First Law of Thermodynamics
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Questions and Answers

What is the fundamental principle of the First Law of Thermodynamics?

  • Energy can only be created, but not destroyed or changed.
  • Energy can be neither created nor destroyed, it can only change forms. (correct)
  • Energy can only be destroyed, but not created or changed.
  • Energy can be created or destroyed, but not changed.

    • What are the forms of energy transfer across the system boundary?

  • Heat, electricity, and magnetism
  • Work, heat, and sound
  • Work and heat (correct)
  • Heat, work, and electricity

    • What is the definition of heat based on kinetic theory?

  • The energy associated with the vibrating atoms and molecules.
  • The energy associated with the random motions of atoms and molecules. (correct)
  • The energy associated with the stationary atoms and molecules.
  • The energy associated with the orderly motions of atoms and molecules.

    • What is the sign convention for heat transfer?

    <p>Heat transfer to a system is positive, and heat transfer from a system is negative.</p> Signup and view all the answers

    What is the characteristic of heat and work?

    <p>Both are path functions.</p> Signup and view all the answers

    Why is the First Law of Thermodynamics considered a fundamental principle?

    <p>It is based on experimental observations.</p> Signup and view all the answers

    What is the fundamental principle of physics implied by the law of conservation of energy?

    <p>Energy cannot be created or destroyed, only converted or transferred.</p> Signup and view all the answers

    What was the primary objective of Joule's experiment?

    <p>To demonstrate the conversion of mechanical work into heat.</p> Signup and view all the answers

    What is the term for the energy of motion of particles in a thermodynamic system?

    <p>Thermal energy</p> Signup and view all the answers

    What is the mathematical expression for the work done on a system?

    <p>W = F dx</p> Signup and view all the answers

    What is the condition for a process to be considered quasi-static?

    <p>The process is slow and reversible.</p> Signup and view all the answers

    What is the implication of the equation ?dU = 0?

    <p>Energy is a state function, depending only on the current state of the system.</p> Signup and view all the answers

    What is the change in total energy of a system during a process expressed as?

    <p>The sum of the changes in its internal, kinetic, and potential energies</p> Signup and view all the answers

    What is the first law of thermodynamics for a cyclic process?

    <p>Q - W = 0</p> Signup and view all the answers

    What is the energy associated with the motion of an object?

    <p>Kinetic energy</p> Signup and view all the answers

    What is the energy stored in chemical bonds?

    <p>Chemical energy</p> Signup and view all the answers

    What is the transfer of energy when a force is applied over a distance or when a system changes its volume under pressure?

    <p>Work</p> Signup and view all the answers

    What is the energy balance for a closed system?

    <p>The total energy remains constant</p> Signup and view all the answers

    What is the relationship between internal energy and temperature for an ideal gas?

    <p>u = u(T)</p> Signup and view all the answers

    What is the specific heat ratio for monatomic gases?

    <p>1.67</p> Signup and view all the answers

    What is the assumption made for solids and liquids in thermodynamics?

    <p>Incompressible</p> Signup and view all the answers

    What is the equation for the change in internal energy of an incompressible substance?

    <p>?U = mCv(T2-T1)</p> Signup and view all the answers

    What is the process equation for a reversible polytropic process?

    <p>pVn = C</p> Signup and view all the answers

    What is the First Law of Thermodynamics for a closed system?

    <p>?U = Q - W</p> Signup and view all the answers

    What is the primary function of internal energy in thermodynamics?

    <p>To represent the total energy contained within a system</p> Signup and view all the answers

    What is the relationship between internal energy and temperature in an ideal gas?

    <p>Internal energy is a function of temperature only</p> Signup and view all the answers

    What is enthalpy in thermodynamics?

    <p>The total energy of a system plus the energy associated with the pressure and volume</p> Signup and view all the answers

    What is the difference between specific heat at constant volume and specific heat at constant pressure?

    <p>Cp is always higher than Cv</p> Signup and view all the answers

    What is the correct expression for the change in internal energy at constant volume?

    <p>dU = nCvdT</p> Signup and view all the answers

    What is the relationship between Cv and Cp?

    <p>Cv is related to the changes in internal energy, and Cp to the changes in enthalpy</p> Signup and view all the answers

    What is the primary method of energy transfer in a closed system?

    <p>Heat transfer</p> Signup and view all the answers

    In a non-flow process, what is the effect of compression on the internal energy of a gas?

    <p>It increases the internal energy</p> Signup and view all the answers

    What is the mathematical expression for the work done during the compression of a gas?

    <p>W = -PdV</p> Signup and view all the answers

    Which of the following processes involves no heat transfer?

    <p>Adiabatic process</p> Signup and view all the answers

    What is the unit of internal energy?

    <p>Joules (J)</p> Signup and view all the answers

    What is the effect of an isothermal expansion on the internal energy of a system?

    <p>It remains constant</p> Signup and view all the answers

    Which of the following is an example of work done by the system?

    <p>Expansion of a gas</p> Signup and view all the answers

    What is the mathematical expression for the work done during the lifting of a weight?

    <p>W = mgh</p> Signup and view all the answers

    What is the change in internal energy of a system during an isothermal process?

    <p>∆U = 0</p> Signup and view all the answers

    What is the relationship between work done and internal energy in a closed system?

    <p>∆U = -W</p> Signup and view all the answers

    Study Notes

    First Law of Thermodynamics

    • The first law of thermodynamics states that energy cannot be created or destroyed, only converted from one form to another.
    • The law can be mathematically expressed as: Q - W = ΔE (energy transferred as heat minus energy transferred as work equals the change in internal energy)
    • The law is based on experimental observations and cannot be proved mathematically.

    Energy Transfer Mechanisms

    • Heat (Q): energy transferred due to a temperature difference between the system and its surroundings.
    • Work (W): energy transferred when a force is applied over a distance or when a system changes its volume under pressure.

    Energy Conservation in a Closed System

    • For a closed system, the total energy (kinetic, potential, and internal energies) remains constant, although it can change forms.
    • The energy balance needs to account for the energy carried by the mass entering and leaving the system.

    Law of Conservation of Energy

    • The law of conservation of energy states that the total energy in an isolated system remains constant over time, although energy can transform from one form to another.
    • This fundamental principle of physics implies that energy cannot be created or destroyed, only converted or transferred.

    Joule's Experiment

    • James Prescott Joule's experiment demonstrated the mechanical equivalent of heat.
    • The experiment showed that mechanical work could be converted into heat, providing strong evidence for the conservation of energy.

    Energy as a Property of a System

    • Energy is a property of a thermodynamic system, meaning it is a state function that describes the energy content of the system.
    • Energy is a scalar quantity that encompasses various forms, including kinetic, potential, internal, thermal, chemical, electrical, nuclear, and radiant energy.

    Internal Energy

    • Internal energy (U) is a fundamental concept in thermodynamics that represents the total energy contained within a system.
    • Internal energy is a state function that depends on the temperature of the system.
    • For an ideal gas, internal energy (U) is a function of temperature (T) only.

    Enthalpy

    • Enthalpy (H) is a thermodynamic property that represents the total energy of a system.
    • Enthalpy is defined as: H = U + PV, where U is the internal energy, P is the pressure, and V is the volume.
    • Enthalpy is a useful concept for analyzing thermodynamic systems, especially in chemical engineering and chemistry.

    Specific Heats

    • The specific heat is defined as the energy required to raise the temperature of a unit mass of a substance by one degree.
    • There are two kinds of specific heats: specific heat at constant volume (Cv) and specific heat at constant pressure (Cp).
    • Cp is always higher than Cv because at constant pressure the system is allowed to expand and energy for this expansion must also be supplied to the system.

    First Law of Thermodynamics for Non-Flow Processes

    • The First Law of Thermodynamics can be applied to non-flow processes, also known as closed systems or batch processes.
    • The First Law for a closed system is: ΔE = Q - W, where ΔE is the change in internal energy, Q is the heat added to the system, and W is the work done on the system.

    Examples of Non-Flow Processes

    • Heating a solid: heat is added, and the internal energy increases.
    • Compression of a gas: work is done on the system, and the internal energy increases.
    • Phase change: heat is added, and the internal energy increases.
    • Expansion of a gas: work is done by the system, and the internal energy decreases.
    • Cooling a solid: heat is removed, and the internal energy decreases.

    Isothermal and Adiabatic Processes

    • Isothermal process: a process in which the temperature remains constant, and no heat is added or removed.
    • Adiabatic process: a process in which there is no heat transfer between the system and the surroundings, and the internal energy changes due to work done on or by the system.### Work Done in Different Scenarios

    Work Done in Compressing a Gas

    • Work done on the system: W = -PdV (negative sign indicates work done on the system)
    • Force applied by piston: F = PA (where P is pressure and A is area)
    • Displacement of piston: dx = dV/A (where dV is change in volume)
    • Work done: W = Fdx = PAdx = PdV

    Work Done in Expanding a Gas

    • Work done by the system: W = PdV (positive sign indicates work done by the system)
    • Force applied by gas: F = PA
    • Displacement of piston: dx = dV/A
    • Work done: W = Fdx = PAdx = PdV

    Work Done in Lifting a Weight

    • Work done by force applied to lift weight against gravity: W = mgh (where m is mass, g is acceleration due to gravity, and h is height lifted)
    • Force lifting weight: F = mg
    • Displacement of weight: h (height lifted)
    • Work done: W = Fdh = mgh

    Work Done in Stirring or Agitation

    • Work done by stirrer or agitator: W = τθ (where τ is torque and θ is angular displacement)
    • Torque applied: τ
    • Angular displacement: θ
    • Work done: W = τdθ = τθ

    Work Done in Isothermal and Adiabatic Processes

    • Isothermal compression or expansion: W = 0 (no work is done since process occurs at constant temperature and pressure)
    • Adiabatic compression: W = -PdV (compression)
    • Adiabatic expansion: W = PdV (expansion)
    • Sign convention for work done:
      • Negative sign (-) indicates work done on the system
      • Positive sign (+) indicates work done by the system

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    Learn about the fundamental principle of thermodynamics, including energy transfer between systems and surroundings through heat and work.

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