हिंदी

Write an application of Hess’s law.

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प्रश्न

Write an application of Hess’s law.

एक पंक्ति में उत्तर
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उत्तर १

The Hess's law has been useful to calculate the enthalpy changes for the reactions with their enthalpies being not known experimentally.

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उत्तर २

  1. It helps in calculating the enthalpies of formation of those compounds which cannot be determined experimentally.
  2. It helps in determining the enthalpy of allotropic transformation like C(graphite)→C(diamond)
  3. It helps in calculating the enthalpy of hydration.
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अध्याय 4: Chemical Thermodynamics - Long answer questions

संबंधित प्रश्न

Select the most appropriate option.

Which of the following reactions is exothermic?


Answer the following in one or two sentences.

What is standard state of a substance?


Answer the following question.

Calculate ΔrH° for the following reaction at 298 K:

1) 2H3BO3(aq) → B2O3(s) + 3H2O(l), ΔrH° = + 14.4 kJ

2) H3BO3(aq) → HBO2(aq) + H2O(l), ΔrH° = - 0.02 kJ

3) H2B4O7(s) → 2B2O3(s) + H2O(l), ΔrH° = + 17.3 kJ


The standard enthalpy of formation of water is - 286 kJ mol-1. Calculate the enthalpy change for the formation of 0.018 kg of water.


Calculate enthalpy of formation of HCl if bond enthalpies of H2, Cl2 and HCl are 434 kJ mol-1, 242 kJ mol–1 and 431 kJ mol–1 respectively.


Define the Standard enthalpy of combustion.


Define the Bond enthalpy.


Define the Enthalpy of ionisation.


A compound that has a high negative heat of formation is normally ____________.


The standard heats of formation for CCl4(g), H2O(g), CO2(g), and HCl(g) are −25.5, −57.8, −94.1 and −22.1 kcal mol−1, respectively.

∆H for the reaction

\[\ce{CCl4_{(g)} + 2H2O_{(g)} -> CO2_{(g)} + 4HCl_{(g)}}\] at 298 K


The standard heats of formation in kcal mol−1 of NO2(g) and N2O4(g) are 8.0 and 2.0 respectively. The heat of dimerization of NO2 in kcal is ____________.

\[\ce{2NO2_{(g)} ⇌ N2O4_{(g)}}\]


\[\ce{S + 3/2O2 -> SO3 +2{x} kcal}\] .........(i)

\[\ce{SO2 + 1/2O2 -> SO3 + {y} kcal}\] .......(ii)

The heat of formation of SO2 is ____________.


The heat evolved in the combustion of benzene is given by

\[\ce{C6H6 + 7 1/2O2 -> 6CO2_{(g)} + 3H2O_{(l)}}\]; ΔH = −3264.6 kJ

Which of the following quantities of heat energy will be evolved when 39 g C6H6 are burnt?


Which of the following compounds is Not present in its standard state at 25°C and 1 atmosphere pressure?


Enthalpy of formation of two compounds x and y are −84 kJ and −156 kJ respectively. Which of the following statements is CORRECT?


Given that,

\[\ce{C_{(s)} + O_{2(g)} -> CO_{2(g)}}\]   ΔH° = -X kJ

\[\ce{2CO_{(g)} + O_{2(g)} -> 2CO_{2(g)}}\]   ΔH° = - Y kJ, then standard enthalpy of formation of carbon monoxide is ________.


An ideal gas expands isothermally and reversibly from 10 m3 to 20 m3 at 300 K performing 5 .187 kJ of work on surrounding. Calculate number of moles of gas undergoing expansion. (R = 8.314 J K-1 mol-1)


Standard entropies of N2(g), H2(g), and NH3(g) are a1, a2 and a3 J K-1 mol-1 respectively. What is value of ΔS° for formation of NH3(g)?


Calculate the standard enthalpy of formation of CH3OH(l) from the following data:

  1. \[\ce{CH3OH_{(l)} + 3/2 O2_{(g)} -> CO2_{(g)} + 2H2O_{(l)}ΔH^° = - 726 kJ mol^{-1}}\]
  2. \[\ce{C_{(s)} + O2_{(g)} → CO2_{(g)}Δ_cH^° = – 393 kJ mol^{-1}}\]
  3. \[\ce{H2_{(g)} + 1/2 O2_{(g)} -> H2O_{(l)}Δ_fH^° = - 286 kJ mol^{-1}}\]

\[\ce{A -> B}\], ∆H = −10 kJ mol−1, Ea(f) = 50 kJ mol−1, then Ea of \[\ce{B -> A}\] will be ______.


When the enthalpy of combustion of carbon to carbon dioxide is - 360 kJ mol-1, then the enthalpy change for the formation of 18 g of CO2 from carbon and dioxygen at the same temperature in kJ will be ______.


Which of the following reactions defines the enthalpy of formation?


Standard enthalpy of combustion of a substance is given. Then Write thermochemical equation.

ΔcH0[C2H5OH(1)] = - 1409 kJ mol-1


Standard enthalpy of combustion of a substance is given. Then Write thermochemical equation.

ΔcH0[CH3CHO(l)] = - 1166 kJ mol-1


Calculate heat evolved for combustion of 13 gm of acetylene (C2H2).

Given: \[\ce{C2H2_{(g)} + 5/2O_{2(g)}-> 2CO_{2(g)} + H2O_{(l)} \Delta_{(c)}H^{0} = - 1300 kJ}\]


Calculate the standard enthalpy of combustion of methane if the standard enthalpy of formation of methane, carbon dioxide and water are −74.8, −393.5 and −285.8 kJmol−1 respectively.


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