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Define standard enthalpy of formation. - Chemistry

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प्रश्न

Define standard enthalpy of formation.

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उत्तर

The standard enthalpy of formation of a compound is the enthalpy change that accompanies a reaction in which one mole of pure compound in its standard state is formed from its elements in their standard states.

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Thermochemistry
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पाठ 4: Chemical Thermodynamics - Short answer questions (Type- II)

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एससीईआरटी महाराष्ट्र Chemistry [English] 12 Standard HSC
पाठ 4 Chemical Thermodynamics
Short answer questions (Type- II) | Q 4

संबंधित प्रश्‍न

Select the most appropriate option.

Which of the following reactions is exothermic?


Answer in brief.

What is the standard enthalpy of combustion? Give an example.


Answer the following question.

State Hess’s law of constant heat summation. Illustrate with an example. State its applications.


The enthalpy change for the reaction, \[\ce{C2H4_{(g)} + H2_{(g)} -> C2H6_{(g)}}\] is −620 J when 100 mL of ethylene and 100 ml of \[\ce{H2}\] react at 1 bar pressure. Calculate the pressure volume type of work and ΔU for the reaction.


Calculate the standard enthalpy of combustion of CH4(g) if ΔfH°(CH4) = – 74.8 kJ mol–1, ΔfH°(CO2) = – 393.5 kJ mol–1 and ΔfH°(H2O) = – 285.8 kJ mol–1.


Calculate the standard enthalpy of formation of liquid methanol from the following data:

  1. \[\ce{CH3OH_{(l)} + \frac{3}{2} O_{2(g)} -> CO_{2(g)} + 2H2O_{(l)}}\]     ∆H° = – 726 kJ mol–1
  2. \[\ce{C_{(Graphite)} + O_{2(g)} -> CO_{2(g)}}\]          ∆cH° = – 393 kJ mol–1
  3. \[\ce{H_{2(g)} + \frac{1}{2} O_{2(g)} -> H2O_{(l)}}\]          ∆fH° = – 286 kJ mol–1 

Define the Enthalpy of ionisation.


Classify the following into intensive and extensive properties.

Pressure, volume, mass, temperature.


When 2 moles of C2H6(g) are completely burnt, 3129 kJ of heat is liberated. If ∆Hf for CO2(g) and H2O(l) are −395 and −286 kJ per mole respectively, the heat combustion of C2H6(g) is ____________.


The volume of oxygen required for complete combustion of 0.25 mole of methane at STP is ______.


The heat of formations of CO(g) and CO2(g) are −26.4 kcal and −94.0 kcal respectively. The heat of combustion of carbon monoxide will be ____________.


The enthalpy of formation of nitrogen dioxide is +33.2 kJ mol−1. The enthalpy of the reaction \[\ce{2N2_{(g)} + 4O2_{(g)} -> 4NO2_{(g)}}\]; is ____________.


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 ________.


Heat of formation of water is - 272 kJ mol-1. What quantity of water is converted to H2 and O2 by 750 kJ of heat?


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)?


Which of the following equations has ΔfH° and ΔH° same?


Calculate the standard enthalpy of:

\[\ce{N2H_{4(g)} + H_{2(g)} -> 2NH_{3(g)}}\]

If ΔH0(N – H) = 389 kJ mol–1, ΔH0(H – H) = 435 kJ mol–1, ΔH0(N – N) = 159 kJ mol–1.


Identify the invalid equation.


What is the amount of water formed by the combustion of 1.6 g methane?


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 ______.


What is enthalpy of formation of NH3 if bond enthalpies as (N ≡ N) = - 941 kJ/mol.

\[\ce{(H - H)}\] = 436 kJ/mol and \[\ce{(N - H)}\] = 389 kJ/mol?


The enthalpy change that accompanies a reaction in which 1 mole of its standard state is formed from its elements in their standard states


Calculate the standard enthalpy of the reaction, \[\ce{SiO2_{(s)} + 3C_{(graphite)} -> SiC_{(s)} + 2CO_{(g)}}\] from the following reactions:

  1. \[\ce{Si_{(s)} + O2_{(g)} -> SiO2_{(s)}}\], ΔrH0 = −911 kJ
  2. \[\ce{2C_{(graphite)} + O2_{(g)} -> 2CO_{(g)}}\], ΔrH= −221 kJ
  3. \[\ce{Si_{(s)} + C_{(graphite)} -> SiC_{(s)}}\], ΔrH= −65.3 kJ

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


Draw energy profile diagram and show:

  1. activated complex
  2. energy of activation for forward and backward reactions
  3. enthalpy of reaction

The heat evolved in the combustion of 6.022 x 1021 carbon particles is 3.94 kJ. The heat of combustion of carbon is ______.


For the reaction, H2 + I2 ⇌ 2HI; ΔH = 12.4 kcal. The heat of formation of HI, ΔHf = ______.


Calculate ΔsubH of the H2O from the given data:
\[\ce{H2O_{(s)}->H2O_{(l)},}\] ΔfusH = 6.01kJ mol−1

\[\ce{H2O_{(l)}-> H2O_{(g)},}\] ΔVapH = 45.07 kJ mol−1.


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