Chemical Thermodynamics
Topics
- System, surroundings, extensive/intensive properties, state functions, processes
- First law: work, heat, internal energy, enthalpy
- Heat capacity and molar heat capacity
- Hess's law and enthalpies of reactions (bond dissociation, combustion, formation etc.)
- Second law, entropy and spontaneity
- Gibbs energy change and equilibrium constant
Chapter tests
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See all →- C(s) + 2H_2(g) → CH_4(g); Δ H = -74.8 kJ mol^-1Which of the following diagrams gives an accurate representation of the above reaction? [R → reactants; P → products] Answer: 1. Energy diagram (1) Key idea: Δ H=-74.8 kJ/mol means an exothermic reaction: products lie 74.8 kJ below the reactants. Diagram (1)... 1
- The standard heat of formation, in kcal/mol of Ba^2+ is :[Given : standard heat of formation of SO_4^2- ion (aq) = -216 kcal/mol, standard heat of crystallisation of BaSO_4(s) = -4.5 kcal/mol, standard heat of formation of BaSO_4(s) = -349 kcal/mol] Answer: 1. -128.5 Key idea: mathrmBa²⁺(aq)+SO₄²⁻(aq)→ BaSO₄(s) has Δ H=-4.5 kcal (crystallisation). Δ H_f(BaSO₄)=Δ H_f(mathrmBa²⁺)+Δ H_f(mat... 1
- The work done during reversible isothermal expansion of one mole of hydrogen gas at 25^°C from pressure of 20 atmosphere to 10 atmosphere is:(Given R = 2.0 cal K^-1 mol^-1) Answer: 3. - 413.14 calories Key idea: for reversible isothermal expansion, w=-2.303 nRTlogP₁/P₂ (work done by the gas is negative in this c... 1
- In which of the following processes entropy increases?A. A liquid evaporates to vapour.B. Temperature of a crystalline solid lowered from 130 K to 0 K.C. 2NaHCO_3(s) → Na_2CO_3(s) + CO_2(g) + H_2O_(g)D. Cl_2(g) → 2Cl_(g)Choose the correct answer from… Answer: 4. A, C and D Key idea: entropy rises with disorder, i.e. when more gas or more particles are formed. A: liquid to vapour, disorder... 1
- Match List I with List II.List I (Process): A. Isothermal process B. Isochoric process C. Isobaric process D. Adiabatic processList II (Conditions): I. No heat exchange II. Carried out at constant temperature III. Carried out at constant volume IV. C… Answer: 1. A-II, B-III, C-IV, D-I Key idea: the prefix tells the fixed quantity. Isothermal: constant temperature (II). Isochoric: constant... 1
- The equilibrium concentrations of the species in the reaction A + B ⇌ C + D are 2, 3, 10 and 6 mol L^-1, respectively at 300 K. Δ G^° for the reaction is (R = 2 cal / mol K) Answer: 4. -1381.80 cal Key idea: Δ G^° = -2.303 RTlog K . K = [C][D]/[A][B] = 10 × 6/2 × 3 = 10 , so log K = 1 . Δ G^° = -2.303 × 2 × 300 ×... 1