Chapter 6 - Thermodynamics
Pages 182 - 184
Choose the correct answer. A thermodynamic state function is a quantity
(i) used to determine heat changes
(ii) whose value is independent of path
(iii) used to determine pressure-volume work
(iv) whose value depends on temperature only.
For the process to occur under adiabatic conditions, the correct condition is:
(i) ΔT = 0
(ii) Δp = 0
(iii) q = 0
(iv) w = 0
The enthalpies of all elements in their standard states are:
(iii) < 0
(iv) different for each element
ΔUθof combustion of methane is – X kJ mol–1. The value of ΔHθ is
(i) = ΔUθ
(ii) > ΔUθ
(iii) < ΔUθ
(iv) = 0
The enthalpy of combustion of methane, graphite and dihydrogen at 298 K are, –890.3 kJ mol–1 –393.5 kJ mol–1, and –285.8 kJ mol–1 respectively. Enthalpy of formation of CH4(g) will be
(i) –74.8 kJ mol–1
(ii) –52.27 kJ mol–1
(iii) +74.8 kJ mol–1
(iv) +52.26 kJ mol–1.
A reaction, A + B → C + D + q is found to have a positive entropy change. The reaction will be
(i) possible at high temperature
(ii) possible only at low temperature
(iii) not possible at any temperature
(iv) possible at any temperature
In a process, 701 J of heat is absorbed by a system and 394 J of work is done by the system. What is the change in internal energy for the process?
The reaction of cyanamide, NH2CN(s),with dioxygen was carried out in a bomb calorimeter, and ΔUwas found to be –742.7 kJ mol–1at 298 K. Calculate enthalpy change for the reaction at 298 K.
`NH_2 CN(g) + 3/2 O_2(g) -> N_2(g) + CO_2(g) + H_2O(1)`
Calculate the number of kJ of heat necessary to raise the temperature of 60.0 g of aluminium from 35°C to 55°C. Molar heat capacity of Al is 24 J mol–1 K–1.
Calculate the enthalpy change on freezing of 1.0 mol of water at 10.0°C to ice at –10.0°C. ΔfusH = 6.03 kJ mol–1 at 0°C.
Cp[H2O(l)] = 75.3 J mol–1 K–1
Cp[H2O(s)] = 36.8 J mol–1 K–1
Enthalpy of combustion of carbon to CO2 is –393.5 kJ mol–1. Calculate the heat released upon formation of 35.2 g of CO2 from carbon and dioxygen gas.
Enthalpies of formation of CO(g), CO2(g), N2O(g) and N2O4(g) are –110 kJ mol–1, – 393 kJ mol–1, 81 kJ mol–1 and 9.7 kJ mol–1 respectively. Find the value of ΔrH for the reaction:
N2O4(g) + 3CO(g) → N2O(g) + 3CO2(g)
`N_(2(g)) + 3H_(2(g)) -> 2NH_(3(g))`; ΔrHθ = –92.4 kJ mol–1
What is the standard enthalpy of formation of NH3 gas?
Calculate the standard enthalpy of formation of CH3OH(l) from the following data:
CH3OH(l) + `3/2` O2(g) →CO2(g) + 2H2O(l) ; ΔrHθ = –726 kJ mol–1
C(g) + O2(g) →CO2(g) ; ΔcHθ = –393 kJ mol–1
H2(g) +`1/2` O2(g) → H2O(l) ; ΔfHθ = –286 kJ mol–1.
Calculate the enthalpy change for the process
CCl4(g) → C(g) + 4Cl(g)
and calculate bond enthalpy of C–Cl in CCl4(g).
ΔvapHθ (CCl4) = 30.5 kJ mol–1.
ΔfHθ (CCl4) = –135.5 kJ mol–1.
ΔaHθ (C) = 715.0 kJ mol–1, where ΔaHθ is enthalpy of atomisation
ΔaHθ (Cl2) = 242 kJ mol–1
For an isolated system, ΔU = 0, what will be ΔS?
For the reaction at 298 K,
2A + B → C
ΔH = 400 kJ mol–1 and ΔS = 0.2 kJ K–1 mol–1
At what temperature will the reaction become spontaneous considering ΔH and ΔS to be constant over the temperature range?
For the reaction,2Cl(g) → Cl2(g), what are the signs of ΔH and ΔS?
For the reaction
2A(g) + B(g) → 2D(g)
ΔUθ = –10.5 kJ and ΔSθ= –44.1 JK–1.
Calculate ΔGθ for the reaction, and predict whether the reaction may occur spontaneously.
The equilibrium constant for a reaction is 10. What will be the value of ΔGθ? R = 8.314 JK–1 mol–1,T = 300 K.
Comment on the thermodynamic stability of NO(g), given
`1/2` N2(g) + `1/2` O2(g) → NO(g) ; ΔrHθ = 90 kJ mol–1
NO(g) +`1/2` O2(g) → NO2(g) : ΔrHθ= –74 kJ mol–1
Calculate the entropy change in surroundings when 1.00 mol of H2O(l) is formed under standard conditions. ΔfHθ = –286 kJ mol–1.