General
✓✗For the vaporisation of water at 1 atmosphere pressure, the values of ΔH and ΔS are 40.63 kJ mol−1 and 108.8 J K−1 mol−1 respectively. The temperature at which the Gibbs energy change (ΔG) for this transformation will be zero is
- 393.4 K
- 373.4 K
- 293.4 K
- 273.4 K
General
✓✗For the reaction H2O(l) → H2O(g) at 373 K and 1 atm,
- ΔSsystem = 0
- ΔStotal = 0
- ΔStotal > 0
- ΔStotal < 0
General
✓✗Given: ΔfH° of NH3(g) = −46 kJ mol−1, bond enthalpy of N≡N = 946 and of H−H = 436 kJ mol−1. The average N−H bond enthalpy in ammonia is about
- 360 kJ mol−1
- 437 kJ mol−1
- 1173 kJ mol−1
- 391 kJ mol−1
General
✓✗A gas in a cylinder fitted with a piston absorbs 1.0 kJ of heat and expands from 2.0 L to 7.0 L against a constant pressure of 1.0 bar. Then it is compressed back to 2.0 L by a constant pressure of 2.0 bar with no heat exchange. The net change in internal energy for the two steps is (1 L bar = 100 J)
- +1.5 kJ
- 0
- +1.0 kJ
- +0.5 kJ
General
✓✗If a chemical equation is reversed, the value of ΔH
- is doubled
- changes sign but keeps the same magnitude
- becomes zero
- remains the same
General
✓✗The first ionisation enthalpy of Na is 496 kJ mol−1. The energy required to convert 2.3 g of gaseous Na atoms into gaseous Na+ ions is
- 1140 kJ
- 496 kJ
- 49.6 kJ
- 4.96 kJ
General
✓✗The heat capacity of a substance at constant pressure (Cp) is defined as
- \( \left(\dfrac{\partial H}{\partial T}\right)_p \)
- \( \left(\dfrac{\partial H}{\partial p}\right)_T \)
- \( \left(\dfrac{\partial U}{\partial T}\right)_p \)
- \( \left(\dfrac{\partial S}{\partial T}\right)_V \)
General
✓✗The reaction C2H4(g) + H2(g) → C2H6(g) is exothermic because
- breaking bonds releases energy
- the number of gas moles increases
- the energy released in forming one C−C and two C−H bonds exceeds that needed to break one C=C and one H−H bond
- C=C is weaker than C−C
General
✓✗Enthalpy changes of reactions carried out in an open coffee-cup calorimeter are measured at constant
- pressure
- internal energy
- entropy
- volume
General
✓✗In which of the following does the entropy decrease?
- 2SO2(g) + O2(g) → 2SO3(g)
- CaCO3(s) → CaO(s) + CO2(g)
- N2O4(g) → 2NO2(g)
- I2(s) → I2(g)
General
✓✗A gas is compressed from 10 L to 4 L by a constant external pressure of 2 atm. The work done on the gas is
- −12 L atm
- +28 L atm
- −28 L atm
- +12 L atm
General
✓✗Given (kJ mol−1): ΔsubH(K) = 89, IE(K) = 419, ½D(Cl2) = 122, ΔegH(Cl) = −349, lattice enthalpy of KCl (dissociation) = +717. The enthalpy of formation of KCl(s) is
- +436 kJ mol−1
- −998 kJ mol−1
- −281 kJ mol−1
- −436 kJ mol−1
General
✓✗In a cyclic process, a system absorbs 100 J of heat. The work done on the system is
- +200 J
- +100 J
- −100 J
- 0
General
✓✗Which of the following statements is correct for an ideal gas?
- In an adiabatic process, ΔU = 0.
- In an isothermal process, ΔU = 0 and ΔH = 0.
- In an isochoric process, w = q.
- In a cyclic process, q = 0.
General
✓✗For a sample of a perfect gas, when its pressure is changed isothermally from pi to pf, the entropy change is given by
- \( \Delta S = nR\ln\dfrac{p_f}{p_i} \)
- \( \Delta S = nR\ln\dfrac{p_i}{p_f} \)
- \( \Delta S = nRT\ln\dfrac{p_f}{p_i} \)
- \( \Delta S = RT\ln\dfrac{p_i}{p_f} \)