Physics Chapter 19: Heat and Thermodynamics

Chapter 19: Heat and the First Law of Thermodynamics

• Heat as Energy Transfer: Heat is a form of energy that flows from one object to another due to a temperature difference. The unit of heat is the calorie (cal), where 1 cal is the amount of heat needed to raise the temperature of 1 gram of water by 1°C. 4.186 J equals 1 cal and 4.186 kJ equals 1 kcal.

Heat as Energy Transfer - Definitions

• Definition of Heat: Heat is energy transferred from one object to another because of a difference in temperature.

• Temperature: A measure of the average kinetic energy of the molecules in an object. An increase in temperature signifies increased molecular kinetic energy. The relationship between these is: kT = (1/3) K, where k is Boltzmann's constant

• Internal Energy: The sum of all energy of the molecules in an object, encompassing kinetic and potential energy. Internal energy is related to temperature; higher temperature leads to higher internal energy.

Internal Energy

• Monatomic Ideal Gas: For a monatomic (single-atom) ideal gas, internal energy is given as Eint = (3/2)NkT, where N is the number of molecules, k is Boltzmann's constant, and T is the temperature.

• Gas Molecules with Multiple Atoms: Gas molecules with multiple atoms additionally possess rotational and vibrational energy, increasing their internal energy compared to monatomic gases.

Specific Heat

• Specific Heat (c): The amount of heat required to raise the temperature of 1 kg of a substance by 1°C. The value of 'c' depends on the material. Q = mc∆T. This is a constant of proportionality.

• Table of Specific Heats: A table (Table 19-1) provides specific heat values for various substances, including Aluminum, Ethyl Alcohol, Copper, Glass, Iron, Steel, Lead, Marble, Mercury, Silver, Wood, Water, Ice (-5°C & 15°C), and Steam (110°C). Also listed are values for Human body (average) and Protein.

Calorimetry

• Closed System: A system that neither gains nor loses mass during a process, but can exchange energy with the environment.

• Open System: A system that can exchange both mass and energy with its surroundings.

• Isolated System: A system that neither exchanges mass nor energy with its surroundings.

• Calorimetry Principle: In an isolated system, heat lost by one object equals heat gained by another.

Latent Heat (19.5)

• Latent Heat: Heat required to change the state of a substance without changing its temperature.

• Smeltwarmte (LF): Heat to change a substance from solid to liquid.

• Verdampingswarmte (LV): Heat needed to change a substance from liquid to gas (vapor).

• Total Heat (Q): Total heat for a phase change is directly proportional to the mass and latent heat(Q=mL)

• Example application (19.5): Calculating temperature changes when ice is added to warmer liquid, considering latent heat for the phase change.

First Law of Thermodynamics

• Statement of the First Law: The change in internal energy of a closed system is equal to the heat absorbed minus the work done by the system on its surroundings. ∆Eint = Q - W.

• Work Calculation: Work done by a system undergoing an infinitesimal volume change: dW = F.dl = P.dV The total work done during a finite volume change is calculated by integrating this relationship across the volume change. 'W' = ∫dW

• Isothermal Processes: Processes with constant temperature.

• Adiabatic Processes: Processes with no heat exchange with the environment (Q=0).

Molaire soortelijke warmtes (19.8)

• Gas Specific Heat Dependence: The specific heat of a gas depends on the process (isobaric or isovolumetric) occurring within it.

• Molar Specific Heat for Gases: Molar specific heat (Cp and Cv) are used for gases.

• Calculation of the specific heat: There are formulas for calculating the specific heat (Qv and Qp).

• Equipartition Theorem: The total internal energy of a gas is equally divided among its active degrees of freedom, each degree contributing 1/2 kT to the total internal energy.

Adiabatic Expansion (19.9)

• Adiabatic Expansion Equation: Combining the ideal gas law with the definition for internal energy change and adiabatic conditions produces an equation for how pressure and volume are related through the process. (PV^y = constant)

Heat Transfer Mechanisms(19.10)

• Conduction: Heat transfer through material by molecular collisions. Equation for the heat transfer rate between two objects of different temperatures (ΔQ/Δt = kA(T1 − T2)/l) where k is thermal conductivity.

• Convection: Heat transfer due to bulk motion of fluid (liquid or gas).

• Radiation: Heat transfer through electromagnetic waves.

• Emissivity: A factor that measures how effectively a surface emits thermal radiation. It ranges between 0 and 1; black bodies (perfect emitters) have emissivity of 1 and white bodies (non-emitters) have emissivity of 0. The rate of energy transfer is determined by the emissivity, area (of both objects), and their temperature difference.

• Other Considerations: Calculations for heat transfer from the sun account for the angle of incidence of solar radiation, which influences the energy absorbed by the surface.

Explore the key concepts of heat transfer and the first law of thermodynamics in this quiz based on Chapter 19. Understand the definitions of heat, temperature, and internal energy, and how they relate to energy transfer processes. Perfect for reinforcing your knowledge in physics!