: 273 K

    • H2O Boils: 373 K

• Celsius (°C):

  • H2O Freezes: 0 °C

  • H2O Boils: 100 °C

• Fahrenheit (°F):

  • H2O Freezes: 32 °F

  • H2O Boils: 212 °F

• Conversion Processes:

  • °K = °C + 273

  • °C = (°F - 32) × 5/9

  • °F = (°C × 9/5) + 32

HEAT TRANSFER

Heat Transfer Mechanisms

1. Conduction: Transfer of heat through a solid.

2. Convection: Transfer through the movement of gas or liquid.

3. Radiation: Transfer of energy via photons in electromagnetic waves; can occur in a vacuum or transparent medium.

Heat Definition

• Heat is the transfer of energy from one object to another due to temperature differences.

HEAT

Definition

• Heat quantifies the transfer of energy; increases kinetic energy is measured as heating, while decreases are seen as loss of heat.

• Measured in Joules (Q).

SENSIBLE HEAT AND SPECIFIC HEAT

Sensible Heat

• Amount of energy required to raise temperature of a substance without changing its state.

• Formula: Q = mcΔT

  • Q = Heat energy (Joules)

  • m = mass (kg)

  • c = specific heat

  • ΔT = change in temperature (°C)

Specific Heat

• Energy needed to raise the temperature of a unit mass by one degree.

• Key properties are tabulated as Specific Heat Capacities.

THERMODYNAMICS

Laws of Thermodynamics

1. Energy cannot be created or destroyed, only transformed into other types.

   • Involves Internal energy, Kinetic energy, Potential energy.

2. Mechanical work derives from a body interacting with another at a lower temperature.

LATENT HEAT

Definition

• Amount of heat needed to change the state of a substance without varying its temperature.

  • Latent Heat of Fusion: Heat required to convert a solid into a liquid.

    • Formula: Q = mLf (Lf = 335 kJ/kg)

  • Latent Heat of Vaporization: Heat required to convert a liquid into vapor.

    • Formula: Q = mLv (Lv = 2256.6 kJ/kg)

THERMAL EXPANSION & CONTRACTION

Linear Expansion

• Heat typically makes substances expand; loss of heat leads to contraction.

• Coefficient of linear expansion varies by material.

• Formula: ΔL = α•Lo•ΔT

  • ΔL = change in length

  • α = linear expansion coefficient

  • Lo = initial length

  • ΔT = change in temperature

Area Expansion

• Heat causes the cross-sectional area to expand.

  • Formula: ΔA = y • Ao • ΔT (y = area coefficient of expansion).

Volume Expansion

• Heat results in an increase in volume, with the coefficient of volume expansion being three times the linear one.

  • Formula: ΔV = β•Vo•ΔT (β = volume coefficient of expansion).

Special Case: Water

• Water has its maximum density at 3.98 °C and expands upon freezing, causing potential pipe damage.

• Water vaporizes and expands 1700 times into steam.

ENERGY REQUIRED FOR PHASE CHANGE

Example Problem

• Converting a 10kg block of ice from -5 °C to steam at 105 °C.

1. Sensible heat from -5 °C to 0 °C

2. Latent heat of fusion at 0 °C

3. Sensible heat from 0 °C to 100 °C

4. Latent heat of vaporization at 100 °C

5. Sensible heat from 100 °C to 105 °C

Calculation Breakdown

• Total energy: Q = mcΔT + mLf + mcΔT + mLv + mcΔT.

TEST PREPARATION

Self-Test Coverage

• Include key concepts: Conduction, Convection, Radiation.