Questions and Answers
What is the sum of the changes in internal, kinetic, and potential energies equal to?
What is the unit of energy in the first law of thermodynamics written on a unit-mass basis?
What is the difference between heat transfer and work from the first law point of view?
What is the energy stored in chemical bonds called?
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What is the energy associated with the motion of an object?
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What is the law of energy conservation also known as?
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What is the first law of thermodynamics based on?
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What is the sign convention for heat transfer in a system?
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What is the unit of heat transfer rate?
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What is heat defined as, based on kinetic theory?
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What do both work and heat transfer have in common?
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What is the first law of thermodynamics also known as?
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What is the fundamental principle of physics stated by the Law of Conservation of Energy?
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What was the main purpose of Joule's experiment?
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What is the relationship between heat and work?
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What is internal energy (U) in a thermodynamic system?
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What is the equation for the work done on a system?
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What is the significance of the equation dU = dQ - P dV?
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What is the primary factor that internal energy is a function of in ideal gases?
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What is the definition of enthalpy?
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What is the relationship between the specific heat at constant volume and the specific heat at constant pressure?
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What is the change in enthalpy equal to in a constant pressure process?
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What is the internal energy of a system a function of in non-ideal gases and other systems?
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What is Cv related to in a thermodynamic system?
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What is the relationship between specific heat at constant volume and specific heat at constant pressure for an ideal gas?
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What is the characteristic of a reversible adiabatic process?
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What is the condition for an ideal gas to follow the equation h = h(T)?
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What is the definition of enthalpy for an ideal gas?
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What is the characteristic of a constant volume process?
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What is the equation for the change in internal energy of an ideal gas in a constant volume process?
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What is the method of heat transfer involving the movement of fluids?
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What is the change in internal energy of a system represented by?
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What is the work done on a system during compression of a gas equal to?
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What is the energy transferred through a force applied over a distance?
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What is the process called when a gas is compressed or expanded in a cylinder while maintaining a constant temperature?
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What is the change in internal energy of a system due to heat transfer and work done?
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What is the work done by a gas during expansion equal to?
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What is the force applied to lift a weight against gravity?
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What is the unit of internal energy typically measured in?
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What is the process called when a gas is compressed or expanded in a cylinder without any heat transfer?
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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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Description
This quiz covers the basics of the First Law of Thermodynamics, including energy exchange between systems and surroundings through heat and work transfer.