Advertisements
Advertisements
Questions
Obtain the relationship between ΔH and ΔU for gas phase reactions.
Derive the relation between ΔH and ΔU for a gaseous phase reaction.
Advertisements
Solution
At constant pressure, ΔH and ΔU are related as,
ΔH = ΔU + PΔV ...(1)
For reactions involving gases, ΔV cannot be neglected.
Therefore, ΔH = ΔU + PΔV
= ΔU + P(V2 – V1)
= ΔU + PV2 – PV1 ...(2)
Where V1 is the volume of gas-phase reactants, and V2 is that of the gaseous products.
We assume the reactant and product behave ideally. Applying the ideal gas equation, PV = nRT. Suppose that n1 moles of gaseous reactants produce n2 moles of gaseous products. Then,
PV1 = n1RT and PV2 = n2RT ...(3)
Substitution of equation (3) into equation (2) yields:
ΔH = ΔU + n2RT – n1RT
= ΔU + (n2 – n1) RT
= ΔU + Δng RT ...(4)
Where, Δng is the difference between the number of moles of products and those of reactants.
APPEARS IN
RELATED QUESTIONS
Select the most appropriate option.
If the standard enthalpy of formation of methanol is –238.9 kJ mol–1 then entropy change of the surroundings will be _______.
Answer the following question.
Calculate standard enthalpy of reaction,
Fe2O3(s) + 3CO(g) → 2Fe(s) + 3CO2(g), from the following data.
Δf H°(Fe2O3) = - 824 kJ/mol,
Δf H°(CO) = - 110 kJ/mol,
Δf H°(CO2) = - 393 kJ/mol
Calculate the amount of work done in the
1) Oxidation of 1 mole HCl(g) at 200 °C according to reaction.
4HCl(g) + O2(g) → 2Cl2(g) + 2H2O(g)
2) Decomposition of one mole of NO at 300 °C for the reaction
2NO(g) → N2(g) + O2(g)
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)
Calculate the work done and comment on whether work is done on or by the system for the decomposition of 2 moles of NH4NO3 at 100 °C
NH4NO3(s) → N2O(g) + 2H2O(g)
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.
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 ____________.
When 4 g of iron is burnt to ferric oxide at constant pressure, 29.28 kJ of heat is evolved. What is the enthalpy of formation of ferric oxide?
(Atomic mass of Fe = 56)
In which of the following reactions does the heat change represent the heat of formation of water?
In which of the following reactions, ∆H is greater than ∆U?
For the reaction, \[\ce{A_{(s)} + 2B_{(g)} -> 5C_{(s)} + D_{(l)}}\], ∆H and ∆U are related as ____________.
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?
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 the work done in oxidation of so2(g) at 25°C if, \[\ce{2SO_{2(g)} + O2_{(g)} -> 2SO_{3(g)}}\], R = 8.314 J K−1 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.
Calculate work done in oxidation of 4 moles of SO2 at 25°C. (Given: R = 8.314 JK−1 mol−1 ).
Define enthalpy.
Calculate the standard entropy change of the surrounding if standard enthalpy of formation of methyl alcohol is –240 kJ mol-1.
