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B.Sc Biochemistry Thermodynamics & Kinetic Theory — practice questions

Explore 15 free Thermodynamics & Kinetic Theory questions in B.Sc Biochemistry Chemistry. Open each question or exercise to read its content, reference answers and available explanation.

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Thermodynamics & Kinetic Theory questions and exercises with answers

Showing questions 1–15 of 15.

Which of the following is **not** a state function?Read the answer and worked solution →For an isothermal reversible expansion of an ideal gas from volume $V_1$ to $V_2$, the work done **by** the gas is:Read the answer and worked solution →When an ideal gas expands into a vacuum:Read the answer and worked solution →The relation between $\Delta H$ and $\Delta U$ for a reaction involving gases is:Read the answer and worked solution →The standard enthalpy of formation $\Delta_f H^\circ$ of any element in its most stable form at the standard state is:Read the answer and worked solution →The standard enthalpy of neutralisation of any strong acid by any strong base in dilute aqueous solution is approximately constant at:Read the answer and worked solution →Which of the following is **always** true for a spontaneous process in an isolated system?Read the answer and worked solution →At constant temperature and pressure, the criterion for a process to be **spontaneous** is:Read the answer and worked solution →A reaction is found to have $\Delta H = +30\,\text{kJ mol}^{-1}$ and $\Delta S = +100\,\text{J K}^{-1}\,\text{mol}^{-1}$ at $1\,\text{atm}$. The reaction is spontaneous when:Read the answer and worked solution →The relationship between $\Delta G^\circ$ and the equilibrium constant $K$ for a chemical reaction is:Read the answer and worked solution →Hess's law of constant heat summation is a direct consequence of:Read the answer and worked solution →For an adiabatic process, the first law of thermodynamics reduces to:Read the answer and worked solution →Knock out the false energy claimsRead the answer and worked solution →System or surroundings?Read the answer and worked solution →Which one does NOT belong?Read the answer and worked solution →

Worked practice questions

Which of the following is **not** a state function?

  1. Enthalpy $H$
  2. Work $W$
  3. Entropy $S$
  4. Internal energy $U$
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Correct answer: B. Work $W$

State functions depend only on the current state of the system, not on the path taken to reach it. Internal energy, enthalpy, entropy and Gibbs free energy are all state functions. Heat $q$ and work $W$ are path functions — their values depend on the process by which the change occurs.

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For an isothermal reversible expansion of an ideal gas from volume $V_1$ to $V_2$, the work done **by** the gas is:

  1. $-2.303\,nRT\,\log\dfrac{V_2}{V_1}$
  2. $+2.303\,nRT\,\log\dfrac{V_2}{V_1}$
  3. $0$
  4. $-p_\text{ext}(V_2 - V_1)$
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Correct answer: B. $+2.303\,nRT\,\log\dfrac{V_2}{V_1}$

For an isothermal reversible expansion, $W_\text{by gas} = +nRT\ln(V_2/V_1) = +2.303\,nRT\log(V_2/V_1)$. In the IUPAC convention $W_\text{on system} = -nRT\ln(V_2/V_1)$ is negative, but the question asks for work done *by* the gas, which is the positive of this.

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When an ideal gas expands into a vacuum:

  1. Internal energy decreases
  2. Heat absorbed is maximum
  3. Work done is zero because $p_\text{ext} = 0$
  4. Work done is maximum
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Correct answer: C. Work done is zero because $p_\text{ext} = 0$

$W = -p_\text{ext}\Delta V$. In a vacuum $p_\text{ext} = 0$, so $W = 0$ regardless of the volume change. For an ideal gas this also gives $q = 0$ (since $\Delta U = 0$ at constant temperature for an ideal gas) so the process is called *free expansion*. Both $q$ and $W$ being zero make $\Delta U = 0$ consistent with the isothermal condition.

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