Thermodynamics First Law Quiz
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Questions and Answers

What does the change in enthalpy (ΔH) represent during a process at constant pressure?

  • The heat absorbed or released by the system (correct)
  • The total energy change of the system including work done
  • The change in the internal energy of the system
  • The change in temperature of the system

    • In thermochemistry, which of the following is true for an endothermic process?

  • The external pressure must increase
  • Heat is gained by the system (ΔH > 0) (correct)
  • The process occurs spontaneously without energy input
  • Heat is released from the system (ΔH < 0)

    • Which statement best describes the significance of enthalpy in pharmaceutical applications?

  • It relates to the viscosity of liquid medications
  • It is essential for predicting drug solubility and stability (correct)
  • It helps determine the molecular weight of drug compounds
  • It is used to calculate the pH of drug solutions

    • When calculating the enthalpy change for a reaction, which enthalpy of formation value is often considered zero?

    <p>ΔHf ⁰ O2 (g)</p> Signup and view all the answers

    Which formula correctly represents the relationship between internal energy (U) and enthalpy (H)?

    <p>H = U + PV</p> Signup and view all the answers

    What does the First Law of Thermodynamics state?

    <p>Energy can neither be created nor destroyed.</p> Signup and view all the answers

    In the context of ideal gases, which of the following statements about internal energy is correct?

    <p>Internal energy depends solely on molecular motion and energy storage.</p> Signup and view all the answers

    What happens to the internal energy of an isolated system?

    <p>It remains constant despite energy transformations.</p> Signup and view all the answers

    When discussing changes to internal energy (ΔU), what does a positive ΔU indicate?

    <p>Energy flows into the system, increasing its energy.</p> Signup and view all the answers

    Which type of energy is NOT considered a part of internal energy (U) for a system of ideal gases?

    <p>Potential energy from molecular interactions.</p> Signup and view all the answers

    Which statement best describes the relationship between the internal energy of a system and its surroundings according to the First Law of Thermodynamics?

    <p>Any change in the system's internal energy is compensated by an opposite change in the surroundings.</p> Signup and view all the answers

    What types of energy contribute to the internal energy (U) of a system composed of particles?

    <p>Translational, rotational, vibrational, and electronic energy storage.</p> Signup and view all the answers

    Which of the following best illustrates the concept of energy transformation in an isolated system?

    <p>Energy changes form between translational and vibrational energy, but total energy remains constant.</p> Signup and view all the answers

    In the context of gas expansion, how is work defined?

    <p>As the product of pressure and the small change in volume</p> Signup and view all the answers

    What sign convention is used to represent work done by an expanding gas?

    <p>Work is negative because the system's energy is used up</p> Signup and view all the answers

    To calculate total work done over a finite volume change at constant pressure, what mathematical operation is required?

    <p>Integrate small work increments over the volume range</p> Signup and view all the answers

    What happens to the internal energy of a gas when work is done on it during compression?

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

    Which thermodynamic process maintains constant pressure while allowing volume changes?

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

    During the expansion of an ideal gas in a cylinder, what is assumed about the pressure throughout the expansion?

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

    If a gas undergoes expansion from an initial volume Vi to a final volume Vf, what role does pressure play in the work calculation?

    <p>It can be taken outside the integral due to being constant</p> Signup and view all the answers

    What best describes the equilibrium condition during gas expansion?

    <p>The gas reaches equilibrium after each infinitesimal change in volume</p> Signup and view all the answers

    In thermodynamics, what does the term 'PdV' represent in the context of work done?

    <p>The pressure multiplied by the change in volume during a process</p> Signup and view all the answers

    What happens to the internal energy of a system when it performs work on its surroundings?

    <p>The internal energy decreases.</p> Signup and view all the answers

    If a system absorbs heat from its surroundings, what is the sign of q, the heat transfer?

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

    What is a defining characteristic of adiabatic processes in thermodynamics?

    <p>No heat exchange occurs with the surroundings</p> Signup and view all the answers

    Which statement regarding work done on a system is correct?

    <p>Work done on the system increases its internal energy.</p> Signup and view all the answers

    In the context of the First Law of Thermodynamics, which of the following correctly describes the relationship of heat (q) and work (w) for a closed system?

    <p>ΔU = q + w</p> Signup and view all the answers

    What is the effect on internal energy when a system loses heat to its surroundings?

    <p>Internal energy decreases.</p> Signup and view all the answers

    What happens to the internal energy of a gas when it expands against a piston?

    <p>It decreases.</p> Signup and view all the answers

    Which of the following describes the relationship between pressure (P), volume (V), and work (w) done by a gas?

    <p>w = -P * dV</p> Signup and view all the answers

    How is the internal energy of a system affected if it undergoes a phase change?

    <p>It can either increase or decrease depending on the phase change.</p> Signup and view all the answers

    If a system is at constant pressure and undergoes a small increase in volume, what can be inferred about the work done?

    <p>Work is positive.</p> Signup and view all the answers

    If a system performs work on its environment and simultaneously loses heat, which statement is true about its internal energy?

    <p>It decreases due to work and heat loss.</p> Signup and view all the answers

    What happens to the internal energy ΔU during a constant volume process?

    <p>It is determined only by heat exchange with surroundings.</p> Signup and view all the answers

    Which equation correctly represents the work done by a gas during expansion at constant pressure?

    <p>w = -P(Vf − Vi)</p> Signup and view all the answers

    In a constant pressure process, which component contributes to the change in internal energy ΔU?

    <p>Heat transferred and work done due to volume change.</p> Signup and view all the answers

    What does the symbol qp represent in thermodynamics?

    <p>Heat transferred at constant pressure.</p> Signup and view all the answers

    Enthalpy (H) combines which two thermodynamic quantities?

    <p>Internal energy and pressure-volume product.</p> Signup and view all the answers

    Which condition must hold true for work to be done by the system in a thermodynamic process?

    <p>The volume must change (ΔV ≠ 0).</p> Signup and view all the answers

    When considering pharmaceutical processes, why is understanding constant pressure conditions crucial?

    <p>They allow for precise measurement of heat changes.</p> Signup and view all the answers

    What is the principal outcome of energy transfer in a constant volume process?

    <p>Energy transfer occurs only through heat exchange.</p> Signup and view all the answers

    Which statement regarding enthalpy change (ΔH) at constant pressure is correct?

    <p>ΔH equals the heat exchanged under constant pressure conditions.</p> Signup and view all the answers

    If the volume does not change during a thermodynamic process, what can be concluded about the work done by the system?

    <p>The work done is zero.</p> Signup and view all the answers

    Study Notes

    First Law of Thermodynamics

    • Energy cannot be created or destroyed, it can only be transformed from one form to another
    • Internal energy (U) is total energy within a system, including translational, rotational, vibrational, and electronic energy
    • In an isolated system, internal energy is constant
    • Changes in internal energy (ΔU) can occur through heat transfer or work done
    • Heat (q) is energy transferred due to temperature difference
    • Work (w) is energy transferred as force applied over a distance
    • ΔU = q + w
    • Work done by a gas at constant pressure can be expressed as w = -PΔV

    Constant Volume and Constant Pressure Processes

    • In a constant volume process (ΔV = 0), there is no work done (w = 0)
    • Changes in internal energy are solely due to heat exchange (ΔU = qv)
    • In a constant pressure process, changes in internal energy are affected by both heat transfer (qp) and work done (PΔV): ΔU = qp + PΔV
    • Enthalpy change (ΔH) is defined as ΔH = ΔU + PΔV, and at constant pressure, ΔH = qp

    Enthalpy (H)

    • Enthalpy is a thermodynamic quantity that provides insight into the heat content of a system at constant pressure
    • H = U + PV
    • Enthalpy change (ΔH) represents the heat absorbed or released by the system at constant pressure

    Thermochemistry

    • Branch of chemistry dealing with heat changes during chemical reactions
    • Enthalpy Change (ΔH): heat absorbed or released at constant pressure
    • Endothermic Process: heat absorbed by the system (ΔH > 0)
    • Exothermic Process: heat released by the system (ΔH < 0)
    • Standard enthalpy change (ΔH°) is the enthalpy change for a reaction under standard conditions (298 K and 1 atm)
    • Hess's Law: Enthalpy change for a reaction can be calculated by adding the enthalpy changes of a series of reactions that add up to the overall reaction

    Calculating Enthalpy Changes

    • Standard enthalpy of formation (ΔHf°) is the enthalpy change when one mole of a compound is formed from its elements in their standard states
    • ΔH°reaction = ΣnΔHf°(products) - ΣmΔHf°(reactants)
    • Where n and m are the stoichiometric coefficients of the products and reactants, respectively

    Example of Calculating Enthalpy Change

    • The enthalpy change for the combustion of one mole of glucose can be calculated using the standard enthalpy of formation values for glucose, oxygen, carbon dioxide, and water
    • The balanced equation for the reaction is: C6H12O6(s) + 6O2(g) -> 6CO2(g) + 6H2O(l)
    • ΔH°reaction = [6ΔHf°(CO2) + 6ΔHf°(H2O)] - [ΔHf°(C6H12O6) + 6ΔHf°(O2)]
    • Substituting the values given in the text: ΔH°reaction = [(6 x -393.5) + (6 x -285.8)] - [-1273.0 + (6 x 0)] = -2803.0 kJ/mol
    • This result indicates that the combustion of glucose is an exothermic reaction, releasing 2803.0 kJ of heat per mole of glucose burned.

    Applications of Thermodynamics in Pharmaceuticals

    • Understanding energy changes in drug formulation, interactions, and stability
    • Predicting how substances interact and change under different conditions
    • Optimizing drug delivery and manufacturing processes
    • Developing new drugs and therapies based on thermodynamic principles

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    First Law of Thermodynamics PDF

    Description

    Test your understanding of the First Law of Thermodynamics, including concepts of internal energy, heat transfer, and work done. This quiz also covers constant volume and constant pressure processes, as well as the relationship between internal energy and enthalpy changes.

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