Advertisements
Advertisements
Question
Calculate the standard enthalpy of formation of \[\ce{CH3OH_{(l)}}\] from the following data:
\[\ce{CH3OH_{(l)} + 3/2 O2_{(g)} -> CO2_{(g)} + 2H2O_{(l)} }\]; ΔrH° = − 726 kJ mol-1
\[\ce{C_{(graphite)} + O2_{(g)} -> CO2_{(g)}}\]; ΔcH° = −393 kJ mol−1
\[\ce{H2_{(g)} + 1/2 O_{(g)} -> H2O_{(l)}}\]; ΔfH° = −286 kJ mol−1
Advertisements
Solution
Given: Given equations are,
\[\ce{CH3OH_{(l)} + 3/2 O2_{(g)} -> CO2_{(g)} + 2H2O_{(l)} }\]; ΔrH° = − 726 kJ mol-1 ...(i)
\[\ce{C_{(graphite)} + O2_{(g)} -> CO2_{(g)}}\]; ΔcH° = −393 kJ mol−1 ...(ii)
\[\ce{H2_{(g)} + 1/2 O_{(g)} -> H2O_{(l)}}\]; ΔfH° = −286 kJ mol−1 ...(iii)
To find: The standard enthalpy of formation (ΔfH°) of \[\ce{CH3OH_{(l)}}\]
Calculation:
Required equation is, \[\ce{C_{(graphite)} + 2H2_{(g)} + 1/2 O2_{(g)} -> CH3OH_{(l)}}\]
Multiply equation (iii) by 2 and add to equation (ii),
\[\ce{2H2_{(g)} + O2_{(g)} -> 2H2O_{(l)}}\]; ΔfH° = −572 kJ mol−1
\[\ce{C_{(graphite)} + O2_{(g)} -> CO2_{(g)}}\]; ΔcH° = −393 kJ mol−1
________________________________________________________________________
\[\ce{C_{(graphite)} + 2H2_{(g)} + 2O2_{(g)} -> CO2_{(g)} + 2H2O_{(l)}}\], ΔrH° = −572 −393 = −965kJ mol−1 ...(iv)
Reverse equation (i) and add to equation (iv),
\[\ce{CO2_{(g)} + 2H2O_{(l)} -> CH3OH_{(l)} + 3/2O2_{(g)}}\], ΔrH° = − 726 kJ mol-1
\[\ce{C_{(graphite)} + 2H2_{(g)} + 2O2_{(g)} -> CO2_{(g)} + 2H2O_{(l)}}\], ΔrH° = −965
_____________________________________________________________________________
\[\ce{C_{(graphite)} + 2H2_{(g)} + 1/2O2_{(g)} -> CO2_{(g)} + CH3OH_{(l)}}\], ΔfH° = ΔrH° = 726 −965 = −239kJ mol−1
∴ The standard enthalpy of formation (ΔfH°) of \[\ce{CH3OH_{(l)}}\] from the given data is −239kJ mol−1
APPEARS IN
RELATED QUESTIONS
Select the most appropriate option.
Bond enthalpies of H–H, Cl–Cl, and H–Cl bonds are 434 kJ mol–1, 242 kJ mol–1, and 431 kJ mol–1, respectively. Enthalpy of formation of HCl is _______.
Answer the following question.
When 6.0 g of O2 reacts with CIF as per
\[\ce{2ClF_{(g)} + O2_{(g)} -> Cl2O_{(g)} + OF2_{(g)}}\]
The enthalpy change is 38.55 kJ. What is the standard enthalpy of the reaction? (Δr H° = 205.6 kJ)
Define enthalpy of combustion.
Define enthalpy of neutralization.
Enthalpy of neutralization is always a constant when a strong acid is neutralized by a strong base: account for the statement.
Derive the relation between ∆H and ∆U for an ideal gas. Explain each term involved in the equation.
The standard enthalpy of formation of ammonia is −46.0 kJ mol−1. The enthalpy change for the reaction:
\[\ce{2NH3_{(g)} -> 2N2_{(g)} + 3H2_{(g)}}\] is ____________.
For which of the following ∆U = ∆H?
When 6.0 g of O2 reacts with CIF as per \[\ce{2ClF_{(g)} + O2_{(g)} -> Cl2O_{(g)} + OF2_{(g)}}\] the enthalpy change is 38.55 kJ. The standard enthalpy of the reaction is ____________.
Identify the equation in which change in enthalpy is equal to change in internal energy.
The enthalpy change for two reactions are given by the equations
\[\ce{2Cr_{(s)} + 1.5 O2_{(g)} -> Cr2O3_{(s)}}\];
∆H1 = −1130 kJ ............(i)
\[\ce{C_{(s)} + 0.5 O2_{(g)} -> CO_{(g)}}\];
∆H2 = −110 kJ .........(ii)
What is the enthalpy change, in kJ, for the following reaction?
\[\ce{3C_{(s)} + Cr2O3_{(s)} -> 2Cr_{(s)} + 3CO_{(g)}}\]
Given the bond energies N ≡ N, H – H and N – H bonds are 945, 436 and 391 kJ/mol respectively. The enthalpy of the reaction;
\[\ce{N2_{(g)} + 3H2_{(g)} -> 2NH3_{(g)}}\]
In which of the following reactions does the heat change represent the heat of formation of water?
If 2 kJ of heat is released from system and 6 kJ of work is done on the system, what is enthalpy change of system?
For the reaction, \[\ce{N_{2(g)} + 3H_{2(g)} -> 2NH_{3(g)}}\], ΔH is equal to ______.
In which of the following reactions, ΔH is not equal to ΔU?
The work done during combustion of 9 × 10-2 kg of ethane, C2H6 (g) at 300 K is ______.
(Given R = 8.314 J deg-1, atomic mass C = 12, H = 1)
Calculate ΔU if 2 kJ heat is released and 10 kJ of work is done on the system.
Calculate the work done during the combustion of 0.138 kg of ethanol, C2H5OH(l) at 300 K.
Given: R = 8.314 Jk−1 mol−1, molar mass of ethanol = 46 g mol−1.
Calculate ΔS of the surrounding if the standard enthalpy of formation of methanol is − 238.9 kJ mol−1.
In a particular reaction, 2 kJ of heat is released by the system and 8 kJ of work is done on the system. Determine ΔU.
Define enthalpy.
\[\ce{C(s) + 2H2(g) → CH4(g)}\]; ΔH= –74.8 kJ mol−1. Which of the following diagrams gives an accurate representation of the above reaction?
The equilibrium concentrations of the species in the reaction \[ \mathrm{A} + \mathrm{B} \rightleftharpoons \mathrm{C} + \mathrm{D} \] are 2, 3, 10 and 6 mol L-1, respectively at 300 K. ΔGº for the reaction is (R = 2 cal/mol K)
