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Chemistry · THERMODYNAMICS
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Chemistry · THERMODYNAMICS
Which of the following substances has a standard molar enthalpy of formation (\( \Delta_f H^\ominus \)) equal to zero at 298 K and 1 bar by convention?
Read answer →Chemistry · THERMODYNAMICS
For the reaction \( 4\text{Fe}(s) + 3\text{O}_2(g) \rightarrow 2\text{Fe}_2\text{O}_3(s) \) at \( 298\text{ K} \), \( \Delta_r H^\circ = -1648\text{ kJ mol}^{-1} \) and \( \Delta_r S^\circ = -549.4\text{ J K}^{-1}\text{mol}^{-1} \). What is the total entropy change \( \Delta S_{\text{total}} \)?
Read answer →Chemistry · THERMODYNAMICS
2.0 moles of liquid water at \( 100^\circ\text{C} \) is completely converted to ice at \( 0^\circ\text{C} \) at 1 bar pressure. Given that the heat capacity of liquid water is \( 4.2\text{ J g}^{-1\,\circ}\text{C}^{-1} \) and the enthalpy of fusion of ice is \( 6.00\text{ kJ mol}^{-1} \), the total enthalpy change (\( \Delta H \)) for this process is:
Read answer →Chemistry · THERMODYNAMICS
Refer to the given figure showing three types of thermodynamic systems (a), (b), and (c). Which of the following statements correctly identifies the boundaries and exchanges?
Read answer →Chemistry · THERMODYNAMICS
For the formation reaction \( \text{H}_2(g) + \text{Br}_2(l) \to 2\text{HBr}(g) \), the reaction enthalpy is \( \Delta_r H^\ominus = -72.8\text{ kJ mol}^{-1} \). What is the standard molar enthalpy of formation (\( \Delta_f H^\ominus \)) of \( \text{HBr}(g) \)?
Read answer →Chemistry · THERMODYNAMICS
Consider the following chemical reactions and statements regarding \( \Delta H \) and \( \Delta U \) at constant temperature: (A) For the reaction \( \text{C}(s) + \text{O}_2(g) \rightarrow \text{CO}_2(g) \), \( \Delta n_g = 0 \), therefore \( \Delta H = \Delta U \). (B) For the reaction \( \text{N}_2(g) + 3\text{H}_2(g) \rightarrow 2\text{NH}_3(g) \), \( \Delta n_g = -2 \), therefore \( \Delta H < \Delta U \). (C) For the reaction \( \text{PCl}_5(g) \rightarrow \text{PCl}_3(g) + \text{Cl}_2(g) \), \( \Delta n_g = +1 \), therefore \( \Delta H > \Delta U \). (D) For an isochoric process with no non-expansion work, \( \Delta U = q_v \). How many of the above statements are correct?
Read answer →Chemistry · THERMODYNAMICS
For the reaction \( \text{Fe}_2\text{O}_3(s) + 3\text{H}_2(g) \rightarrow 2\text{Fe}(s) + 3\text{H}_2\text{O}(l) \), the standard enthalpy change is \( \Delta_r H_1^\ominus = -33.3\text{ kJ mol}^{-1} \). What is the standard enthalpy change \( \Delta_r H_2^\ominus \) for the reaction: \( \frac{1}{2}\text{Fe}_2\text{O}_3(s) + \frac{3}{2}\text{H}_2(g) \rightarrow \text{Fe}(s) + \frac{3}{2}\text{H}_2\text{O}(l) \)?
Read answer →Chemistry · THERMODYNAMICS
Starting from the Gibbs function \( G = H - TS \), which differential relation holds true for a finite change at constant temperature?
Read answer →Chemistry · THERMODYNAMICS
Match List-I with List-II: List-I (Chemical Reaction) List-II (Enthalpy vs Internal Energy Relation) A \( \text{C}(s) + \text{O}_2(g) \rightarrow \text{CO}_2(g) \) I \( \Delta H = \Delta U - RT \) B \( \text{N}_2(g) + 3\text{H}_2(g) \rightarrow 2\text{NH}_3(g) \) II \( \Delta H = \Delta U + RT \) C \( \text{PCl}_5(g) \rightarrow \text{PCl}_3(g) + \text{Cl}_2(g) \) III \( \Delta H = \Delta U \) D \( \text{H}_2(g) + \frac{1}{2}\text{O}_2(g) \rightarrow \text{H}_2\text{O}(g) \) IV \( \Delta H = \Delta U - 2RT \) Choose the correct answer from the options given below:
Read answer →Chemistry · THERMODYNAMICS
Why is the absolute value of internal energy (\( U \)) of a system impossible to determine, whereas the change in internal energy (\( \Delta U \)) is readily measurable?
Read answer →Chemistry · THERMODYNAMICS
Consider the combustion of liquid benzene: \( 2\text{C}_6\text{H}_6(l) + 15\text{O}_2(g) \rightarrow 12\text{CO}_2(g) + 6\text{H}_2\text{O}(l) \) at \( 298\text{ K} \). The difference between the enthalpy of reaction and internal energy change, \( (\Delta H - \Delta U) \), per mole of benzene combusted is: (Take \( R = 8.314\text{ J}\cdot\text{K}^{-1}\cdot\text{mol}^{-1} \))
Read answer →Chemistry · THERMODYNAMICS
Calculate the standard enthalpy change for the reaction: \( \text{N}_2(g) + 3\text{H}_2(g) \rightarrow 2\text{NH}_3(g) \) using the bond enthalpy data: \( \text{B.E.}(\text{N}\equiv\text{N}) = 946\text{ kJ mol}^{-1} \), \( \text{B.E.}(\text{H}-\text{H}) = 435.8\text{ kJ mol}^{-1} \), and \( \text{B.E.}(\text{N}-\text{H}) = 389\text{ kJ mol}^{-1} \).
Read answer →Chemistry · THERMODYNAMICS
For the dissociation of crystal lattice: \( \text{NaCl}(s) \rightarrow \text{Na}^+(g) + \text{Cl}^-(g) \), the lattice enthalpy is \( \Delta_{\text{lattice}} H^\ominus = +788\text{ kJ mol}^{-1} \) at \( 298\text{ K} \). Assuming ideal gas behavior for ions, what is the change in internal energy (\( \Delta_{\text{lattice}} U^\ominus \))? (Take \( 2RT \approx 5\text{ kJ mol}^{-1} \))
Read answer →Chemistry · THERMODYNAMICS
For most ionic compounds, the enthalpy of solution (\( \Delta_{\text{sol}} H^\ominus \)) is positive, yet they dissolve in water. Why does the solubility of most such salts increase with a rise in temperature?
Read answer →Chemistry · THERMODYNAMICS
A reaction has \( \Delta H = +60\text{ kJ mol}^{-1} \) and \( \Delta S = +150\text{ J K}^{-1}\text{mol}^{-1} \). What is the minimum temperature above which the reaction becomes spontaneous?
Read answer →Chemistry · THERMODYNAMICS
Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): Combustion reactions of hydrocarbons are invariably exothermic in nature. Reason (R): The standard enthalpy of combustion (\( \Delta_c H^\ominus \)) is defined as the enthalpy change accompanying the complete combustion of one mole of a substance in presence of excess oxygen. In the light of the above statements, choose the correct answer from the options given below:
Read answer →Chemistry · THERMODYNAMICS
Consider the following statements regarding bond enthalpies and atomization enthalpies: (A) For diatomic molecules like \( \text{H}_2(g) \), the bond dissociation enthalpy is identical to the enthalpy of atomization. (B) For polyatomic molecules like \( \text{CH}_4(g) \), all four \( \text{C}-\text{H} \) bond dissociation enthalpies are experimentally identical. (C) Enthalpy of atomization of sodium metal is equal to its enthalpy of sublimation. (D) Reaction enthalpies in the gas phase can be calculated using: \( \Delta_r H^\ominus = \sum \text{bond enthalpies}_{\text{products}} - \sum \text{bond enthalpies}_{\text{reactants}} \). Choose the correct answer from the options given below:
Read answer →Chemistry · THERMODYNAMICS
For a reaction in equilibrium, the relationship between the standard Gibbs energy change \( \Delta_r G^\circ \) and the equilibrium constant \( K \) is given by:
Read answer →Chemistry · THERMODYNAMICS
Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): For chemical reactions involving only condensed phases (solids and liquids), the difference between \( \Delta H \) and \( \Delta U \) is usually very large. Reason (R): Solids and liquids do not suffer any significant volume changes upon heating or during reaction. In the light of the above statements, choose the correct answer from the options given below:
Read answer →Chemistry · THERMODYNAMICS
Using the mean bond enthalpy values: \( \Delta_{\text{C}-\text{C}} H^\ominus = 347\text{ kJ mol}^{-1} \), \( \Delta_{\text{C}=\text{C}} H^\ominus = 611\text{ kJ mol}^{-1} \), \( \Delta_{\text{C}-\text{H}} H^\ominus = 414\text{ kJ mol}^{-1} \), and \( \Delta_{\text{H}-\text{H}} H^\ominus = 435.8\text{ kJ mol}^{-1} \), what is the standard enthalpy of reaction for the hydrogenation of ethene: \( \text{CH}_2=\text{CH}_2(g) + \text{H}_2(g) \rightarrow \text{CH}_3-\text{CH}_3(g) \)?
Read answer →Chemistry · THERMODYNAMICS
Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): A decrease in enthalpy (\( \Delta H < 0 \)) is the sole and sufficient criterion for the spontaneity of a chemical process. Reason (R): Many endothermic reactions (\( \Delta H > 0 \)) proceed spontaneously at room temperature or elevated temperatures. In the light of the above statements, choose the correct answer from the options given below:
Read answer →Chemistry · THERMODYNAMICS
Given below are statements regarding extensive and intensive thermodynamic properties: (A) Volume and internal energy are extensive properties. (B) Density and molar heat capacity are intensive properties. (C) Heat capacity (\( C \)) is an intensive property. (D) The ratio of two extensive properties is always an intensive property. Choose the correct answer from the options given below:
Read answer →Chemistry · THERMODYNAMICS
