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महाराष्ट्र राज्य शिक्षण मंडळएचएससी विज्ञान (सामान्य) इयत्ता १२ वी

Define the Bond enthalpy.

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प्रश्न

Define the Bond enthalpy.

व्याख्या
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उत्तर

The enthalpy change required to break a particular covalent bond in one mole of the gaseous molecule to produce gaseous atoms and/or radicals is called bond enthalpy.

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पाठ 4: Chemical Thermodynamics - Long answer questions

संबंधित प्रश्‍न

Answer in brief.

How will you calculate reaction enthalpy from data on bond enthalpies?


Answer in brief.

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


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


Calculate the total heat required

a) to melt 180 g of ice at 0 °C

b) heat it to 100 °C and then

c) vapourise it at that temperature.

[Given: ΔfusH° (ice) = 6.01 kJ mol-1 at 0 °C, ΔvapH° (H2O) = 40.7 kJ mol-1 at 100 °C, Specific heat of water is 4.18 J g-1 K-1]


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.


Define the Standard enthalpy of combustion.


The enthalpy change of the following reaction:

\[\ce{CH_{4(g)} + Cl_{2(g)} -> CH3Cl_{(g)} + HCl_{(g)}ΔH^0 = –104 kJ}\]

Calculate C – Cl bond enthalpy. The bond enthalpies are:

Bond C − H Cl − Cl H − Cl
∆H°/kJ mol−1 414 243 431

Define the Enthalpy of ionisation.


Write an application of Hess’s law.


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


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 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?


Calculate the enthalpy of hydrogenation of C2H4(g), given that the enthalpy of formation of ethane and ethylene are −30.2 kcal and +12.5 kcal respectively.


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 ____________.


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


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. \[\ce{H2_{(g)} + 1/2 O2_{(g)} -> H2O_{(l)}Δ_fH^° = - 286 kJ mol^{-1}}\]

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.


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


How many moles of helium gas occupies 22.4 Lat 0°c and at 1 atmospheric pressure?


Define and explain the term, enthalpy of reaction.


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

Which of the following reactions defines the enthalpy of formation?


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


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

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


Heat of combustion of CH4(g) is -890 kJ/mole. What is the value of Δc H of 8gm of methane?


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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